Philosophical Geek » Code

A WPF Numeric Entry Control with Pop-up Calculator

Ben — Mon, 31 Jan 2011 18:00:00 +0000

Part 2 – This article

When WPF first shipped, there was a noticeable lack of certain controls we’ve become used to in Win32 and WinForms: Calendar, DateTimePicker, and NumericUpDown. WPF 4 adds Calendar and DatePicker, but not anything for numeric entry.

I described how to create a numeric entry control in a previous article. In this article, I will follow that up by adding a popup calculator to allow you to quickly manipulate the number.

If you find this article useful, you will love my book, C# 4.0 How-To, which is filled with tips such as this.

Adding a Popup Calculator

Now that we have a basic numeric entry control, let’s extend it by adding the power of a keyboard-driven calculator popup window.

If you’ve used Quicken or the now-sadly-defunct Microsoft Money, you’ve seen a feature that pops up a calculator window whenever you hit +, –, *, or / in a number field.

Here are some further requirements for such a control:

It should be activated when the user types +, –, *, or /
It should be dismissed if the user hits Escape, Enter, or clicks anywhere outside the calculator (which is considered equivalent to Enter, not escape)
Both mouse and keyboard input should be handled
This version only handles integers
It should handle Backspace key to erase previously-input character
It should be visually compact
It should allow the user to string computations together. A + B – C / D * E

Extend the Numeric Entry Control

We first need to come up with a way to trigger the calculator in our numeric entry control. This is going to simply be if the user hits any math-operation character, such as +, –, *, or /.

First, we’ll need to define the allowed operations and a way to associate keyboard keys with math operations:

public enum MathOperation

    None = 0,

    Add,

    Subtract,

    Multiply,

    Divide

};

Now, let’s subclass NumericEntryControl with a new class that adds some additional keyboard handling.

class NumericEntryWithCalcControl : NumericEntryControl

    static Dictionary _keyToOp =

        new Dictionary();

    static NumericEntryWithCalcControl()

        //associate keyboard keys with a math operation

        _keyToOp[Key.Add] = MathOperation.Add;

        _keyToOp[Key.Subtract] = MathOperation.Subtract;

        _keyToOp[Key.Multiply] = MathOperation.Multiply;

        _keyToOp[Key.Divide] = MathOperation.Divide;

#if DEBUG

        //easier keys on a laptop

        _keyToOp[Key.A] = MathOperation.Add;

        _keyToOp[Key.S] = MathOperation.Subtract;

        _keyToOp[Key.M] = MathOperation.Multiply;

        _keyToOp[Key.D] = MathOperation.Divide;

#endif

With this bookkeeping down, we can intercept the keystrokes and show our calculator window (which we’ll define later) in the right spot. We also should handle when the window closes.

private CalcWindow _calc = null;

protected override void OnKeyDown(KeyEventArgs e)

    MathOperation op = MathOperation.None;

    if (_keyToOp.TryGetValue(e.Key, out op))

        e.Handled = true;

        HandleOperation(op);

    else

        e.Handled = false;

        base.OnKeyDown(e);

private void HandleOperation(MathOperation mathOperation)

    //show the calc dialog and initialize with Value and Op

    if (mathOperation != MathOperation.None)

        _calc = new CalcWindow(Value, mathOperation);

        _calc.Closed += new EventHandler(calc_Closed);

        Point point = this.PointToScreen(new Point(0, 0));

        //adjust location to correct for DPI settings

        PresentationSource source = PresentationSource.FromVisual(this);

        double dpiX = 96.0 * source.CompositionTarget.TransformToDevice.M11;

        double dpiY = 96.0 * source.CompositionTarget.TransformToDevice.M22;

        _calc.Left = point.X * 96.0 / dpiX;

        _calc.Top = point.Y * 96.0 / dpiY;

        _calc.Show();

private void calc_Closed(object sender, EventArgs e)

    if (_calc != null)

        this.Value = _calc.CurrentValue;

        _calc.Closed -= new EventHandler(calc_Closed);

        _calc = null;

Notice in ProcessOperation that the location of the calculator window is set to the upper left corner of the NumericEntryControl and it takes into account the current DPI. This is important if you’re using anything other than the standard 96 DPI.

Create the Calculator

The actual calculator is a WPF window with no border (or a thin one), a textbox, and buttons representing a standard calculator layout.

The screenshot to the right shows the design layout of this window. The C button clears the input and sets the current value to 0. The left arrow erases the last character you input.

Since this window is designed to popup over other controls, I wanted to keep it as compact as possible.

The XAML code looks like this:

"NumericEntryDemo.CalcWindow"

        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

        xmlns:my="clr-namespace:NumericEntryDemo"

        Title="CalcWindow" WindowStyle="None"

        SizeToContent="WidthAndHeight"

        WindowStartupLocation="Manual"

        ResizeMode="NoResize"

        BorderThickness="1"

        "_textbox"

                 DockPanel.Dock="Top"

                 Margin="2"

                 IsReadOnly="True"

                 Text="{Binding RelativeSource={RelativeSource FindAncestor,

                    AncestorType=my:CalcWindow, AncestorLevel=1}, Path=CurrentValue}"

                 TextAlignment="Right" />

        "4" Rows="5" Width="100" Height="100" Margin="2">

        "0.5,1" StartPoint="0.5,0">

            "White" Offset="0" />

            "#FFDBDBDB" Offset="1" />

All of the click handlers and binding targets will be filled out in the code-behind.

To start with, we need a few housekeeping variables:

The original value upon starting the calculator, just in case after all the calculations the user just hits Escape
A way to track whether we’ve canceled the whole thing
The current operation
The current input, in both string and number form
The previously calculated value, allowing you to string together calculations like “123 + 456 / 2 * 29”
Map buttons and keystrokes to numbers, math operations, and the other commands.

With that, we can see the beginning of our class:

public partial class CalcWindow : Window

    private int _initialValue = 0;

    private bool _canceled = false;

    private MathOperation _currentOp = MathOperation.None;

    //value of current input

    public static readonly DependencyProperty CurrentValueProperty =

        DependencyProperty.Register("CurrentValue", typeof(int),

        typeof(CalcWindow), new PropertyMetadata(0));

    //current input in string form

    public static readonly DependencyProperty CurrentInputProperty =

        DependencyProperty.Register("CurrentInput", typeof(string),

        typeof(CalcWindow), new PropertyMetadata(""));

    //previously calculated value

    public static readonly DependencyProperty PreviousValueProperty =

        DependencyProperty.Register("PreviousValue", typeof(int),

        typeof(CalcWindow), new PropertyMetadata(0));

    private static readonly Dictionaryint> _keyDigits =

        new Dictionaryint>();

    private static readonly Dictionary _keyOps =

        new Dictionary();

    private readonly Dictionaryint> _buttonDigits =

        new Dictionaryint>();

    private readonly Dictionary _buttonOps =

        new Dictionary();

    static CalcWindow()

        _keyDigits[Key.D0] = 0;

        _keyDigits[Key.D1] = 1;

        _keyDigits[Key.D2] = 2;

        _keyDigits[Key.D3] = 3;

        _keyDigits[Key.D4] = 4;

        _keyDigits[Key.D5] = 5;

        _keyDigits[Key.D6] = 6;

        _keyDigits[Key.D7] = 7;

        _keyDigits[Key.D8] = 8;

        _keyDigits[Key.D9] = 9;

        _keyDigits[Key.NumPad0] = 0;

        _keyDigits[Key.NumPad1] = 1;

        _keyDigits[Key.NumPad2] = 2;

        _keyDigits[Key.NumPad3] = 3;

        _keyDigits[Key.NumPad4] = 4;

        _keyDigits[Key.NumPad5] = 5;

        _keyDigits[Key.NumPad6] = 6;

        _keyDigits[Key.NumPad7] = 7;

        _keyDigits[Key.NumPad8] = 8;

        _keyDigits[Key.NumPad9] = 9;

        _keyOps[Key.Add] = MathOperation.Add;

        _keyOps[Key.Subtract] = MathOperation.Subtract;

        _keyOps[Key.Multiply] = MathOperation.Multiply;

        _keyOps[Key.Divide] = MathOperation.Divide;

#if DEBUG

        _keyOps[Key.A] = MathOperation.Add;

        _keyOps[Key.S] = MathOperation.Subtract;

        _keyOps[Key.M] = MathOperation.Multiply;

        _keyOps[Key.D] = MathOperation.Divide;

#endif

    public int CurrentValue

get

            return (Int32)GetValue(CurrentValueProperty);

set

            SetValue(CurrentValueProperty, value);

    public string CurrentInput

get

            return GetValue(CurrentInputProperty) as string;

set

            SetValue(CurrentInputProperty, value);

    public int PreviousValue

get

            return (Int32)GetValue(PreviousValueProperty);

set

            SetValue(PreviousValueProperty, value);

    public CalcWindow(int initialValue, MathOperation operation)

        _initialValue = initialValue;

        _currentOp = operation;

        CurrentValue = _initialValue;

        PreviousValue = CurrentValue;

        InitializeComponent();

        InitializeButtons();

    private void InitializeButtons()

        _buttonDigits[_button0] = 0;

        _buttonDigits[_button1] = 1;

        _buttonDigits[_button2] = 2;

        _buttonDigits[_button3] = 3;

        _buttonDigits[_button4] = 4;

        _buttonDigits[_button5] = 5;

        _buttonDigits[_button6] = 6;

        _buttonDigits[_button7] = 7;

        _buttonDigits[_button8] = 8;

        _buttonDigits[_button9] = 9;

        _buttonOps[_buttonAdd] = MathOperation.Add;

        _buttonOps[_buttonSubtract] = MathOperation.Subtract;

        _buttonOps[_buttonMultiply] = MathOperation.Multiply;

        _buttonOps[_buttonDivide] = MathOperation.Divide;

All that’s left is to the actual work of handling input. Since input can be from both keyboard and button clicks, let’s first define methods to handle the general operations, and we can hook up the input later.

