Helper class to periodically run code that updates SWT widgets

PeriodicUIUpdater.java

/***************************************************************************************************
 * Copyright (c) 2014 Rüdiger Herrmann
 * All rights reserved. This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *   Rüdiger Herrmann - initial API and implementation
 **************************************************************************************************/
package com.codeaffine.util;

import static com.google.common.collect.Iterables.toArray;
import static com.google.common.collect.Lists.newLinkedList;

import java.util.Collection;

import org.eclipse.swt.SWT;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Event;
import org.eclipse.swt.widgets.Listener;
import org.eclipse.swt.widgets.Widget;


/**
 * With this helper class, periodic UI updates can be scheduled.
 * <p>
 * This example will update the text if the labels every Minute until the shell gets disposed of.
 * </p>
 * <pre>
 * Shell shell = new Shell( ... );
 * Label label1 = new Label( shell, SWT.NONE );
 * Label label2 = new Label( shell, SWT.NONE );
 * Runnable runnable = new Runnable() {
 *   public void run() {
 *     label1.setText( ... );
 *     label2.setText( ... );
 *   }
 * };
 * PeriodicUIUpdater.registerRunnable( shell, runnable );
 * </pre>
 */
public class PeriodicUIUpdater {

  public static void registerRunnable( Widget widget, Runnable runnable ) {
    forDisplay( widget.getDisplay() ).addRunnable( widget, runnable );
  }

  private static final String DISPLAY_DATA = PeriodicUIUpdater.class.getName();
  static final int TIMER_INTERVAL = 60 * 1000;

  static PeriodicUIUpdater forDisplay( Display display ) {
    PeriodicUIUpdater result = ( PeriodicUIUpdater )display.getData( DISPLAY_DATA );
    if( result == null ) {
      result = new PeriodicUIUpdater( display );
    }
    return result;
  }

  private final Display display;
  private final Runnable timerRunnable;
  private final Collection<Runnable> runnables;

  private PeriodicUIUpdater( Display display ) {
    this.display = display;
    this.display.setData( DISPLAY_DATA, this );
    this.runnables = newLinkedList();
    this.timerRunnable = new TimerRunnable();
    scheduleTimerRunnable();
  }

  void addRunnable( Widget widget, Runnable runnable ) {
    runnables.add( runnable );
    widget.addListener( SWT.Dispose, new WidgetDisposeListener( runnable ) );
  }

  void removeRunnable( Runnable runnable ) {
    runnables.remove( runnable );
    if( runnables.isEmpty() ) {
      dispose();
    }
  }

  void dispose() {
    display.timerExec( -1, timerRunnable );
    display.setData( DISPLAY_DATA, null );
  }

  void updateUI() {
    runRunnables();
    scheduleTimerRunnable();
  }

  private void scheduleTimerRunnable() {
    display.timerExec( TIMER_INTERVAL, timerRunnable );
  }

  private void runRunnables() {
    Runnable[] runnablesCopy = toArray( runnables, Runnable.class );
    for( Runnable runnable : runnablesCopy ) {
      runnable.run();
    }
  }

  class TimerRunnable implements Runnable {
    @Override
    public void run() {
      updateUI();
    }
  }

  private class WidgetDisposeListener implements Listener {
    private final Runnable runnable;

    WidgetDisposeListener( Runnable runnable ) {
      this.runnable = runnable;
    }

    @Override
    public void handleEvent( Event event ) {
      removeRunnable( runnable );
    }
  }

}