UIElement.PreviewMouseLeftButtonDown Event
Definition
Important
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Occurs when the left mouse button is pressed while the mouse pointer is over this element.
public:
virtual event System::Windows::Input::MouseButtonEventHandler ^ PreviewMouseLeftButtonDown;public event System.Windows.Input.MouseButtonEventHandler PreviewMouseLeftButtonDown;member this.PreviewMouseLeftButtonDown : System.Windows.Input.MouseButtonEventHandler Public Custom Event PreviewMouseLeftButtonDown As MouseButtonEventHandler Event Type
Implements
Remarks
Although this routed event seems to follow a tunneling route through an element tree, it actually is a direct routed event that is raised and reraised along the element tree by each UIElement.
This event is one of several related events that report the mouse-button specifics of an underlying Mouse.PreviewMouseDown event, which is an attached event that is processed by each element along an event route.
The event data of this event exposes the event data of the underlying Mouse.PreviewMouseDown event. If that event is marked as handled along the event route, the mouse-button specific events are still raised; however, handlers of the mouse-button specific events must be added by explicitly calling AddHandler, with the option to handle events that are already marked as handled, in order to be listeners to the event. If you mark PreviewMouseLeftButtonDown handled, you are essentially marking Mouse.PreviewMouseDown handled for all further listeners along the route, and on all related events. This possibly includes class-handler generated events such as PreviewMouseDoubleClick.
Conceptually, think of this event (and other mouse-button events on UIElement) to be a mouse "service" (with the service definition provided by the Mouse class). The event adds the convenience of not needing to check the mouse button states (left-right, up-down) of the original mouse events in the event data. For more advanced scenarios, such as checking for states of non-standard buttons, you might need to use the APIs on the Mouse class rather than those on UIElement.
Routed Event Information
| Identifier field | PreviewMouseLeftButtonDownEvent |
| Routing strategy | Direct |
| Delegate | MouseButtonEventHandler |
- Override OnPreviewMouseLeftButtonDown to implement class handling for this event in derived classes.
