How to: Position a Custom Context Menu in a RichTextBox
This example shows how to position a custom context menu for a RichTextBox.
When you implement a custom context menu for a RichTextBox, you are responsible for handling the placement of the context menu. By default, a custom context menu is opened at the center of the RichTextBox.
For a working sample that demonstrate this example, see Position a Custom Context Menu in a RichTextBox Sample.
Example
To override the default placement behavior, add a listener for the ContextMenuOpening event. The following example shows how to do this programmatically.
richTextBox.ContextMenuOpening += new ContextMenuEventHandler(richTextBox_ContextMenuOpening);
The following example shows an implementation the corresponding ContextMenuOpening event listener.
// 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;
}