avalonia-events

Avalonia Routed Events

Overview

Avalonia uses routed events that travel the logical tree. Three strategies:

• Bubble — source → root (default for most input events)
• Tunnel — root → source (Preview prefix by convention)
• Direct — only raised on source element

All input events (PointerPressed, KeyDown, etc.) are routed.

Handling Events

XAML:

<Button Click="Button_Click"/>
<StackPanel PointerPressed="Panel_PointerPressed"/>

Code-behind (direct +=):

myButton.Click += Button_Click;
private void Button_Click(object? sender, RoutedEventArgs e) { }

AddHandler — explicit routing strategy, required for tunneling:

// Catch bubbled clicks from any child Button
myPanel.AddHandler(Button.ClickEvent, OnAnyButtonClick, RoutingStrategies.Bubble);

// Intercept before children see it (tunneling)
myPanel.AddHandler(InputElement.PointerPressedEvent, OnPreviewPointerPressed,
    RoutingStrategies.Tunnel);

private void OnAnyButtonClick(object? sender, RoutedEventArgs e)
{
    Console.WriteLine($"Clicked: {e.Source}");
}

Remove handler:

myPanel.RemoveHandler(Button.ClickEvent, OnAnyButtonClick);

Stopping Propagation

private void OnKeyDown(object? sender, KeyEventArgs e)
{
    if (e.Key == Key.Escape)
    {
        e.Handled = true; // stops further bubbling/tunneling
    }
}

e.Handled = true prevents subsequent handlers in the route from firing.

Defining Custom Routed Events

public class MyControl : Control
{
    // Event registration
    public static readonly RoutedEvent<RoutedEventArgs> ActivatedEvent =
        RoutedEvent.Register<MyControl, RoutedEventArgs>(
            name: "Activated",
            routingStrategy: RoutingStrategies.Bubble);

    // CLR event wrapper
    public event EventHandler<RoutedEventArgs> Activated
    {
        add => AddHandler(ActivatedEvent, value);
        remove => RemoveHandler(ActivatedEvent, value);
    }

    // Raise it
    protected void RaiseActivated()
        => RaiseEvent(new RoutedEventArgs(ActivatedEvent, this));
}