如何：在 RichTextBox 中定位自定义上下文菜单
更新：2007 年 11 月
本示例演示如何定位 RichTextBox 的自定义上下文菜单。
实现 RichTextBox 的自定义上下文菜单时，应负责处理上下文菜单的定位。 默认情况下，自定义上下文菜单是在 RichTextBox 中心打开的。
有关对此示例进行演示的有效示例，请参见在 RichTextBox 中定位自定义上下文菜单的示例。
示例
若要重写默认定位行为，应当为 ContextMenuOpening 事件添加一个侦听器。 下面的示例演示如何以编程方式实现此目的。
richTextBox.ContextMenuOpening += new ContextMenuEventHandler(richTextBox_ContextMenuOpening);
下面的示例演示对应 ContextMenuOpening 事件侦听器的实现。
// This method is intended to listen for the ContextMenuOpening event from a RichTextBox.
// It will position the custom context menu at the end of the current selection.
void richTextBox_ContextMenuOpening(object sender, ContextMenuEventArgs e)
{
// Sender must be RichTextBox.
RichTextBox rtb = sender as RichTextBox;
if (rtb == null) return;
ContextMenu contextMenu = rtb.ContextMenu;
contextMenu.PlacementTarget = rtb;
// This uses HorizontalOffset and VerticalOffset properties to position the menu,
// relative to the upper left corner of the parent element (RichTextBox in this case).
contextMenu.Placement = PlacementMode.RelativePoint;
// Compute horizontal and vertical offsets to place the menu relative to selection end.
TextPointer position = rtb.Selection.End;
if (position == null) return;
Rect positionRect = position.GetCharacterRect(LogicalDirection.Forward);
contextMenu.HorizontalOffset = positionRect.X;
contextMenu.VerticalOffset = positionRect.Y;
// Finally, mark the event has handled.
contextMenu.IsOpen = true;
e.Handled = true;
}