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ContentElement.OnPreviewMouseLeftButtonDown Method

Invoked when an unhandled PreviewMouseLeftButtonDown routed event reaches an element in its route that is derived from this class. Implement this method to add class handling for this event.

Namespace:  System.Windows
Assembly:  PresentationCore (in PresentationCore.dll)

protected internal virtual void OnPreviewMouseLeftButtonDown(
	MouseButtonEventArgs e
)

Parameters

e
Type: System.Windows.Input.MouseButtonEventArgs
The MouseButtonEventArgs that contains the event data. The event data reports that the left mouse button was pressed.

The PreviewMouseLeftButtonDown event appears to travel a tunneling route but actually travels in an indirect way. Mouse.PreviewMouseDown is the underlying event that is tunnel routed, and each ContentElement along the event route uses identical handling to raise the direct routed event PreviewMouseLeftButtonDown. Although you can mark the PreviewMouseLeftButtonDown event as handled for purposes of this element, the handled state does not perpetuate to other elements along the event route. However, you might want to mark the event as handled in order to prevent general instance handlers (those that did not specify handledEventsToo) from being invoked.

The default implementation for general mouse event handling in ContentElement listens for Mouse.PreviewMouseDown and converts it to an appropriate local event. If you want to override this logic, you must create a derived class. In the static constructor of your derived class, register an alternative class handler for Mouse.PreviewMouseDown. You cannot change the mouse handling behavior of ContentElement by overriding OnPreviewMouseLeftButtonDown.

Alternatively, you can override this method in order to change event handling for a specific mouse state. Whether you choose to call the base implementation depends on your scenario. Failing to call base disables default input handling for that mouse event on ancestor classes that also expect to invoke OnPreviewMouseLeftButtonDown. For example, you can derive from Button and override OnPreviewMouseLeftButtonDown in your derived class without calling the base implementation; however, this override disables the Click event.

.NET Framework

Supported in: 4, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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