AssetWatcher.java

/**
 * Copyright 2011 The ForPlay Authors
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */
package forplay.core;

/**
 * A utility class that helps keep track of image loading.
 * <p>
 * To use: create a new {@link AssetWatcher}, then add images using
 * {@link AssetWatcher#add(Image)} and finally call {@link AssetWatcher#start()}.
 */
public class AssetWatcher {
  /**
   * Listener interface for AssetWatcher.
   */
  public interface Listener {
    /**
     * Called when all assets are done loading (or had an error).
     */
    void done();

    /**
     * Called for each asset that failed to load.
     */
    void error(Throwable e);
  }

  private int total, loaded, errors;
  private boolean start;
  private final Listener listener;

  @SuppressWarnings("rawtypes")
  private ResourceCallback callback = new ResourceCallback() {
    @Override
    public void done(Object resource) {
      ++loaded;
      maybeDone();
    }

    @Override
    public void error(Throwable e) {
      ++errors;
      if (listener != null)
        listener.error(e);
      maybeDone();
    }
  };

  /**
   * Creates a new watcher without a listener.
   */
  public AssetWatcher() {
    this(null);
    start();
  }

  /**
   * Creates a new watcher with the given listener.
   * <p>
   * Note: must call {@link AssetWatcher#start()} after adding your resources.
   */
  public AssetWatcher(Listener listener) {
    this.listener = listener;
  }

  /**
   * Adds an image resource to be watched.
   */
  @SuppressWarnings("unchecked")
  public void add(Image image) {
    Asserts.checkState(!start || listener == null);
    ++total;
    image.addCallback(callback);
  }

  /**
   * Whether all resources have completed loading, either successfully or in error.
   */
  public boolean isDone() {
    return start && (loaded + errors == total);
  }

  /**
   * Done adding resources; {@link Listener#done()} will be called as soon as all assets are done
   * being loaded.
   * 
   * There is no need to call this method if there is no listener. {@link #isDone()} will return
   * <code>true</code> as soon as all pending assets are loaded.
   */
  public void start() {
    start = true;
    maybeDone();
  }

  private void maybeDone() {
    if (isDone()) {
      if (listener != null) {
        listener.done();
      }
    }
  }
}