PauseOnScrollListener.java

/*******************************************************************************
 * Copyright 2011-2013 Sergey Tarasevich
 *
 * 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.assist;

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);
		}
	}
}