Question

I am trying to emulate click events in Swing using following code:

event = new MouseEvent(target, MouseEvent.MOUSE_PRESSED, ...)
java.awt.Toolkit.getDefaultToolkit().getSystemEventQueue().postEvent(event);
event = new MouseEvent(target, MouseEvent.MOUSE_RELEASED, ...)
java.awt.Toolkit.getDefaultToolkit().getSystemEventQueue().postEvent(event);
event = new MouseEvent(target, MouseEvent.MOUSE_CLICKED, ...)
java.awt.Toolkit.getDefaultToolkit().getSystemEventQueue().postEvent(event);

This works fine for most components, but the problem is if component is generating it’s own events, for example if when component receives MOUSE_PRESSED it generates some events and submits them with dispatchEvent(newEvent); With normal click event order would be:

MOUSE_PRESSED
newEvent
MOUSE_RELEASED
MOUSE_CLICKED

But because of my code order is:

MOUSE_PRESSED    
MOUSE_RELEASED
MOUSE_CLICKED
newEvent

And it breaks application logic. I can easily fix it by adding Thread.sleep() calls between my postEvent() calls, but I don’t want to do it since this method is called a lot and I don’t want it to be slow, especially since current code works in 95% of cases.

How would I emulate event sequence allowing new events to be created between them? I don’t have access to component code, so I can only modify my emulation method.

Answer 1

You could push your own event queue which would give you total control of events. For example:

    class SchedulingEventQueue extends EventQueue
    {
      // Use Map< AWTEvent, List< AWTEvent > > to support multiple events
      private final Map< AWTEvent, AWTEvent > eventSchedule = new HashMap< AWTEvent, AWTEvent >();

      public void scheduleEvent( final AWTEvent event, final AWTEvent dependentEvent )
      {
        eventSchedule.put( dependentEvent, event );
      }

      @Override
      protected void dispatchEvent( final AWTEvent event )
      {
        try
        {
          super.dispatchEvent( event );
        }
        finally
        {
          // Dispatch any dependent event
          AWTEvent scheduledEvent = eventSchedule.remove( event );
          if( scheduledEvent != null )
          {
            postEvent( scheduledEvent );
          }
        }
      }
    }

    // Now the code to post the events becomes:
    {
      SchedulingEventQueue eventQueue = new SchedulingEventQueue();

      Toolkit.getDefaultToolkit().getSystemEventQueue().push( eventQueue );

      MouseEvent pressEvent = new MouseEvent(target, MouseEvent.MOUSE_PRESSED, ...)
      MouseEvent releaseEvent = new MouseEvent(target, MouseEvent.MOUSE_RELEASED, ...)
      MouseEvent clickEvent = new MouseEvent(target, MouseEvent.MOUSE_CLICKED, ...)

      eventQueue.scheduleEvent( clickEvent, releaseEvent );
      eventQueue.scheduleEvent( releaseEvent, pressEvent );
      eventQueue.postEvent( pressEvent );
    }

You just chain the events together so that they don’t get posted until the previous event has been dispatched allowing any intermediate events created by a component to be posted during dispatch before your next event is posted. I haven’t tried this but it should work.