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）：

Java代码







/**

* 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;

}

}

});

[java] view plaincopy

/**

* 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;

}

}

});

Java代码







/**

* 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);

}

}

}

[java] view plaincopy

/**

* 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：

Java代码







/**

* 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);

}

}

});

}

[java] view plaincopy

/**

* 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);

}

}

});

}

Java代码







handler代码：

[java] view plaincopy

handler代码：

Java代码







Handler _viewHandler = new Handler() {

[java] view plaincopy

Handler _viewHandler = new Handler() {

Java代码







@Override

public void handleMessage(Message msg) {

switch (msg.arg1) {

case Constant.MSG_LIST_IMG_OK:

// 更新UI

adapter.notifyDataSetChanged();

break;

}

super.handleMessage(msg);

}

};

[java] view plaincopy

@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