在instantiateItem (PagerAdapter)中使用AsyncTask不能提高性能

Question

我使用ViewPager全屏显示我的图像。基本上你点击图片缩略图，一个新的活动开始，它全屏显示图片。从系统的文件路径中创建位图显示图像。由于位图处理是资源密集型的，我将其移动到AsyncTask线程中。然而，尽管这样做了，我还是没有看到性能的提高。

我的活动转换仍然延迟，我没有看到任何进展对话框。

public class ZoomImageAdapter extends PagerAdapter {
private Context mContext;
private List<String> imagePathData = new ArrayList<String>();
private LayoutInflater layoutInflater;
private View itemView;
private TouchImageView imageView;
private ViewGroup container;

public ZoomImageAdapter(Context context, List<String> data){
    this.mContext = context;
    this.imagePathData = data;
}
@Override
public int getCount() {
    return this.imagePathData.size();
}
@Override
public boolean isViewFromObject(View view, Object object) {
    return view == ((RelativeLayout) object);
}
@Override
public Object instantiateItem(ViewGroup container, int position) {
    this.container = container;      
    BitmapHandling bitmapHandling = new BitmapHandling();
    bitmapHandling.execute(imagePathData.get(position));
    View result = null;
    try {
        result = bitmapHandling.get();
    } catch (InterruptedException e) {
        e.printStackTrace();
    } catch (ExecutionException e) {
        e.printStackTrace();
    }
    return result;
}
private class BitmapHandling extends AsyncTask<String, View, View>{
    ProgressDialog progressDialog;
    String path;
    Bitmap bitmap;
    @Override
    protected void onPreExecute(){
        progressDialog = ProgressDialog.show(mContext,"","");
        layoutInflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        itemView = layoutInflater.inflate(R.layout.item_zoomimage, container, false);
    }
    @Override
    protected View doInBackground(String... params) {
        path = params[0];
        bitmap = Utility.compressBitmap(BitmapFactory.decodeFile(path), 720);
        return itemView;
    }
    @Override
    protected void onPostExecute(View result){
        progressDialog.dismiss();
        imageView = (TouchImageView) result.findViewById(R.id.iv_zoomImage);
        imageView.setImageBitmap(bitmap);
        ((ViewPager) container).addView(result, 0);
    }
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
    ((ViewPager) container).removeView((RelativeLayout) object);
}
}

Answer 1

你的代码甚至不会编译，只是看看doInBackground()方法:)

无论如何-它不工作，因为你调用AsyncTask.get()这是阻塞。它等待后台任务完成并返回其结果。

你必须立即从你的instantiateItem()方法返回一些东西(可能是自定义视图)，并从那里开始BitmapHandling任务。