Generic Input Handling

First, we’ll look at the generic input handlers. These are called by the mouse and keyboard handlers and they return true so they can notify the caller of whether they actually handled the operation.

The “C” button on the calculator will not only clear the current input, but set the current value to 0 (I’m not going to bother implementing a “CE” button that clears just the current input, but it would be easy to add).

private bool HandleClear()

   CurrentInput = "";

   CurrentValue = 0;

   return true;

When the user hits escape, you want to close the window, after setting the value back to the initial one.

private bool HandleEscape()

    _canceled = true;

    CurrentValue = _initialValue;

    Close();

    return true;

We need the _canceled flag because, as we’ll see below, when the window is deactivated, under normal circumstances we want to complete the current operation, but in the canceled case we want to do nothing.

When a user hits Enter or presses the Equals button, the current operation should be completed and the window closed. In this control, since we also want the current operation to be completed when the window is deactivated, hitting Equals will just cause the window to close and we’ll handle the calculation in the deactivation code.

private bool HandleEquals()

    //The final operation will be

    //handled when the window closes

    Close();

    return true;

This calculator provides a back button to erase the previously-entered digit. If the input becomes empty, then the current value is set to 0.

private bool HandleBack()

    if (!string.IsNullOrEmpty(CurrentInput))

        CurrentInput = CurrentInput.Substring(0, CurrentInput.Length - 1);

        //this is guaranteed to succeed because we validate when we add digits

        if (!string.IsNullOrEmpty(CurrentInput))

            CurrentValue = Int32.Parse(CurrentInput);

        else

            CurrentValue = 0;

    return true;

When accepting new input, our button and keyboard handlers will ensure that the user can only enter digits, but we also need to make sure we handle integer overflow. An easy way to do this is to treat the new digit as a character and append it to the current input and then reparse it.

private bool HandleDigit(int digit)

    string newInput = CurrentInput + digit.ToString();

    int temp = 0;

    //make sure the full input is a number

    if (Int32.TryParse(newInput, out temp))

        CurrentInput = newInput;

        CurrentValue = temp;

        return true;

    return false;

Finally, when the user selects an operation we need to do one of two things. If there is no current input, then we can just change the current operation to the new one. This lets you change your mind, say if you hit ‘+’, but really wanted ‘-’.

On the other hand, if the user has already entered a number, then you know you’re finishing up the current expression and the user wants to calculate the results and start a new expression. As an example, consider the expression A + B. A is the initial value of the NumericEntryControl, the + is what triggered the calculator to show up, and B is the number the user entered after the calculator was visible. When the next operation is input, A + B should be resolved, placed into A, the current operation set, and the user can now enter the next B, and so on.

private bool HandleOperation(MathOperation op)

    if (CurrentInput.Length > 0)

        ProcessCurrentOperation();

    _currentOp = op;

    return true;

With that, we’ve seen all of the generic input handling. Now let’s move on to the actual math.

Doing the Math

The ProcessCurrentOperation method is the heart of this control as it updates all the values according to the user’s input. Here too we need to consider what happens if the user’s calculations cause an integer overflow. To detect this we need to use a combination of the checked keyword and some exception handling. To simplify things, if this happens, the whole calculation is canceled and the window closed. We also handle divide by zero errors by just setting the new value to 0.

(The checked keyword tells .NET to issue exceptions when integer math overflows. The default behavior depends on compilation and environment settings, but the unchecked behavior is usually what happens).

private void ProcessCurrentOperation()

    if (string.IsNullOrEmpty(CurrentInput))

        return;

    int newValue = 0;

    checked

try

            switch (_currentOp)

                case MathOperation.Add:

                    newValue = PreviousValue + CurrentValue;

                    break;

                case MathOperation.Subtract:

                    newValue = PreviousValue - CurrentValue;

                    break;

                case MathOperation.Multiply:

                    newValue = PreviousValue * CurrentValue;

                    break;

                case MathOperation.Divide:

                    if (CurrentValue != 0)

                        newValue = PreviousValue / CurrentValue;

                    else

                        newValue = CurrentValue;

                    break;

                default:

                    Debug.Assert(false, "Invalid operation. Should never happen!");

                    break;

            CurrentInput = "";

            CurrentValue = newValue;

            PreviousValue = newValue;

        catch (OverflowException)

            //will cause the window to close, so we better cancel everything first

            _canceled = true;

            CurrentValue = _initialValue;

            MessageBox.Show("The result overflowed, calculation canceled.");

Deactivation

As we said before, deaction should cause the current operation to complete, unless the user has canceled.

protected override void OnDeactivated(EventArgs e)

    if (!_canceled)

        ProcessCurrentOperation();

        if (IsVisible)

            //window is still visible if we've

            //clicked away from the window

            //before finishing calculation

            Close();

    base.OnDeactivated(e);

The only thing that remains is hooking up mouse and keyboard input to our existing methods.

Mouse Handling

These are already referenced in the XAML, and all they do is forward to the generic handlers.

void opButton_Click(object sender, RoutedEventArgs e)

    MathOperation op = _buttonOps[sender as Button];

    e.Handled = HandleOperation(op);

void digitButton_Click(object sender, RoutedEventArgs e)

    int digit = _buttonDigits[sender as Button];

    e.Handled = HandleDigit(digit);

private void clearButton_click(object sender, RoutedEventArgs e)

    e.Handled = HandleClear();

private void backButton_Click(object sender, RoutedEventArgs e)

    e.Handled = HandleBack();

private void equalsButton_Click(object sender, RoutedEventArgs e)

    e.Handled = HandleEquals();

Keyboard Handling

To handle the keyboard, we need to preempt the normal message flow by looking at the preview messages (which flow from the top of the UI hierarchy down, rather than the normal messages which bubble from the bottom to the top). If we don’t do this, then when we hit keys like Enter, they go to the button with the current focus, when instead we want it to always cause the Equals functionality.

protected override void OnPreviewKeyDown(KeyEventArgs e)

    /*take over all keyboard input

     * this is important because if a button has focus

     * and we hit enter then the button will be clicked

     * */

    int digit = 0;

    MathOperation op = MathOperation.None;

    if (_keyDigits.TryGetValue(e.Key, out digit))

        e.Handled = HandleDigit(digit);

    else if (_keyOps.TryGetValue(e.Key, out op))

        e.Handled = HandleOperation(op);

    else

        switch (e.Key)

            case Key.Enter:

                e.Handled = HandleEquals();

                break;

            case Key.Escape:

                e.Handled = HandleEscape();

                break;

            case Key.Back:

                e.Handled = HandleBack();

                break;

            case Key.C:

                e.Handled = HandleClear();

                break;

            default:

                e.Handled = false;

                break;

    base.OnPreviewKeyDown(e);

There you have it, a working pop-up calculator, usable from any other control you can subclass. As is often the case, there are a lot more features you could add to this basic implementation:

Undo
Floating-point support
Button highlights with corresponding key presses
More advanced display, showing current operator, previous values, etc.
More robust handling of overflow

Download Source Code

If you find this article useful, you will love my book, C# 4.0 How-To, which is filled with tips such as this.

Another C# 4.0 How-To Book Give-away

Ben — Fri, 10 Sep 2010 21:18:34 +0000

In celebration of the beginning of the school year here in the USA, I’m going to give away a few more copies of my book C# 4.0 How-To .

If you’ve ever wanted a step-by-step guide with practicable code examples for hundreds of tasks in C#, .Net, and Windows, then this is the book for you. So far, I’m very pleased with the reviews its gotten (if you already have the book and haven’t left a review, why not? )

Just leave a comment on this post, and I’ll choose two people at random. You must be in the US or Canada.

Also, for twitter users, if you retweet a link to this post using the hashtag #cs4howto, I’ll include you in the drawing as well.

The more comments and #cs4howto re-tweets there are, the more books I’ll give away!

Measure Amount of Data to Serialize with a Null Stream

Ben — Mon, 26 Jul 2010 17:00:00 +0000

If you’ve got to serialize some data, especially in a binary format, it’s common to output the length of the data. This is useful for versioning, random access, knowing when you’re done reading the records, among other reasons.

