Event bubbling or event routing

WPF introduces EventBubbling. People who have done scripting in Internet Explorer will find this very familiar. The concept is that an eventhandler may not be implemented on a GUI-control, but can also be implemented on the parent of that GUI-control. When an event is fired it will traverse the tree from child to parent to parent to parent until it reaches the top control, usually the window.

Let's look at a demo.

Below is the XAML file for Window1.

<Window x:Class="Demo3.EventHandling.Window1"
    xmlns="http://schemas.microsoft.com/winfx/avalon/2005"
    xmlns:x="http://schemas.microsoft.com/winfx/xaml/2005"
    Title="Demo3.EventHandling"
    >
    <Grid>
    <Button VerticalAlignment="Stretch" Click="button1_Click" 
            HorizontalAlignment="Stretch" Grid.Column="0" Grid.ColumnSpan="1" 
            Grid.Row="0" Grid.RowSpan="1" Margin="80,85,77,121" 
            Width="NaN" Height="NaN" Name="button1">
      <StackPanel Orientation="Vertical">
        <Image Source="C:\Documents and Settings\Mark\Desktop\banner.jpg" Name="image1"/>
        <TextBox Name="textbox1" Text="Type your name here!" Height="20" Width="333" />
        <Button Name="innerButton" Click="innerButton_Click">Press me!</Button>
      </StackPanel>
    </Button>
  </Grid>
</Window>

Here is the code.

void button1_Click(object sender, RoutedEventArgs e)
{
    MessageBox.Show("Hello " + this.textbox1.Text);
    Button source = e.OriginalSource as Button;
    if (source != null)
    {
        MessageBox.Show("The original source is: " + source.Name);
    }
}

void innerButton_Click(object sender, RoutedEventArgs e)
{
    MessageBox.Show("Hello SDN!");
}

This will look like:

Just click on the various controls. Notice that controls that do not have a 'Click' event do not participate in the routing, but may still pass the event on.

In WPF this concept is called event routing. You can halt the routing of an event by setting

e.Halted = true;