When I show a popup menu at the mouse cursor's position it often goes off screen when the cursor is near the right or bottom border.

Created May 4, 2012

Jan Borchers

This seems to be a little bug in Swing. The position of a popup menu is not 'auto-adjusted' by Swing.

You'll have to show the popup menu. Then check the menu's location against the screen's boundaries and move the menu if needed.

For example, suppose we have the following code in a MouseListener that invokes the popup:


public void mouseReleased(MouseEvent event)
{
  if(event.isPopupTrigger()){

    // show popup menu
    menu.show((Component)event.getSource(), 
              event.getX(), event.getY());

    // determine boundaries
    Point point = menu.getLocationOnScreen();
    Dimension size = menu.getSize();
    Rectangle oldRect = 
      new Rectangle(point.x, point.y, size.width, size.height);

    // helper function to move oldRect completely
    // onto screen (desktop) if necessary
    Rectangle newRect = ensureRectIsVisible(oldRect);

    // rects differ, need moving
    if(!oldRect.equals(newRect)){
      Window window = SwingUtilities.getWindowAncestor(menu);
      if(window != null){
        window.setLocation(newRect.x, newRect.y);
      }
    }
  }
}

// helper function to move a rectangle onto the screen
private Rectangle ensureRectIsVisible(Rectangle bounds)
{
  Dimension size = Toolkit.getDefaultToolkit().getScreenSize();

  return new Rectangle(Math.max(0, 
                                Math.min(size.width - bounds.width,
                                         bounds.x)),
                       Math.max(0, 
                                Math.min(size.height - bounds.height, 
                                         bounds.y)),
                       bounds.width,
                       bounds.height);
}