Therefore, you need to know the size of the data you’re going to serialize. There are a few ways to do this:

Measure the position you’re at, write the data, measure the new position, subtract, and that’s your length.
If you want to write the length first (which is usually better), you can write a dummy value, such as 0, then writing the data, then backing up in the stream, and writing the real value.
If you can’t back up the stream (very possible in some situations, or undesirable in others), you can measure the amount of data before you write. However, now you have to maintain that code in addition to the actual serialization.
My solution presented here, avoids having to maintain separate code by writing the data to a null stream which does not write any data, but keeps track of how much data was “written.”

class NullStream : System.IO.Stream
{
    public override bool CanRead { get { return false; } }

    public override bool CanSeek { get { return false; } }

    public override bool CanWrite {get { return true; } }

    public override void Flush() { /*do nothing*/ }

    public override long Length { get { return Position; } }

    private long _position = 0;
    public override long Position
    {
        get
        {
            return _position;
        }
        set
        {
            _position = value;
        }
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
        throw new InvalidOperationException();
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
        Position += count;
    }

    public override long Seek(long offset, System.IO.SeekOrigin origin)
    {
        throw new InvalidOperationException();
    }

    public override void SetLength(long value)
    {
        throw new InvalidOperationException();
    }
}

You can use it like this:

long GetDataSize()
{
    using (NullStream stream = new NullStream())
    {
        if (SaveData(stream))
        {
            return stream.Position;
        }
    }
    return 0;
}

There is a downside to something like this: you’re still essentially doing a lot of the work of serialization. Sure, you’re not writing out the bytes anywhere, but if, say, you need to encode a string as bytes before writing to the stream, that’s still going to happen.

Still, this technique made sense in my case, maybe it will work for you.

C# 4.0 How-To Available Now!

Ben — Mon, 08 Mar 2010 21:41:15 +0000

Well, it’s finally out! Amazon no longer lists the book as available for pre-sale, and it should be shipping to purchasers today or tomorrow. If you’re a B&N shopper, you can also order it there, or grab it in stores within a few days.

From the product description:

Real Solutions for C# 4.0 Programmers

Need fast, robust, efficient code solutions for Microsoft C# 4.0? This book delivers exactly what you’re looking for. You’ll find more than 200 solutions, best-practice techniques, and tested code samples for everything from classes to exceptions, networking to XML, LINQ to Silverlight. Completely up-to-date, this book fully reflects major language enhancements introduced with the new C# 4.0 and .NET 4.0. When time is of the essence, turn here first: Get answers you can trust and code you can use, right now!

Beginning with the language essentials and moving on to solving common problems using the .NET Framework, C# 4.0 How-To addresses a wide range of general programming problems and algorithms. Along the way is clear, concise coverage of a broad spectrum of C# techniques that will help developers of all levels become more proficient with C# and the most popular .NET tools.

Fast, Reliable, and Easy to Use!

Write more elegant, efficient, and reusable code
Take advantage of real-world tips and best-practices advice
Create more effective classes, interfaces, and types
Master powerful data handling techniques using collections, serialization, databases, and XML
Implement more effective user interfaces with both WPF and WinForms
Construct Web-based and media-rich applications with ASP.NET and Silverlight
Make the most of delegates, events, and anonymous methods
Leverage advanced C# features ranging from reflection to asynchronous programming
Harness the power of regular expressions
Interact effectively with Windows and underlying hardware
Master the best reusable patterns for designing complex programs

I’ll be doing a book giveaway at some point as well, once I get my own shipment. Stay tuned!

Get it from Amazon

Get it from Barnes and Noble

How to position windows correctly at 120 DPI in WPF

Ben — Sun, 22 Nov 2009 07:13:52 +0000

If you want to place a window at a specific place in WPF, it will work pretty much as you expect—unless your DPI is 120 (the default is 96). Here’s a sample that shows how to put it where you want.

In this case, I want to put a window just under another control, aligned to its left side.

CalcWindow calc = new CalcWindow();

Point point = this.PointToScreen(

    new Point(0, this.ActualHeight));

PresentationSource source =

    PresentationSource.FromVisual(control);

double dpiX =

    96.0 * source.CompositionTarget.TransformToDevice.M11;

double dpiY =

    96.0 * source.CompositionTarget.TransformToDevice.M22;

calc.Left = point.X * 96.0 / dpiX;

calc.Top = point.Y * 96.0 / dpiY;

calc.Show();

The crux of this is getting the current DPI. You could use P/Invoke to call native methods to get this, but the transformation matrix contains the same information as well.

A WPF Numeric Entry Control

Ben — Mon, 16 Nov 2009 17:00:00 +0000

For my solution I wanted something that behaved very similarly to the WinForms NumericUpdown control.

Some of the specifications:

Allows user to set Value, MaxValue, MinValue, Increment, and LargeIncrement.
Text directly entered is limited to numbers
Pasted text is not intercepted, but when the control has lost focus it will be validated and reset to the previous value if necessary
Two buttons, for increment and decrement
Holding down the buttons with the mouse causes the number to increment continuously
Up and down increment and decrement by Interval
Page Up and Page Down increment and decrement by LargeInterval
This version only supports integers

Creating the control

To begin, create a new WPF project and add a new User Control called NumericEntryControl. This will create a pair of .cs and .xaml files.

In the XAML file, change the root element to be a .


    x:Class="NumericEntryDemo.NumericEntryControl"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
    mc:Ignorable="d"
    xmlns:my="clr-namespace:NumericEntryDemo" Width="200" Height="26">

Before we add the controls, let’s add some properties to our user control to hold the values the controls will use. These are dependency properties in order to take advantage of all the WPF goodness like data binding and animation. Let’s also add standard .Net property wrappers.

public partial class NumericEntryControl : UserControl

    public static readonly DependencyProperty ValueProperty =

        DependencyProperty.Register("Value",

            typeof(Int32), typeof(NumericEntryControl),

            new PropertyMetadata(0));

    public static readonly DependencyProperty MaxValueProperty =

        DependencyProperty.Register("MaxValue",

            typeof(Int32), typeof(NumericEntryControl),

            new PropertyMetadata(100));

    public static readonly DependencyProperty MinValueProperty =

        DependencyProperty.Register("MinValue",

            typeof(Int32), typeof(NumericEntryControl),

            new PropertyMetadata(0));

    public static readonly DependencyProperty IncrementProperty =

        DependencyProperty.Register("Increment",

            typeof(Int32), typeof(NumericEntryControl),

            new PropertyMetadata(1));

    public static readonly DependencyProperty LargeIncrementProperty =

        DependencyProperty.Register("LargeIncrement",

            typeof(Int32), typeof(NumericEntryControl),

            new PropertyMetadata(5));

    public Int32 Value

get

            return (Int32)GetValue(ValueProperty);

set

            SetValue(ValueProperty, value);

    public Int32 MaxValue

get

            return (Int32)GetValue(MaxValueProperty);

set

            SetValue(MaxValueProperty, value);

    public Int32 MinValue

get

            return (Int32)GetValue(MinValueProperty);

set

            SetValue(MinValueProperty, value);

    public Int32 Increment

get

            return (Int32)GetValue(IncrementProperty);

set

            SetValue(IncrementProperty, value);

    public Int32 LargeIncrement

get

            return (Int32)GetValue(LargeIncrementProperty);

set

            SetValue(LargeIncrementProperty, value);

Creating an incrementing TextBox

Add a TextBox inside the and bind its text to the value we created in our control:

<DockPanel d:LayoutOverrides="Width">

    <TextBox

        x:Name="_textbox"

        Margin="2,0"

        Text="{Binding Value,

            Mode=TwoWay,

            RelativeSource={RelativeSource FindAncestor,

                AncestorLevel=1,

                AncestorType={x:Type my:NumericEntryControl}},

            UpdateSourceTrigger=PropertyChanged}"

        HorizontalAlignment="Stretch"

        HorizontalContentAlignment="Right"

        VerticalContentAlignment="Center" />

DockPanel>

This will create a TextBox that sizes itself with its parent (a feature I wanted, but is not strictly necessary) and its text will be bound to the Value in our UserControl.

Handling text input

It used to be that you pointed with a mouse and entered text with a keyboard. However, it is common now to enter text with a stylus, gestures, or some future method not invented yet. Thankfully, WPF supports generic text input handling so you don’t have to concern yourself with the specific hardware.

public NumericEntryControl()

   InitializeComponent();

   _textbox.PreviewTextInput +=

        new TextCompositionEventHandler(_textbox_PreviewTextInput);

void _textbox_PreviewTextInput(object sender,

                   TextCompositionEventArgs e)

    if (!IsNumericInput(e.Text))

        e.Handled = true;

        return;

private bool IsNumericInput(string text)

    foreach (char c in text)

        if (!char.IsDigit(c))

            return false;

    return true;

This prevents anything except numbers from being entered, whether via character recognition or keyboard. It does not, however, prevent the user from pasting non-numeric text into the box. We’ll handle that later.

Validating Text input

It’s problematic to validate and correct user input as they are entering it. For example, if you set the MaxValue to 100, then every time you enter 1000, it jumps to 100, it can be jarring. It’s a similar situation with text pasted into the control. What the NumericUpDown control does is handle these sort of situations when the control loses focus.

To prepare for this, when the control gains focus, we need to save the last valid value so we have something to restore to.

