Andy (Steve) De George
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title, ms.date, dev_langs, helpviewer_keywords, ms.assetid
| title | ms.date | dev_langs | helpviewer_keywords | ms.assetid | ||||
|---|---|---|---|---|---|---|---|---|
| How to: Handle a Routed Event | 03/30/2017 |
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157787b4-f469-4047-8777-5b034145f32e |
How to: Handle a Routed Event
This example shows how bubbling events work and how to write a handler that can process the routed event data.
Example
In Windows Presentation Foundation (WPF), elements are arranged in an element tree structure. The parent element can participate in the handling of events that are initially raised by child elements in the element tree. This is possible because of event routing.
Routed events typically follow one of two routing strategies, bubbling or tunneling. This example focuses on the bubbling event and uses the xref:System.Windows.Controls.Primitives.ButtonBase.Click?displayProperty=nameWithType event to show how routing works.
The following example creates two xref:System.Windows.Controls.Button controls and uses XAML attribute syntax to attach an event handler to a common parent element, which in this example is xref:System.Windows.Controls.StackPanel. Instead of attaching individual event handlers for each xref:System.Windows.Controls.Button child element, the example uses attribute syntax to attach the event handler to the xref:System.Windows.Controls.StackPanel parent element. This event-handling pattern shows how to use event routing as a technique for reducing the number of elements where a handler is attached. All the bubbling events for each xref:System.Windows.Controls.Button route through the parent element.
Note that on the parent xref:System.Windows.Controls.StackPanel element, the xref:System.Windows.Controls.Primitives.ButtonBase.Click event name specified as the attribute is partially qualified by naming the xref:System.Windows.Controls.Button class. The xref:System.Windows.Controls.Button class is a xref:System.Windows.Controls.Primitives.ButtonBase derived class that has the xref:System.Windows.Controls.Primitives.ButtonBase.Click event in its members listing. This partial qualification technique for attaching an event handler is necessary if the event that is being handled does not exist in the members listing of the element where the routed event handler is attached.
[!code-xamlRoutedEventHandle#XAML]
The following example handles the xref:System.Windows.Controls.Primitives.ButtonBase.Click event. The example reports which element handles the event and which element raises the event. The event handler is executed when the user clicks either button.
[!code-csharpRoutedEventHandle#Handler] [!code-vbRoutedEventHandle#Handler]