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.

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;
}
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