When the control loses focus, we need to first verify that it is a number and if so, clip it to the bounds of our MinValue and MaxValue. If anything fails, set it back to the previous value.

public partial class NumericEntryControl : UserControl

    private int _previousValue = 0;

    public NumericEntryControl()

        InitializeComponent();

        _textbox.PreviewTextInput +=

            new TextCompositionEventHandler(

                _textbox_PreviewTextInput);

        _textbox.GotFocus +=

            new RoutedEventHandler(_textbox_GotFocus);

        _textbox.LostFocus +=

            new RoutedEventHandler(_textbox_LostFocus);

    void _textbox_GotFocus(object sender, RoutedEventArgs e)

        _previousValue = Value;

    void _textbox_LostFocus(object sender, RoutedEventArgs e)

        int newValue = 0;

        if (Int32.TryParse(_textbox.Text, out newValue))

            if (newValue > MaxValue)

                newValue = MaxValue;

            else if (newValue < MinValue)

                newValue = MinValue;

        else

            newValue = _previousValue;

        _textbox.Text = newValue.ToString();

Handle arrow keys

Just because WPF can handle text input from a variety of sources in a hardware-agnostic way doesn’t mean we should ignore the particular strengths of the keyboard. Specifically, we should handle the up and down arrows.

public NumericEntryControl()

...

    _textbox.PreviewKeyDown +=

        new KeyEventHandler(_textbox_PreviewKeyDown);

void _textbox_PreviewKeyDown(object sender, KeyEventArgs e)

    switch (e.Key)

        case Key.Up:

            IncrementValue();

            break;

        case Key.Down:

            DecrementValue();

            break;

        case Key.PageUp:

            Value = Math.Min(Value + LargeIncrement, MaxValue);

            break;

        case Key.PageDown:

            Value = Math.Max(Value - LargeIncrement, MinValue);

            break;

        default:

            //do nothing

            break;

private void IncrementValue()

    Value = Math.Min(Value + Increment, MaxValue);

private void DecrementValue()

    Value = Math.Max(Value - Increment, MinValue);

IncrementValue() and DecrementValue() are pulled out as their own method because they’re used in the button-handling code as well (see below).

The code so far is a perfectly usable textbox that accepts only numbers and can be incremented using the keyboard. Typically, however, we also need to support the mouse, and for that we need buttons (unless you want to do something exotic like programs like Photoshop and Lightroom do, where text boxes have support for incrementing gestures—that’s another article).

A button you can hold down

Adding buttons to increment once per click is pretty easy, but we really want to be able to hold down the buttons and have the TextBox increment. Let’s start by adding the XAML for the buttons:

<UserControl

    x:Class="NumericEntryDemo.NumericEntryControl"

    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"

    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"

    mc:Ignorable="d"

    xmlns:my="clr-namespace:NumericEntryDemo"

    Width="200" Height="26"

    <DockPanel d:LayoutOverrides="Width">

        <Button x:Name="buttonDecrement"

                DockPanel.Dock="Left"

                Content="-"

                Width="{Binding ActualHeight,

                    ElementName=buttonDecrement, Mode=Default}"

                Height="{Binding ActualHeight,

                    ElementName=_textbox, Mode=Default}"/>

        <Button x:Name="buttonIncrement"

                DockPanel.Dock="Right"

                Content="+"

                Width="{Binding ActualHeight,

                    ElementName=buttonDecrement, Mode=Default}"

                Height="{Binding ActualHeight,

                    ElementName=_textbox, Mode=Default}"/>

        <TextBox

            x:Name="_textbox"

            Margin="2,0"

            Text="{Binding Value,

                Mode=TwoWay,

                RelativeSource={RelativeSource FindAncestor,

                    AncestorLevel=1,

                    AncestorType={x:Type my:NumericEntryControl}},

                UpdateSourceTrigger=PropertyChanged}"

            HorizontalAlignment="Stretch"

            HorizontalContentAlignment="Right"

            VerticalContentAlignment="Center" />

    DockPanel>

UserControl>

Note that the button Width property is bound to its own ActualHeight property, and the Height property is bound to the TextBox’s ActualHeight. This has the effect of keeping the buttons square, the same height as the TextBox. It’s an effect I wanted, but you can easily dispose of it. With these buttons, our control finally takes shape:

How fast should we increment?

Before writing the code to do the incrementing as we hold the button down, it’s worth considering how fast the incrementing should occur. Ideally, we would want it to increment at about the same rate as if we were holding down the up key on the keyboard. The keyboard repeat rate is an operating system value that we can retrieve.

There are actually two values:

private static int _delayRate =

    System.Windows.SystemParameters.KeyboardDelay;

private static int _repeatSpeed =

    Math.Max(1, System.Windows.SystemParameters.KeyboardSpeed);

The delay rate is how long we should wait before starting the repetition, and is given in multiples of 250ms. Roughly speaking, humans can determine and control actions with lengths of time of about 200ms, so 250ms is a good value to start with. Any shorter and the repetition might start when it was not intended (say, if they just click the button instead of holding it down).

The keyboard speed is the number of times per second we should repeat—sort of. The value can be 0, so because of the way I use it below I want to sure it’s at least 1.

To allow us to hold the button down, we need to override the default mouse handling of a button which is to disable the standard LeftMouseButtonDown/Up messages. Instead, we need to handle the PreviewMouseLeftButtonDown message and its corresponding Up message.

When we handle the down message, we need to set a timer for the keyboard delay value. When we handle the timer’s tick, we need to increment (or decrement) and change the timer’s interval to the repeat speed. This repeat speed is calculated merely by dividing 1000ms (1s) by the rate per second. There may be better ways, but this gets pretty close to the rate experienced by the keyboard on my computer. Finally, when the mouse button is released we need to stop the timer. We also do a final increment, which will cover the case where the user clicks instead of holds.

We also need to capture the mouse in case the user moves it off the button—otherwise the timer will just keep incrementing forever.

Here’s the code:

private DispatcherTimer _timer =

    new DispatcherTimer();

private static int _delayRate =

    System.Windows.SystemParameters.KeyboardDelay;

private static int _repeatSpeed =

    Math.Max(1, System.Windows.SystemParameters.KeyboardSpeed);

private bool _isIncrementing = false;

public NumericEntryControl()

...

    buttonIncrement.PreviewMouseLeftButtonDown +=

        new MouseButtonEventHandler(

            buttonIncrement_PreviewMouseLeftButtonDown);

    buttonIncrement.PreviewMouseLeftButtonUp +=

        new MouseButtonEventHandler(

            buttonIncrement_PreviewMouseLeftButtonUp);

    buttonDecrement.PreviewMouseLeftButtonDown +=

        new MouseButtonEventHandler(

            buttonDecrement_PreviewMouseLeftButtonDown);

    buttonDecrement.PreviewMouseLeftButtonUp +=

        new MouseButtonEventHandler(

            buttonDecrement_PreviewMouseLeftButtonUp);

    _timer.Tick += new EventHandler(_timer_Tick);

void buttonIncrement_PreviewMouseLeftButtonDown(

    object sender, MouseButtonEventArgs e)

    buttonIncrement.CaptureMouse();

    _timer.Interval =

        TimeSpan.FromMilliseconds(_delayRate * 250);

    _timer.Start();

    _isIncrementing = true;

void buttonIncrement_PreviewMouseLeftButtonUp(

    object sender, MouseButtonEventArgs e)

    _timer.Stop();

    buttonIncrement.ReleaseMouseCapture();

    IncrementValue();

void buttonDecrement_PreviewMouseLeftButtonDown(

    object sender, MouseButtonEventArgs e)

    buttonDecrement.CaptureMouse();

    _timer.Interval =

        TimeSpan.FromMilliseconds(_delayRate * 250);

    _timer.Start();

    _isIncrementing = false;

void buttonDecrement_PreviewMouseLeftButtonUp(

    object sender, MouseButtonEventArgs e)

    _timer.Stop();

    buttonDecrement.ReleaseMouseCapture();

    DecrementValue();

void _timer_Tick(object sender, EventArgs e)

    if (_isIncrementing)

        IncrementValue();

    else

        DecrementValue();

    _timer.Interval =

        TimeSpan.FromMilliseconds(1000.0 / _repeatSpeed);

And voila! A NumericEntryControl that’s basic and easy-to-use for both keyboard and mouse.

Further improvements

This isn’t the last word in numeric entry controls, by any means. There are many ways to accomplish it, and this is one that worked well for me. There are a number of further enhancements you could do (and perhaps should do):

More validation
Ensure that MaxValue >= MinValue
Set focus to the TextBox when the control gains focus (maybe)
Define strokes to increment and decrement with a stylus
The user can change the keyboard repeat rate through Control Panel. This program could be modified to listen for updates to this value.

There’s also another, really cool feature that I will add to this in a future post.

Download full source.

Found this article helpful? Want a resource of hundreds of similar, how-to tips? I’ve written a book that covers topics like this and more in C# 4. Check out C# 4.0 How-To!

Updated CPU usage article

Ben — Wed, 04 Feb 2009 19:44:49 +0000

I made a important changes to the CPU usage code and have updated the article to reflect it. Instead of a critical section, the code uses just the interlocked increment/decrement functions. I also updated the sample demo to use multiple threads to read the CPU usage to demonstrate the thread safety clearly.

