我使用此示例中的 ListAdapter:
http://code.google.com/p/au-optimizing-layouts-201/source/browse/au_optimizinglayouts/src/com/example/android/training/optimizinglayouts/OptimizedListAdapter.java?r=4 http://code.google.com/p/au-optimizing-layouts-201/source/browse/au_optimizinglayouts/src/com/example/android/training/optimizinglayouts/OptimizedListAdapter.java?r=4
这个例子不是很好,因为列表中的元素根据我滚动的速度被绘制了几次。那是因为只重用了一个
private FakeImageLoader mFakeImageLoader;
如果 FakeImageLoader.java getImage() 将加载真实图像。
需要做什么才能让这个示例运行并保持性能?
public class OptimizedListAdapter extends BaseAdapter{
...
private FakeImageLoader mFakeImageLoader;
public OptimizedListAdapter(Context cxt)
{
// Cache the LayoutInflate to avoid asking for a new one each time.
mLayoutInflater = LayoutInflater.from(cxt);
mFakeImageLoader = new FakeImageLoader(cxt);
...
public View getView(final int position, View convertView, ViewGroup parent)
{
// A ViewHolder keeps references to children views to avoid unneccessary calls
// to findViewById() on each row.
ViewHolder holder;
// When convertView is not null, we can reuse it directly, there is no need
// to reinflate it. We only inflate a new View when the convertView supplied
// by ListView is null.
if(convertView==null)
{
convertView = mLayoutInflater.inflate(R.layout.listitem, null);
// Creates a ViewHolder and store references to the two children views
// we want to bind data to.
holder = new ViewHolder();
holder.icon = (ImageView) convertView.findViewById(R.id.listitem_image);
holder.text = (TextView) convertView.findViewById(R.id.listitem_text);
holder.timestamp = (TextView) convertView.findViewById(R.id.listitem_timestamp);
convertView.setTag(holder);
}else
{
holder = (ViewHolder) convertView.getTag();
}
//holder.icon.setImageDrawable(drawable);
holder.text.setText(new StringBuffer(ITEM_PRE_TEXT).append(position));
holder.timestamp.setText(""+(System.currentTimeMillis()-START_TIMESTAMP));
holder.position = position;
//during a fast scroll this could start 100's of threads, need a thread pool processing them!
//see previous ImageLoader.
new AsyncTask<ViewHolder, Void, Bitmap>() {
private ViewHolder v;
@Override
protected Bitmap doInBackground(ViewHolder... params) {
v = params[0];
return mFakeImageLoader.getImage();
}
@Override
protected void onPostExecute(Bitmap result) {
super.onPostExecute(result);
if(v.position == position)
{
v.icon.setImageBitmap(result);
}
}
}.execute(holder);
//holder.icon.setImageBitmap(mFakeImageLoader.getImage());
return convertView;
}
谢谢塔塔
我用过这个通用图像加载库 https://github.com/nostra13/Android-Universal-Image-Loader通用图像加载器库在一个应用程序中下载图像,它对我来说更有用。
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