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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.

To override the default placement behavior, add a listener for the ContextMenuOpening event. The following example shows how to do this programmatically.

			AddHandler richTextBox.ContextMenuOpening, AddressOf 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.
		Private Sub richTextBox_ContextMenuOpening(ByVal sender As Object, ByVal e As ContextMenuEventArgs)
			' Sender must be RichTextBox.
			Dim rtb As RichTextBox = TryCast(sender, RichTextBox)
			If rtb Is Nothing Then
				Return
			End If

			Dim contextMenu As 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.
			Dim position As TextPointer = rtb.Selection.End

			If position Is Nothing Then
				Return
			End If

			Dim positionRect As Rect = position.GetCharacterRect(LogicalDirection.Forward)
			contextMenu.HorizontalOffset = positionRect.X
			contextMenu.VerticalOffset = positionRect.Y

			' Finally, mark the event has handled.
			contextMenu.IsOpen = True
			e.Handled = True
		End Sub
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