Determine CPU usage of current process (C++ and C#)

Ben — Sat, 03 Jan 2009 18:31:34 +0000

My first book, C# 4.0 How-To is now shipping! If you like tips you can use, check it out!

Updated 2/4/2009: I changed the implementation of these classes from the original:

Instead of a critical section, InterlockedIncrement/Decrement is used.
The sample driver program now demos using multiple threads using the CpuUsage class to show thread safety.

Download the C++ and C# projects that accompany this article.

Just to make it clear, there is no API called GetProcessCpuPercentage(). To find out the percentage, we can use some other, real APIs and do some calculations. Before getting to the equation and code, let’s discuss the different types of time available.

There are four types of time:

Wall time – The actual, real-world progression of time as measured by you on your watch.
Kernel time – The amount of time spent in kernel mode (protected, high-order mode of operation)
User time – the amount of time spent in user-mode (often by the process itself)
Idle time – nothing going on at all

Kernel, User, and Idle sum to total time, which is approximately wall-time.

Each process spends some time in kernel mode and some time in user mode. We just need to compare the time spent by a process to the time spent by all processes on the computer, since the last time we made such a measurement. It is important to note that we do NOT take into account the idle time.

Thus, the equation is

There are two APIs that are useful:

GetProcessTimes – Get times for a specific process
GetSystemTimes – Get total times for the entire system (all CPUs)

The times reported are absolute, so what we are actually interested is in the difference between the current times and those from a previous run.

Armed with this information, we can calculate the CPU usage for the current process (or any arbitrary process, for that matter).

Let’s do it first in C++ to demonstrate usage of the APIs.

CPU Usage Percentage in C++

Here’s the header file:

   1: #pragma once

   2: #include

3:

   4: class CpuUsage

   5: {

   6: public:

   7:     CpuUsage(void);

8:

   9:     short  GetUsage();

  10: private:

  11:     ULONGLONG SubtractTimes(const FILETIME& ftA, const FILETIME& ftB);

  12:     bool EnoughTimePassed();

  13:     inline bool IsFirstRun() const { return (m_dwLastRun == 0); }

14:

  15:     //system total times

  16:     FILETIME m_ftPrevSysKernel;

  17:     FILETIME m_ftPrevSysUser;

18:

  19:     //process times

  20:     FILETIME m_ftPrevProcKernel;

  21:     FILETIME m_ftPrevProcUser;

22:

  23:     short m_nCpuUsage;

  24:     ULONGLONG m_dwLastRun;

25:

  26:     volatile LONG m_lRunCount;

  27: };

The GetUsage() method is where the work occurs. The other methods are to help in the calculations. The critical section run count enables the code to be called in a multi-threaded environment without problems. I also prevent the code from being called more often than every 250ms. Here is the complete implementation:

   1: #include "StdAfx.h"

   2: #include

   3: #include "CpuUsage.h"

4:

   5: CpuUsage::CpuUsage(void)

   6: :m_nCpuUsage(-1)

   7: ,m_dwLastRun(0)

   8: ,m_lRunCount(0)

   9: {

  10:     ZeroMemory(&m_ftPrevSysKernel, sizeof(FILETIME));

  11:     ZeroMemory(&m_ftPrevSysUser, sizeof(FILETIME));

12:

  13:     ZeroMemory(&m_ftPrevProcKernel, sizeof(FILETIME));

  14:     ZeroMemory(&m_ftPrevProcUser, sizeof(FILETIME));

15:

  16: }

17:

18:

  19: /**********************************************

  20: * CpuUsage::GetUsage

  21: * returns the percent of the CPU that this process

  22: * has used since the last time the method was called.

  23: * If there is not enough information, -1 is returned.

  24: * If the method is recalled to quickly, the previous value

  25: * is returned.

  26: ***********************************************/

  27: short CpuUsage::GetUsage()

  28: {

  29:     //create a local copy to protect against race conditions in setting the

  30:     //member variable

  31:     short nCpuCopy = m_nCpuUsage;

  32:     if (::InterlockedIncrement(&m_lRunCount) == 1)

  33:     {

  34:         /*

  35:         If this is called too often, the measurement itself will greatly

  36:         affect the results.

  37:         */

38:

  39:         if (!EnoughTimePassed())

  40:         {

  41:             ::InterlockedDecrement(&m_lRunCount);

  42:             return nCpuCopy;

  43:         }

44:

  45:         FILETIME ftSysIdle, ftSysKernel, ftSysUser;

  46:         FILETIME ftProcCreation, ftProcExit, ftProcKernel, ftProcUser;

47:

  48:         if (!GetSystemTimes(&ftSysIdle, &ftSysKernel, &ftSysUser) ||

  49:             !GetProcessTimes(GetCurrentProcess(), &ftProcCreation,

  50:                 &ftProcExit, &ftProcKernel, &ftProcUser))

  51:         {

  52:             ::InterlockedDecrement(&m_lRunCount);

  53:             return nCpuCopy;

  54:         }

55:

  56:         if (!IsFirstRun())

  57:         {

  58:             /*

  59:             CPU usage is calculated by getting the total amount of time

  60:             the system has operated since the last measurement

  61:             (made up of kernel + user) and the total

  62:             amount of time the process has run (kernel + user).

  63:             */

  64:             ULONGLONG ftSysKernelDiff =

  65:                 SubtractTimes(ftSysKernel, m_ftPrevSysKernel);

  66:             ULONGLONG ftSysUserDiff =

  67:                 SubtractTimes(ftSysUser, m_ftPrevSysUser);

68:

  69:             ULONGLONG ftProcKernelDiff =

  70:                 SubtractTimes(ftProcKernel, m_ftPrevProcKernel);

  71:             ULONGLONG ftProcUserDiff =

  72:             SubtractTimes(ftProcUser, m_ftPrevProcUser);

73:

  74:             ULONGLONG nTotalSys =  ftSysKernelDiff + ftSysUserDiff;

  75:             ULONGLONG nTotalProc = ftProcKernelDiff + ftProcUserDiff;

76:

  77:             if (nTotalSys > 0)

  78:             {

  79:                 m_nCpuUsage = (short)((100.0 * nTotalProc) / nTotalSys);

  80:             }

  81:         }

82:

  83:         m_ftPrevSysKernel = ftSysKernel;

  84:         m_ftPrevSysUser = ftSysUser;

  85:         m_ftPrevProcKernel = ftProcKernel;

  86:         m_ftPrevProcUser = ftProcUser;

87:

  88:         m_dwLastRun = GetTickCount64();

89:

  90:         nCpuCopy = m_nCpuUsage;

  91:     }

92:

  93:     ::InterlockedDecrement(&m_lRunCount);

94:

  95:     return nCpuCopy;

  96: }

97:

  98: ULONGLONG CpuUsage::SubtractTimes(const FILETIME& ftA, const FILETIME& ftB)

  99: {

 100:     LARGE_INTEGER a, b;

 101:     a.LowPart = ftA.dwLowDateTime;

 102:     a.HighPart = ftA.dwHighDateTime;

 103:

 104:     b.LowPart = ftB.dwLowDateTime;

 105:     b.HighPart = ftB.dwHighDateTime;

 106:

 107:     return a.QuadPart - b.QuadPart;

 108: }

 109:

 110: bool CpuUsage::EnoughTimePassed()

 111: {

 112:     const int minElapsedMS = 250;//milliseconds

 113:

 114:     ULONGLONG dwCurrentTickCount = GetTickCount64();

 115:     return (dwCurrentTickCount - m_dwLastRun) > minElapsedMS;

 116: }

In order to test this, here is a simple program that starts two threads that run an infinite loop, eating the processor. On a dual-core system, this process will take roughly 85-95% of the CPU. I also start two threads to access the usage object and poll the CPU usage in order to demonstrate the thread safety of the object.

   1: // CpuUsageCpp.cpp : Defines the entry point for the console application.

   2: //

3:

   4: #include "stdafx.h"

   5: #include

   6: #include "CpuUsage.h"

7:

   8: DWORD WINAPI EatItThreadProc(LPVOID lpParam);

   9: DWORD WINAPI WatchItThreadProc(LPVOID lpParam);

10:

  11: CpuUsage usage;

12:

  13: int _tmain(int argc, _TCHAR* argv[])

  14: {

  15:     //start threads to eat the processor

  16:     CreateThread(NULL, 0, EatItThreadProc, NULL, 0, NULL);

  17:     CreateThread(NULL, 0, EatItThreadProc, NULL, 0, NULL);

18:

  19:     //start threads to watch the processor (to test thread-safety)

  20:     CreateThread(NULL, 0, WatchItThreadProc, NULL, 0, NULL);

  21:     CreateThread(NULL, 0, WatchItThreadProc, NULL, 0, NULL);

22:

  23:     while (true)

  24:     {

  25:         Sleep(1000);

  26:     }

27:

  28:     return 0;

  29: }

30:

31:

  32: DWORD WINAPI WatchItThreadProc(LPVOID lpParam)

  33: {

  34:     while (true)

  35:     {

  36:         short cpuUsage = usage.GetUsage();

37:

  38:         printf("Thread id %d: %d%% cpu usage\n", ::GetCurrentThreadId(), cpuUsage);

  39:         Sleep(1000);

  40:     }

  41: }

42:

  43: DWORD WINAPI EatItThreadProc(LPVOID lpParam)

  44: {

  45:     ULONGLONG accum = 0;

  46:     while (true)

  47:     {

  48:         accum++;

  49:     }

50:

  51:     printf("%64d\n", accum);

  52: }

C# Version

In C#, The System.Diagnostics.Process can give us the time information for a specific process. However, we still need the Win32 API call for getting the total system times (GetSystemTimes). The Process class reports times in TimeSpans, not FILETIME, so our class is modified accordingly.

