source: trunk/src_apollo/org/apollo/mvc/SwingEventQueue.java@ 315

package org.apollo.mvc;

import java.util.LinkedList;
import java.util.Queue;

import javax.swing.SwingUtilities;

/**
 * If your observer needs to reacts to events on the swing thread (i.e. interacting with swing
 * objects somewhere in the event) and the observed subject raised events on other threads,
 * this class thunnels all events into the swing thread and ensures that they are raised in
 * the swing thread (thread safety!).
 * 
 * @author Brook Novak
 *
 */
public class SwingEventQueue {
        
        private SwingThreadedObserver target;

        // Using a FIFO queue implementation
        private Queue<QueudEvent> eventQueue = new LinkedList<QueudEvent>();
        
        private EventProccessor eventProccessor = new EventProccessor();
        
        /**
         * COnstructor.
         * @param target The SwingThreadedObserver instance to thunnel events to on the swing thread.
         */
        public SwingEventQueue(SwingThreadedObserver target) {
                if (target == null) throw new NullPointerException("target");
                this.target = target;
        }

        /**
         * Adds an event to the wing queue. The event will be re-fired on the swing thread
         * and raised on the target.
         * 
         * @param event A type of SubjectChangedEvent
         * @param source The subject which the event was fired from
         */
        public synchronized void queueEvent(Subject source, SubjectChangedEvent event) {
                synchronized (eventQueue) {
                        eventQueue.add(new QueudEvent(source, event));
                }
                SwingUtilities.invokeLater(eventProccessor);
        }

        class EventProccessor implements Runnable {

                public void run() { // invoked on swing thread

                        synchronized (eventQueue) {
                                while (!eventQueue.isEmpty()) {
                                        QueudEvent qe = eventQueue.remove();
                                        target.modelChangedOnSwingThread(qe.source, qe.event);
                                }
                        }
                }

        }
        
        class QueudEvent {
                public QueudEvent(Subject source, SubjectChangedEvent event) {
                        this.event = event;
                        this.source = source;
                }
                SubjectChangedEvent event;
                Subject source;
        }

}