How to Handle Routed Event From a Child Window

Question

Intention is to get and handle Routed Events from child Window. I cannot (read: do not want to) use direct routing as there are more elements between (a Command).

The following example demonstrates that Event Routing is not working from one Window to second Window. Child window XAML:

<Window x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">
<Grid>
    <Button Content="Raise Routing Event" HorizontalAlignment="Left" Margin="50" VerticalAlignment="Top"
            Width="150" Click="RaiseRoutedEvent" />
</Grid>

Raise Event Code:

using System.Windows;

namespace WpfApplication1
{
    public partial class Window1
    {
        private static readonly RoutedEvent ChildWindowEvent = EventManager.RegisterRoutedEvent("ButtonClicked",
            RoutingStrategy.Bubble, typeof(RoutedEventHandler), typeof(Window1));

        public Window1()
        {
            InitializeComponent();
        }

        public event RoutedEventHandler ButtonClicked
        {
            add { AddHandler(ChildWindowEvent, value); }
            remove { RemoveHandler(ChildWindowEvent, value); }
        }

        private void RaiseRoutedEvent(object sender, RoutedEventArgs e)
        {
            RoutedEventArgs eventArgs = new RoutedEventArgs(ChildWindowEvent);
            RaiseEvent(eventArgs);
        }
    }
}

Main window:

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:wpfApplication1="clr-namespace:WpfApplication1"
        Title="MainWindow" Height="350" Width="525" wpfApplication1:Window1.ButtonClicked="HandleRoutedEvent">
    <Grid>
        <Button Content="Open new window" HorizontalAlignment="Left" Margin="50" VerticalAlignment="Top"
                Width="150" Click="OpenNewWindow" />
    </Grid>
</Window>

Window which should handle the routed event:

using System.Windows;

namespace WpfApplication1
{
    public partial class MainWindow
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void OpenNewWindow(object sender, RoutedEventArgs e)
        {
            Window1 window1 = new Window1();
            window1.ShowDialog();
        }

        private void HandleRoutedEvent(object sender, RoutedEventArgs e)
        {
            MessageBox.Show("This message is shown from the Main Window");
        }
    }
}

The event is raised from Window1 but the MainWindow.HandleRoutedEvent does not hit its break point. Why?

Answer 1

Routed Events travel along the visual tree. A top-level window is a visual tree root and is not part of its owner's visual tree. Therefore, any events which bubble up from within a child window will not propagate up to the owner window.

As an aside, I noticed a couple issues in your example code. In your xaml, you register a handler with attached event syntax, but you have declared an instance event. If you want to implement an attached event, you will need these members:

public static readonly RoutedEvent ButtonClickedEvent = EventManager.RegisterCrossWindowRoutedEvent(
    "ButtonClicked",
    RoutingStrategy.Bubble,
    typeof(RoutedEventHandler),
    typeof(ChildWindow));

public static void AddButtonClickedHandler(UIElement target, RoutedEventHandler handler)
{
    target.AddHandler(ButtonClickedEvent, handler);
}

public static void RemoveButtonClickedHandler(UIElement target, RoutedEventHandler handler)
{
    target.RemoveHandler(ButtonClickedEvent, handler);
}

If you intended to have an instance event, the event name should correspond with the name provided when registering the routed event ("ButtonClicked").