   1: using System;using System.Collections.Generic;

   2: using System.Linq;

   3: using System.Text;

   4: using System.Runtime.InteropServices;

   5: using ComTypes = System.Runtime.InteropServices.ComTypes;

   6: using System.Threading;

   7: using System.Diagnostics;

8:

   9: namespace CpuUsageCs

  10: {

  11:     class CpuUsage

  12:     {

  13:         [DllImport("kernel32.dll", SetLastError = true)]

  14:         static extern bool GetSystemTimes(

  15:                     out ComTypes.FILETIME lpIdleTime,

  16:                     out ComTypes.FILETIME lpKernelTime,

  17:                     out ComTypes.FILETIME lpUserTime

  18:                     );

19:

  20:         ComTypes.FILETIME _prevSysKernel;

  21:         ComTypes.FILETIME _prevSysUser;

22:

  23:         TimeSpan _prevProcTotal;

24:

  25:         Int16 _cpuUsage;

  26:         DateTime _lastRun;

  27:         long _runCount;

28:

  29:         public CpuUsage()

  30:         {

  31:             _cpuUsage = -1;

  32:             _lastRun = DateTime.MinValue;

  33:             _prevSysUser.dwHighDateTime = _prevSysUser.dwLowDateTime = 0;

  34:             _prevSysKernel.dwHighDateTime = _prevSysKernel.dwLowDateTime = 0;

  35:             _prevProcTotal = TimeSpan.MinValue;

  36:             _runCount = 0;

  37:         }

38:

  39:         public short GetUsage()

  40:         {

  41:             short cpuCopy = _cpuUsage;

  42:             if (Interlocked.Increment(ref _runCount) == 1)

  43:             {

  44:                 if (!EnoughTimePassed)

  45:                 {

  46:                     Interlocked.Decrement(ref _runCount);

  47:                     return cpuCopy;

  48:                 }

49:

  50:                 ComTypes.FILETIME sysIdle, sysKernel, sysUser;

  51:                 TimeSpan procTime;

52:

  53:                 Process process = Process.GetCurrentProcess();

  54:                 procTime = process.TotalProcessorTime;

55:

  56:                 if (!GetSystemTimes(out sysIdle, out sysKernel, out sysUser))

  57:                 {

  58:                     Interlocked.Decrement(ref _runCount);

  59:                     return cpuCopy;

  60:                 }

61:

  62:                 if (!IsFirstRun)

  63:                 {

  64:                     UInt64 sysKernelDiff =

  65:                         SubtractTimes(sysKernel, _prevSysKernel);

  66:                     UInt64 sysUserDiff =

  67:                         SubtractTimes(sysUser, _prevSysUser);

68:

  69:                     UInt64 sysTotal = sysKernelDiff + sysUserDiff;

70:

  71:                     Int64 procTotal = procTime.Ticks - _prevProcTotal.Ticks;

72:

  73:                     if (sysTotal > 0)

  74:                     {

  75:                         _cpuUsage = (short)((100.0 * procTotal) / sysTotal);

  76:                     }

  77:                 }

78:

  79:                 _prevProcTotal = procTime;

  80:                 _prevSysKernel = sysKernel;

  81:                 _prevSysUser = sysUser;

82:

  83:                 _lastRun = DateTime.Now;

84:

  85:                 cpuCopy = _cpuUsage;

  86:             }

  87:             Interlocked.Decrement(ref _runCount);

88:

  89:             return cpuCopy;

90:

  91:         }

92:

  93:         private UInt64 SubtractTimes(ComTypes.FILETIME a, ComTypes.FILETIME b)

  94:         {

  95:             UInt64 aInt =

  96:             ((UInt64)(a.dwHighDateTime << 32)) | (UInt64)a.dwLowDateTime;

  97:             UInt64 bInt =

  98:             ((UInt64)(b.dwHighDateTime << 32)) | (UInt64)b.dwLowDateTime;

99:

 100:             return aInt - bInt;

 101:         }

 102:

 103:         private bool EnoughTimePassed

 104:         {

 105:             get

 106:             {

 107:                 const int minimumElapsedMS = 250;

 108:                 TimeSpan sinceLast = DateTime.Now - _lastRun;

 109:                 return sinceLast.TotalMilliseconds > minimumElapsedMS;

 110:             }

 111:         }

 112:

 113:         private bool IsFirstRun

 114:         {

 115:             get

 116:             {

 117:                 return (_lastRun == DateTime.MinValue);

 118:             }

 119:         }

 120:     }

 121: }

These classes can now be used wherever you need to monitor the CPU usage of a process.

Notice any improvements to be made? Leave a comment.

Download C++ and C# projects

My first book, C# 4.0 How-To is now shipping! If you like tips you can use, check it out!

An easy stack layout panel for WinForms

Ben — Fri, 12 Dec 2008 04:52:51 +0000

This is a simple, but useful tip. Users of WPF are spoiled. They have all sorts of layout options. Those of us still working in WinForms have FlowLayoutPanel and TableLayoutPanel. That’s it. WPF has those and more.

For my current project, I needed a panel to layout controls vertically. The TableLayoutPanel can be awkward to work with, at least for what I need it to. At first glance, the FlowLayoutPanel looks it won’t work, since it produces something like this:

That’s with changing the FlowDirection to TopDown and putting AutoScroll to true.

But what I want is this:

To achieve this layout, merely set all the following properties on a FlowLayoutPanel:

AutoScroll = True
FlowDirection = TopDown
WrapContents = False

et voilà, Instant stack panel.

Converting OLE_COLOR to System.Drawing.Color

Ben — Sun, 14 Sep 2008 03:45:42 +0000

I’ve been working on a project using Visual Studio Tools for Office 2008 (VSTO) and at one point I needed to get the colors for categories in Outlook 2007. There are actually 3 colors, and they are returned as uint’s–why the .Net wrappers don’t convert to colors for you, I don’t know (to avoid linking to System.Drawing?).

The important thing is to convert them into the friendly System.Drawing.Color objects I know and love. For this task, there exists a handy ColorTranslator class. There is a FromOle method that does the exact chore you need. Here’s a sample of my code:

private void GetCategoryColors()
{
    foreach (OutlookLib.Category category in
        Application.ActiveExplorer().Session.Categories)
    {
        CategoryColor color = new CategoryColor(
            ColorTranslator.FromOle((Int32)category.CategoryGradientTopColor),
            ColorTranslator.FromOle((Int32)category.CategoryGradientBottomColor),
            ColorTranslator.FromOle((Int32)category.CategoryBorderColor));
        _categoryCollection[category.Name] = color;
    }
}

Tracking database changes using triggers

Ben — Tue, 13 May 2008 12:00:53 +0000

Tracking changes in database tables is an incredibly useful feature–especially for operational data that can change often. Having recently had to implement this feature, I thought I’d share some of the techniques I learned.

Sample Database

First, let’s conceptualize a very simple database consisting of user information (name, date of birth), and e-mails. A user can have more than one e-mail.

Table: UserData

Field	Type
ID	int (PK, identitiy)
FirstName	varchar
LastName	varchar
birthdate	date

Table: UserEmails

Field	Type
UserID	int (FK)
email	varchar

We want to track all changes to the FirstName, LastName, and birthdate fields. In addition we want to track when e-mails are added or removed from a user. As we’ll see, these aims are accomplished using two different methods.

My implementation is done in SQL Server 2000 and C#, but any database that supports triggers can be used.

Changes in a Single Table

With this method we want to track the changes to all fields of a table. In our example, we want to know when FirstName, LastName, and birthdate change values in the UserData table.

To accomplish this we need another table to track the history. This table is going to have the exact same fields as UserData, plus a few extra for the change tracking.

Table: UserDataChanges

Field	Type
ChangeID	int (PK, identity)
ChangeTime	datetime
ChangeUser	varchar
ID	int (FK)
FirstName	varchar
LastName	varchar
birthdate	date

Now the automated part–adding a trigger to populate this automatically:

CREATE TRIGGER UserDataChangeTrigger ON UserData FOR UPDATE, INSERT
AS    
    IF (UPDATE (FirstName) OR UPDATE(LastName) OR UPDATE(birthdate))    
    BEGIN     
        INSERT UserDataChanges 
            (ChangeTime, ChangeUser, ID, FirstName, LastName, birthdate)
            (SELECT GetUtcDate(), user, ID, FirstName,LastName,birthdate 
                FROM inserted)     
    END     

This trigger will insert a new row into the UserDataChanges table whenever a row in the UserData table is updated or inserted. The IF (UPDATE(FirstName)…. ) is not strictly required in this scenario, but in other cases I did not want a change recorded when certain fields were updated (i.e., you have a field that tracks the last change time of that row, or the number of orders, or any other field that can change frequently and isn’t important to track–you don’t want to create too much noise in this or it will not be useful). The GetUtcDate() and user are SQL Server functions that retrieve the current UTC time and the username of the process that caused the change–very useful for tracking responsibility. The inserted table is created by the server for use by the trigger and contains all the new values.

