Android ListView只加载当前屏幕内的图片（解决list滑动时加载卡顿）

最近在做ListView分页显示，其中包括图片 和文字（先下载解析文字内容，再异步加载图片）发现每次点击下一页后，文字内容加载完毕，马上向下滑动，由于这时后台在用线程池异步下载图片，我每页有20条，也就是20张图片，会导致listview滑动卡顿！

这是用户不想看到的，我参考了网易新闻和电子市场等应用，发现它们都是只加载屏幕内的图片，不现实的不加载,于是我也仿照做了一个。我是菜鸟，我承认 呵呵，虽然不见得完全和他们的一样，但是确实解决了翻页时那一刻的卡顿现象。

因为未发现网上有相关文章，希望对朋友们有用~

下面是相关代码（分页的就没放）：

/**
* list滚动监听
*/
listView.setOnScrollListener(new OnScrollListener() {
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
// TODO Auto-generated method stub
// 异步加载图片
if (scrollState == OnScrollListener.SCROLL_STATE_IDLE) {//list停止滚动时加载图片
pageImgLoad(_start_index, _end_index);
}
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount,  int totalItemCount) {
// TODO Auto-generated method stub
//设置当前屏幕显示的起始index和结束index
_start_index = firstVisibleItem;
_end_index = firstVisibleItem + visibleItemCount;
if (_end_index >= totalItemCount) {
_end_index = totalItemCount - 1;
}
}
});

	/**
		 * list滚动监听
		 */
		listView.setOnScrollListener(new OnScrollListener() {
			@Override
			public void onScrollStateChanged(AbsListView view, int scrollState) {
				// TODO Auto-generated method stub
				// 异步加载图片
				if (scrollState == OnScrollListener.SCROLL_STATE_IDLE) {//list停止滚动时加载图片
					pageImgLoad(_start_index, _end_index);
				}
			}
			@Override
			public void onScroll(AbsListView view, int firstVisibleItem,
					int visibleItemCount, int totalItemCount) {
				// TODO Auto-generated method stub
				//设置当前屏幕显示的起始index和结束index
				_start_index = firstVisibleItem;
				_end_index = firstVisibleItem + visibleItemCount;
				if (_end_index >= totalItemCount) {
					_end_index = totalItemCount - 1;
				}
			}
		});

/**
* 只加载from start_index to end_index 的图片
* @param start_index
* @param end_index
*/
private void pageImgLoad(int start_index, int end_index) {
for (; start_index < end_index; start_index++) {
HashMap<String, Object> curr_item = adapter.getItem(start_index);
if (curr_item.get(Constant.NEWS_ICON_URL) != null
&& curr_item.get(Constant.NEWS_ICON) == null) {
loadImage(curr_item);
}
}
}

/**
	 * 只加载from start_index to end_index 的图片 
	 * @param start_index
	 * @param end_index
	 */
	private void pageImgLoad(int start_index, int end_index) {
		for (; start_index < end_index; start_index++) {
			HashMap<String, Object> curr_item = adapter.getItem(start_index);
			if (curr_item.get(Constant.NEWS_ICON_URL) != null
					&& curr_item.get(Constant.NEWS_ICON) == null) {
				loadImage(curr_item);
			}
		}
	}

异步加载图片代码，这里我之前使用的是AsyncTask，但是继承AsyncTask后不能被执行多次，所以我改用了线程呼叫handler更新UI：

/**
* 异步加载图片
* @param curr_item
*/
private void loadImage(final HashMap<String, Object> curr_item) {
executorService.submit(new Runnable() {
public void run() {
try {
Drawable curr_icon = null;
String icon_URL = (String) curr_item
.get(Constant.NEWS_ICON_URL);
String newsId = (String) curr_item.get(Constant.NEWS_ID);

if (imageCache.containsKey(icon_URL)) {//软引用
SoftReference<Drawable> softReference = imageCache
.get(icon_URL);
curr_icon = softReference.get();
System.out.println("CASE USING SoftReference!!!!!!!!!!!!!!!!!!!!");
}
if (curr_icon == null) {
HttpUtils hu = new HttpUtils();
FileUtils fu = new FileUtils();
if (hu.is_Intent(Home_Activity.this)) {
fu.write2LocalFromIS(Home_Activity.this, newsId
+ Constant.SAVE_NEWS_ICON_NAME
+ Constant.SAVE_IMG_SUFFIX,
hu.getISFromURL(icon_URL));
}
// 从本地加载图片 如果没网则直接加载本地图片
curr_icon = fu.readDrawableFromLocal(
Home_Activity.this, newsId
+ Constant.SAVE_NEWS_ICON_NAME
+ Constant.SAVE_IMG_SUFFIX);
imageCache.put(icon_URL, new SoftReference<Drawable>(
curr_icon));
}
curr_item.put(Constant.NEWS_ICON, curr_icon);
// UI交给handler更新
Message msg = _viewHandler.obtainMessage();
msg.arg1 = Constant.MSG_LIST_IMG_OK;
msg.sendToTarget();
} catch (Exception e) {
throw new RuntimeException(e);
}
}
});
}

/**
	 * 异步加载图片
	 * @param curr_item
	 */
	private void loadImage(final HashMap<String, Object> curr_item) {
		executorService.submit(new Runnable() {
			public void run() {
				try {
					Drawable curr_icon = null;
					String icon_URL = (String) curr_item
							.get(Constant.NEWS_ICON_URL);
					String newsId = (String) curr_item.get(Constant.NEWS_ID);

					if (imageCache.containsKey(icon_URL)) {//软引用
						SoftReference<Drawable> softReference = imageCache
								.get(icon_URL);
						curr_icon = softReference.get();
						System.out.println("CASE USING SoftReference!!!!!!!!!!!!!!!!!!!!");
					}
					if (curr_icon == null) {
						HttpUtils hu = new HttpUtils();
						FileUtils fu = new FileUtils();
						if (hu.is_Intent(Home_Activity.this)) {
							fu.write2LocalFromIS(Home_Activity.this, newsId
									+ Constant.SAVE_NEWS_ICON_NAME
									+ Constant.SAVE_IMG_SUFFIX,
									hu.getISFromURL(icon_URL));
						}
						// 从本地加载图片 如果没网则直接加载本地图片
						curr_icon = fu.readDrawableFromLocal(
								Home_Activity.this, newsId
										+ Constant.SAVE_NEWS_ICON_NAME
										+ Constant.SAVE_IMG_SUFFIX);
						imageCache.put(icon_URL, new SoftReference<Drawable>(
								curr_icon));
					}
					curr_item.put(Constant.NEWS_ICON, curr_icon);
					// UI交给handler更新
					Message msg = _viewHandler.obtainMessage();
					msg.arg1 = Constant.MSG_LIST_IMG_OK;
					msg.sendToTarget();
				} catch (Exception e) {
					throw new RuntimeException(e);
				}
			}
		});
	}

handler代码：

handler代码：

Handler _viewHandler = new Handler() {

Handler _viewHandler = new Handler() {

@Override
public void handleMessage(Message msg) {
switch (msg.arg1) {
case Constant.MSG_LIST_IMG_OK:
// 更新UI
adapter.notifyDataSetChanged();
break;
}
super.handleMessage(msg);
}
};

	@Override
		public void handleMessage(Message msg) {
			switch (msg.arg1) {
			case Constant.MSG_LIST_IMG_OK:
				// 更新UI
				adapter.notifyDataSetChanged();
				break;
			}
			super.handleMessage(msg);
		}
	};

上个图吧：