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：

转自：http://blog.csdn.net/fengkuanghun/article/details/6922131