Changes in a Foreign Key Table

The UserEmails has to be handled differently because there can be multiple e-mails for each user and we can assume they can be added, or removed at will (Remove + Add = Update, so I won’t consider direct updates here).

The solution I landed on was to have a generic event log table that stores manual log entries as well as “special” entries denoting adding or removing e-mails.

Table: UserEventLog

Field	Type
EventID	int (PK, identity)
ID	int (FK)
EventTime	datetime
EventType	int
ChangeUser	varchar
Notes	varchar

This table can be used for both adding text notes to a user and, by using the EventType field, special events. In our example, we have two events we need to track:

Event	Value
EmailAdded	1
EmailRemoved	2

(In code, I’ve made these enumerations)

Next we add a trigger on the UserEmails table:

CREATE TRIGGER UserEmails_EmailAddedTrigger
ON UserEmails
FOR INSERT
AS
 BEGIN
     INSERT UserEventLog(ID, EventTime, EventType, ChangeUser, Notes)
        (SELECT ID, GetUtcDate(), 1, user, '{'+email+'}' FROM inserted)
 END

The value 1 stands for EmailAdded. I’ve added braces around the actual e-mail address to set it apart from regular notes (we’ll see how to integrate everything later).

To handle the deletion of e-mails add another trigger:

CREATE TRIGGER UserEmails_EmailRemovedTrigger
ON UserEmails
FOR DELETE
AS
 BEGIN
     INSERT UserEventLog(ID, EventTime, EventType, ChangeUser, Notes )
        (SELECT ID, GetUtcDate(), 2, user, '{'+email+'}' FROM deleted)
 END

The only things different: FOR DELETE (instead of INSERT), changed the EventType to 2 (EmailRemoved), and the values are taken from the SQL Server-supplied deleted table.

That’s enough to get a pretty good change-tracking system in place, but you’ll still have to build a UI to display it effectively.

Displaying the Changes in the UI

With the above work done, you end up with two types of entities: changes and events. While it would be possible to integrate all functionality into a single event/change table using a lot more logic in the SQL Trigger code, I’m personally more comfortable with the change logic being in my application code. I think this way the database is kept more “pure” and open to changes down the line.

That means we will need to integrate these two types of entities into a single list, ordered by date/time. I’m going to assume the existence of two classes or structs that represent each of these entities. They’ll be called UserChange and UserEvent. I’ll also assume that the lists of each of these are already sorted by time, since that’s trivial to do in a SQL query.

Given that, we need a function that takes both of these lists and produces a sorted, combined list with an easy-to-understand list.

How the function works:

Go through both lists, and pick whichever one is next, time-wise.
Translate the object into a string/list-view representation of that object.
If it’s a UserChange object, compare it to the previous one to figure out what changed.
Sort the list in reverse order to put newer items at the top.

Here’s the C# code which I’ve adapted from our production system. Don’t get hung up on the details:

private void FillLog(IList events, IList changes)

    List tempItems = new List();

    int currentEventIdx = 0;

    int currentChangeIdx = 0;

    eventLogListView1.Items.Clear();

    while (currentEventIdx < events.Count

    || currentChangeIdx < changes.Count)

    UserChange currentChange = null;

    UserChange prevChange = null;

    UserEvent currentEvent = null;

    DateTime changeTime = DateTime.MaxValue;

    DateTime eventTime = DateTime.MaxValue;

    if (currentChangeIdx < changes.Count)

        currentChange = changes[currentChangeIdx];

        changeTime = currentChange.ChangeDate;

        if (currentChangeIdx > 0)

        prevChange = changes[currentChangeIdx - 1];

    if (currentEventIdx < events.Count)

        currentEvent = events[currentEventIdx];

        eventTime = currentEvent.EventDate;

    string dateStr;

    string userStr;

    string eventTypeStr="";

    string notesStr;

    if (changeTime < eventTime)

        dateStr = Utils.FormatDateTime(changeTime);

        userStr = currentChange.UserName;

        notesStr = GetChangeString(currentChange, prevChange);

        currentChangeIdx++;

    else

        dateStr = Utils.FormatDate(eventTime);

        userStr = currentEvent.UserName;

        notesStr = currentEvent.Notes;

        eventTypeStr = currentEvent.EventType.ToString();

        currentEventIdx++;

    if (notesStr.Length > 0)

        ListViewItem item = new ListViewItem(dateStr);

        item.SubItems.Add(userStr);

        item.SubItems.Add(eventTypeStr);

        item.SubItems.Add(notesStr);

        item.ToolTipText = notesStr;

        item.BackColor = (tempItems.Count % 2 == 0) ?

            Color.Wheat : Color.White;

        tempItems.Add(item);

    }//end while

    eventLogListView1.BeginUpdate();

    for (int i = tempItems.Count - 1; i >= 0; i--)

    eventLogListView1.Items.Add(tempItems[i]);

    eventLogListView1.AutoResizeColumn(0,

        ColumnHeaderAutoResizeStyle.ColumnContent);

    eventLogListView1.AutoResizeColumn(1,

        ColumnHeaderAutoResizeStyle.ColumnContent);

    eventLogListView1.AutoResizeColumn(2,

        ColumnHeaderAutoResizeStyle.ColumnContent);

    eventLogListView1.Columns[3].Width = eventLogListView1.Width -

    (eventLogListView1.Columns[0].Width +

    eventLogListView1.Columns[1].Width +

    eventLogListView1.Columns[2].Width +10);

    eventLogListView1.EndUpdate();

Now we need to define GetChangeString, which figures out the differences in successive UserChange objects and displays only pertinent information.

private string GetChangeString(

    BuoyDataChange currentChange,

    BuoyDataChange prevChange)

    StringBuilder sb = new StringBuilder();

    if (prevChange == null)

        CompareAndAdd(sb, "First Name",

            null, currentChange.FirstName);

        CompareAndAdd(sb, "Last Name",

            null, currentChange.LastName);

        CompareAndAdd(sb, "Birth Date",

            null, currentChange.BirthDate);

    else

        CompareAndAdd(sb, "First Name",

            prevChange.FirstName, currentChange.FirstName);

        CompareAndAdd(sb, "Last Name",

            prevChange.LastName, currentChange.LastName);

        CompareAndAdd(sb, "Birth Date",

            prevChange.BirthDate, currentChange.BirthDate);

    return sb.ToString();

And one last helper function which compares two objects and if different appends the change to a StringBuilder object.

private void CompareAndAdd(StringBuilder sb, string field,

    object oldVal, object newVal)

       if (oldVal == null && newVal == null)

           return;

       if (oldVal == null || !oldVal.Equals(newVal))

           if (sb.Length > 0)

               sb.Append(", ");

           sb.AppendFormat("{0}:{1} -> {2}", field, oldVal, newVal);

In this way you can end up with an automated system that displays all changes in an easy-to-understand format.

Here’s a sample of what our system looks like (click to enlarge):

Other ways to accomplish this? Better ways? Please leave a comment!

In this universe we obey the law of commutativity

Ben — Thu, 17 Apr 2008 12:43:55 +0000

This kind of thing has happened to be a few times now, so I thought I’d share the fun.

In one of our pieces of software we have a process that looks like this:

void MyThread()
{
    while (true)
    {
        DoFunctionA();
        DoFunctionB();
        SleepFor10Seconds();
    }
    
}

While FunctionA and FunctionB are conceptually similar, they interact with completely different systems.

We had a problem with FunctionA the other day–it was taking 120 seconds to do its thing instead of the normal 10 (or less) because a remote server was down. This caused problems for FunctionB because it wasn’t running as often as it should have so things were getting backed up in the system. Oops.

Now, the solution is to split these two functions into two independent threads so they don’t interfere with each other, and I’ve been meaning to do this for a while, so that’s what I proposed.

Response back: “That’s a good idea, but before we do something complicated like that, can we just put FunctionB first?“

Um, no.

The time we want to minimize is the time between running FunctionB, which is Time_Sleep + Time_A. Putting FunctionB first makes it Time_A + Time_Sleep. Last I checked, those were actually equivalent.

GetTextExtent vs. DrawText (with DT_CALCRECT)

Ben — Thu, 10 Apr 2008 18:35:44 +0000

Working on an MFC app that has just been converted to Unicode (finally!), I noticed that one button (which is created dynamically) is too small to fit the text in Korean (and Russian and a few other languages).

The code was calling something like:

CSize sz = m_btAdjustColors.GetDC()->GetTextExtent(sCaption);

It seems correct, but these script languages are throwing it for a loop–the measured size is much smaller than it should be. The GetTextExtent documentation doesn’t shed any explicit light on this subject, but may hint at it.

