ToolStripDropDownItem.DropDownOpening 事件


ToolStripDropDown 正在打开时发生。Occurs as the ToolStripDropDown is opening.

 event EventHandler ^ DropDownOpening;
public event EventHandler DropDownOpening;
member this.DropDownOpening : EventHandler 
Public Custom Event DropDownOpening As EventHandler 


下面的代码示例演示如何使用此成员。The following code example demonstrates the use of this member. 在此示例中, 事件处理程序报告DropDownOpening事件的发生。In the example, an event handler reports on the occurrence of the DropDownOpening event. 此报表可帮助你了解何时发生事件, 并可帮助你进行调试。This report helps you to learn when the event occurs and can assist you in debugging. 若要报告多个事件或频繁发生的事件, 请考虑MessageBox.ShowConsole.WriteLine消息替换为多行或将TextBox其追加到多行。To report on multiple events or on events that occur frequently, consider replacing MessageBox.Show with Console.WriteLine or appending the message to a multiline TextBox.

若要运行示例代码,请将其粘贴到一个项目中,该项目包含从ToolStripDropDownItem继承的类型的实例,如ToolStripDropDownButton ToolStripMenuItem或。To run the example code, paste it into a project that contains an instance of a type that inherits from ToolStripDropDownItem, such as a ToolStripMenuItem or ToolStripDropDownButton. 然后命名该实例ToolStripDropDownItem1 ,并确保事件处理程序DropDownOpening与事件相关联。Then name the instance ToolStripDropDownItem1 and ensure that the event handler is associated with the DropDownOpening event.

private void ToolStripDropDownItem1_DropDownOpening(Object sender, EventArgs e) {

   MessageBox.Show("You are in the ToolStripDropDownItem.DropDownOpening event.");

Private Sub ToolStripDropDownItem1_DropDownOpening(sender as Object, e as EventArgs) _ 
     Handles ToolStripDropDownItem1.DropDownOpening

   MessageBox.Show("You are in the ToolStripDropDownItem.DropDownOpening event.")

End Sub


有关处理事件的详细信息, 请参阅处理和引发事件For more information about handling events, see Handling and Raising Events.