Android Open Source - Android-Universal-Image-Loader Pause On Scroll Listener

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License

The source code is released under:

Apache License

Java Source Code

/*******************************************************************************
 * Copyright 2011-2013 Sergey Tarasevich
 */*from   w w w .  ja  v  a 2s  . co m*/
 * 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 com.nostra13.universalimageloader.core.listener;

import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.GridView;
import android.widget.ListView;
import com.nostra13.universalimageloader.core.ImageLoader;

/**
 * Listener-helper for {@linkplain AbsListView list views} ({@link ListView}, {@link GridView}) which can
 * {@linkplain ImageLoader#pause() pause ImageLoader's tasks} while list view is scrolling (touch scrolling and/or
 * fling). It prevents redundant loadings.<br />
 * Set it to your list view's {@link AbsListView#setOnScrollListener(OnScrollListener) setOnScrollListener(...)}.<br />
 * This listener can wrap your custom {@linkplain OnScrollListener listener}.
 *
 * @author Sergey Tarasevich (nostra13[at]gmail[dot]com)
 * @since 1.7.0
 */
public class PauseOnScrollListener implements OnScrollListener {

  private ImageLoader imageLoader;

  private final boolean pauseOnScroll;
  private final boolean pauseOnFling;
  private final OnScrollListener externalListener;

  /**
   * Constructor
   *
   * @param imageLoader   {@linkplain ImageLoader} instance for controlling
   * @param pauseOnScroll Whether {@linkplain ImageLoader#pause() pause ImageLoader} during touch scrolling
   * @param pauseOnFling  Whether {@linkplain ImageLoader#pause() pause ImageLoader} during fling
   */
  public PauseOnScrollListener(ImageLoader imageLoader, boolean pauseOnScroll, boolean pauseOnFling) {
    this(imageLoader, pauseOnScroll, pauseOnFling, null);
  }

  /**
   * Constructor
   *
   * @param imageLoader    {@linkplain ImageLoader} instance for controlling
   * @param pauseOnScroll  Whether {@linkplain ImageLoader#pause() pause ImageLoader} during touch scrolling
   * @param pauseOnFling   Whether {@linkplain ImageLoader#pause() pause ImageLoader} during fling
   * @param customListener Your custom {@link OnScrollListener} for {@linkplain AbsListView list view} which also
   *                       will be get scroll events
   */
  public PauseOnScrollListener(ImageLoader imageLoader, boolean pauseOnScroll, boolean pauseOnFling,
      OnScrollListener customListener) {
    this.imageLoader = imageLoader;
    this.pauseOnScroll = pauseOnScroll;
    this.pauseOnFling = pauseOnFling;
    externalListener = customListener;
  }

  @Override
  public void onScrollStateChanged(AbsListView view, int scrollState) {
    switch (scrollState) {
      case OnScrollListener.SCROLL_STATE_IDLE:
        imageLoader.resume();
        break;
      case OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:
        if (pauseOnScroll) {
          imageLoader.pause();
        }
        break;
      case OnScrollListener.SCROLL_STATE_FLING:
        if (pauseOnFling) {
          imageLoader.pause();
        }
        break;
    }
    if (externalListener != null) {
      externalListener.onScrollStateChanged(view, scrollState);
    }
  }

  @Override
  public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
    if (externalListener != null) {
      externalListener.onScroll(view, firstVisibleItem, visibleItemCount, totalItemCount);
    }
  }
}

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