The solution? DrawText. There is a flag you can pass to tell it to calculate the rectangle needed instead of drawing.

CRect rect(0,0,0,0);
m_btAdjustColors.GetDC()->DrawText(sCaption, &rect, DT_CALCRECT);

It’s important to initialize the rectangle to zeroes because, as the docs say, it only modifies the right and bottom members of the rectangle.

How to file good bug reports (from Frank Kelly)

Ben — Wed, 19 Mar 2008 14:41:39 +0000

This is an issue I run into constantly at my job.

Frank Kelly wrote up a good summary of some items. They’re simple, easy to understand, easy to follow, even for non-programmers.

In fact, I’m sending this link out to everyone in my group here at work.

Technorati Tags: testing,programming,bug reporting

Never make assumptions about performance

Ben — Mon, 17 Mar 2008 13:47:54 +0000

The importance of measuring performance changes is a topic that has been covered by others smarter and more experienced than me, but I have a recent simple tale.

I’ve simplified the code quite a bit in order to demonstrate the issue. Suppose I have a wrapper around an image (it has many more attributes):

   1: class Picture

   2: {

   3:     Image _image;

   4:     string _path;

5:

   6:     public Image Photo

   7:     {

   8:         get

   9:         {

  10:             if (_image==null && !string.IsNullOrEmpty(_path))

  11:             {

  12:                 _image = Bitmap.FromFile(_path);

  13:             }

  14:             return _image;

  15:         }

  16:     }

17:

  18: }

I had this and a view that loading about 2,700 of these into a customized ListView control at program startup. On a cold start (where none of the pictures were in the disk’s cache), it would take 27 seconds. Unacceptable.

What to do?

My first thought was to load the pictures asynchronously. I wrapped Bitmap.FromFile() into a function and called it asynchronously. When it was done, it fired an event that percolated up to the top.

Well, I spent about 30 minutes implementing that and ran it–horrible. The list showed up immediately, but it was unusable. The problem? Dumping 2,700 items into the ThreadPool queue is a problem. It doesn’t create 2,700 threads, but it causes enough problems to not be a viable option.

Asynchronicity is still the answer, though. But it’s at a different level. Instead of loading the individual images asynchronously, I skipped loading the images when creating the list control and instead launched a thread to load all the images and update them when done. The list loads in under a second, and the pictures show up little by little after that.

Measure, measure, measure. And pay attention.

Technorati Tags: code,asynchronous program model,c#

Tip: Easily Automating use of WaitCursor

Ben — Fri, 22 Feb 2008 16:31:25 +0000

This is really simple and probably common, but it’s a useful tip anyway.

Say you need to set a form’s cursor to the wait cursor while you accomplish something.

You would do something like this:

this.Cursor = Cursors.WaitCursor;

//do something

this.Cursor = Cursors.Default;

Of course, what if “do something” throws an exception? Then your cursor won’t be set back to the default.

So let’s wrap it in try-finally.

try

    this.Cursor = Cursors.WaitCursor;

    //do something

finally

    this.Cursor = Cursors.Default;

Better, but that’s a lot of wrapping around a simple operation. Notice, that the try-finally is exactly the pattern that using is. Why not wrap this functionality into a simple to use class that handles the cursor reset automatically?

internal class WaitCursor : IDisposable

    private Control _control = null;

    public WaitCursor(Control control)

        _control = control;

        _control.Cursor = Cursors.WaitCursor;

    public void Dispose()

        _control.Cursor = Cursors.Default;

And to use it in a form is simple:

using (new WaitCursor(this))

    //do work

Of course, you could easily add functionality like restoring the previous cursor instead of always the default, handling exceptions, make it thread-aware so it uses Invoke if necessary, better error-handling, etc.

Technorati Tags: C#,.net,Forms,Tip

.Net Reflector

Ben — Wed, 13 Feb 2008 15:58:12 +0000

Lutz Roeder’s .Net Reflector has been discussed on many blogs before, but I want to give it an additional plug. I recently had to emulate some C# serial-port code in our C++ app. The .Net SerialPort class is great, easy-to-use, and works well. Unfortunately, we’re using a C++ serial port library that does not support all the possible features. Fortunately, we have the source code and can easily extend it. Unfortunately, I’m not too familiar with serial port programming, and the .Net functionality does not all obviously map to the Win32 API in every respect.

Enter Reflector. It was trivial to poke into the .Net assemblies and see what the SerialPort class was doing under the covers and then use the correct Win32 functionality in our app.

There are also a ton of plugins available.

Technorati Tags: reflector,.net,c++,C#

Solving "Unexpected Store Error" in Exchange

Ben — Wed, 30 Jan 2008 16:52:41 +0000

Getting a weird COM Exception with the cryptic ID 0x8055001E?

We’ve been struggling with this problem for over a year now, and we finally have a solution.

We have some critical code that is contacting Exchange server via COM Interop and CDOEX.DLL to read some inboxes and process e-mails. About once a month or so, we get this error:

System.Runtime.InteropServices.COMException (0x8055001E): Unexpected

store error: %1!d! (0x%1!8.8x!)

   at ADODB.RecordsetClass.Open(Object Source, Object

ActiveConnection, CursorTypeEnum CursorType, LockTypeEnum LockType,

Int32 Options)

   at MessageService.Exchange.ExchangeClient.Connect(String folderUrl,

String userId, String password, Boolean useHttp)

After this point, restarting our software does not help. The only recourse is to restart the Exchange store completely. Did I mention that our software needs to run 24/7/365 with no downtime (a few minutes here and there are acceptable)?

So about once a month, I get a message on my phone, I log into the server, reboot Exchange, and all is well.

Searching on Google revealed nothing at all. Until recently.

I now believe the problem was we were checking two e-mail accounts back-to-back, in a loop like this (highly simplified):

while (running)

    CheckAccount1();

    CheckACcount2();

    Thread.Sleep(60000);

Apparently, there is some bug in the CDO COM components’ code that will cause errors if you reconnect too fast. Occasionally, the Exchange code must have completed so quickly that it didn’t provide enough time for the COM components to clean up properly before the next solution attempt. Solution?

while (running)

    CheckAccount1();

    Thread.Sleep(5000);

    CheckAccount2();

    Thread.Sleep(60000);

We implemented that change on a staging server that was also experiencing this problem and haven’t had a single reoccurrence since. The fix will be going into production very soon. No more 2AM alerts!

Easily Unit Testing Event Handlers

Ben — Fri, 28 Dec 2007 01:48:32 +0000

In C#, If you need to unit test a class that fires an event in certain circumstances (perhaps even asynchronously), you need to handle a little more than just running some code and doing the assertion. You have to make sure your unit test waits for the event to be fired. Here’s one naive way of doing it, a WRONG way:

   1: private bool statsUpdated = false;

   2: private ManualResetEvent statsUpdatedEvent = new ManualResetEvent(false);

3:

   4: [Test]

   5: public void CheckStats()

   6: {

   7:     BrickDatabase db = new BrickDatabase(tempFolder, maxCacheAge);

8:

   9:     statsUpdated = false;

  10:     statsUpdatedEvent.Reset();

11:

  12:     db.InventoryStatsUpdated += new EventHandler(db_InventoryStatsUpdated);

  13:     db.DoSomethingThatFiresEvent();

14:

  15:     statsUpdatedEvent.WaitOne();

16:

  17:     Assert.IsTrue(statsUpdated);

  18: }

19:

  20: void db_InventoryStatsUpdated(object sender, EventArgs e)

  21: {

  22:     statsUpdated = true;

  23:     statsUpdatedEvent.Set();

  24: }

There are a number of things wrong with this:

The class variables. More complex unit test class. Have to coordinate these variables across multiple functions.
Since they are class variables, you will want to reuse them, but you’d better remember to reset the event and the boolean every time!
Have to have two functions to do something really, really simple.
The WaitOne() does not have a timeout, so if the wait is ever satisfied then statsUpdated is guaranteed to be true.

Here’s a better way of doing it, using anonymous methods in C# 2.0:

   1: [Test]

   2: public void CheckStats()

   3: {

   4:     BrickDatabase db = new BrickDatabase(tempFolder, maxCacheAge);

   5:     bool statsUpdated = false;

   6:     ManualResetEvent statsUpdatedEvent = new ManualResetEvent(false);

7:

   8:     db.InventoryStatsUpdated += delegate

   9:     {

  10:         statsUpdated = true;

  11:         statsUpdatedEvent.Set();

  12:     };

13:

  14:     db.DoSomethingThatFiresEvent();

15:

  16:     statsUpdatedEvent.WaitOne(5000,false);

17:

  18:     Assert.IsTrue(statsUpdated);

  19: }

Improvements?

The event is just part of the method. Since the event handler is an anonymous delegate, it can access the enclosing method’s local variables.
Added 5,000ms timeout to the WaitOne() function to prevent hanging of unit tests.

Technorati Tags: event handling, C#, anonymous delegates

DiskSlicer 1.2 Out

Ben — Tue, 18 Dec 2007 02:12:33 +0000

I made some minor updates to DiskSlicer. Mostly, some minor bug fixes, but also I added the much-requested ability to delete files directly from the program.

Go get it and enjoy!