C# 4 and .NET 4

736 ❘ ChaPTer 27 COre xAml
public static readonly DependencyProperty ValueProperty =
DependencyProperty.Register("Value", typeof(int), typeof(MyDependencyObject),
new PropertyMetadata(0, OnValueChanged, CoerceValue));
//...
}
}
private static void OnValueChanged(DependencyObject obj,
DependencyPropertyChangedEventArgs args)
{
int oldValue = (int)args.OldValue;
int newValue = (int)args.NewValue;
//...
}
code snippet DependencyObjectDemo/MyDependencyObject.cs
bubbling and Tunneling eVenTs
Elements can be contained in elements. With XAML and WPF, you can defi ne that a Button contains a
ListBox ; the ListBox contains items that are Button controls again. When you click on an inner control,
the event should go all the way to the outside. WPF supports bubbling and tunneling events. Often these
events are used in pairs. The PreviewMouseMove event is a tunneling event that tunnels from the outside to
the inside. MouseMove follows the PreviewMouseMove event and is a bubbling event that bubbles from the
inside to the outside.
Core information about .NET events is explained in Chapter 8, “ Delegates, Lambdas,
and Events.”
To demonstrate bubbling, the following XAML code contains four Button controls where the surrounding
StackPanel defi nes an event handler for the Button.Click event named OnOuterButtonClick() .
button2 contains a ListBox that has two Button controls as its children and the Click event handler
OnButton2() . Both of the inner buttons also have an event handler associated with the Click event.
< Window x:Class=" Wrox.ProCSharp.XAML.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525" >
< StackPanel x:Name="stackPanel1" Button.Click="OnOuterButtonClick" >
< Button x:Name="button1" Content="Button 1" Margin="5" / >
< Button x:Name="button2" Margin="5" Click="OnButton2" >
< ListBox x:Name="listBox1" >
< Button x:Name="innerButton1" Content="Inner Button 1" Margin="4"
Padding="4" Click="OnInner1" / >
< Button x:Name="innerButton2" Content="Inner Button 2" Margin="4"
Padding="4" Click="OnInner2" / >
< /ListBox >
< /Button >
< ListBox ItemsSource="{Binding}" / >
< /StackPanel >
< /Window >
code snippet BubbleDemo/MainWindow.xaml
www.it-ebooks.info