UIElement.OnDragEnter(DragEventArgs) 方法


當未處理的 DragEnter 附加事件到達其路由中衍生自此類別的項目時叫用。Invoked when an unhandled DragEnter attached event reaches an element in its route that is derived from this class. 實作這個方法可為此事件加入類別處理。Implement this method to add class handling for this event.

 virtual void OnDragEnter(System::Windows::DragEventArgs ^ e);
protected virtual void OnDragEnter (System.Windows.DragEventArgs e);
abstract member OnDragEnter : System.Windows.DragEventArgs -> unit
override this.OnDragEnter : System.Windows.DragEventArgs -> unit
Protected Overridable Sub OnDragEnter (e As DragEventArgs)



包含事件資料的 DragEventArgsThe DragEventArgs that contains the event data.


這個方法沒有預設的實值。This method has no default implementation. 因為繼承中的中繼類別可能會執行此方法,所以我們建議您在執行時呼叫基底實作為。Because an intermediate class in the inheritance might implement this method, we recommend that you call the base implementation in your implementation.

這個方法的用途類似于 通用語言執行平台 (CLR)common language runtime (CLR) * 方法上的事件模式:此方法提供的方法,是藉由建立類別處理常式,而不是實例處理常式,來處理衍生類別的相符事件。The purpose of this method is similar to the 通用語言執行平台 (CLR)common language runtime (CLR) event pattern On* methods: this method provides the means to handle the matching event from derived classes by establishing a class handler instead of an instance handler. 在此情況下,比對事件是路由事件。In this case the matching event is a routed event. On * 方法的真實模式與路由事件不同,因為路由事件可以由子項目引發,這不一定是將叫用處理程式的元素。The implementation pattern of the On* methods is different for routed events because a routed event can be raised by a child element, which is not necessarily the element that will invoke handlers. 因此,您的執行必須檢查事件資料的來源屬性。Therefore, your implementation needs to examine the source properties of the event data. 在大部分情況下,它不應該嘗試 reraise 事件。It should not try to reraise the event in most cases.

藉由覆寫這個方法或向註冊類別處理常式 RegisterClassHandler ,的衍生類別 UIElement 可以在事件路由收到事件時呼叫私用類別處理常式方法。Either by overriding this method or by registering class handlers with RegisterClassHandler, derived classes of UIElement can call private class handler methods when the event is received along the event route. 適當類別處理的其中一個情況是操作事件資料,並將路由事件標示為已處理。One scenario where class handling is appropriate is to manipulate the event data and mark the routed event as handled.