Android Training - 提升布局文件的性能(Lesson 4 - 使用ViewHolder来提升ListView的性能)

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

// Using an AsyncTask to load the slow images in a background thread
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) {
// If this item hasn't been recycled already, hide the
// progress and set and show the image
v.progress.setVisibility(View.GONE);
v.icon.setVisibility(View.VISIBLE);
v.icon.setImageBitmap(result);
}
}
}.execute(holder);

1
2
3
4
5
6
7

static class ViewHolder {
TextView text;
TextView timestamp;
ImageView icon;
ProgressBar progress;
int position;
}

1
2
3
4
5
6

ViewHolder 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);
holder.progress = (ProgressBar) convertView.findViewById(R.id.progress_spinner);
convertView.setTag(holder);