Android：该应用程序可能在其主线程上做了大量工作

Question

I'm trying to load a video thumbnail from url into a grid view. Everything works fine, but I'm getting this message "/Choreographer: Skipped 46 frames! The application may be doing too much work on its main thread."

I know it has something to do with the thumbnail loading in the main thread, but I couldn't find out how to fix this.

I'm also using a device to test.

public class ThumbAdapter  extends ArrayAdapter<Videos> {

    Context context;
    int ressource;
    ThumbAdapter_Holder holder=new ThumbAdapter_Holder();

    public ThumbAdapter(Context context, int resource, ArrayList<Videos> videoList) {
        super(context, resource, videoList);
        this.context=context;
        this.ressource=resource;

    }


    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        View view=convertView;
        if (view==null){

            LayoutInflater inflater = (LayoutInflater) context.getSystemService(context.LAYOUT_INFLATER_SERVICE);
            view = inflater.inflate(ressource,parent,false);

            holder.video_thum = (ImageView) view.findViewById(R.id.video_thum);

            view.setTag(holder);
        }
        else {
            holder=(ThumbAdapter_Holder) view.getTag();
        }

        try {
            holder.video_thum.setImageBitmap(retriveVideoFrameFromVideo(getItem(position).getURL()));
        } catch (Throwable throwable) {
            throwable.printStackTrace();
        }

        return view;
    }


    class ThumbAdapter_Holder{
       ImageView video_thum ;

    }

    public static Bitmap retriveVideoFrameFromVideo(String videoPath) throws Throwable {
        Bitmap bitmap = null;
        MediaMetadataRetriever mediaMetadataRetriever = null;
        try
        {
            mediaMetadataRetriever = new MediaMetadataRetriever();
            if (Build.VERSION.SDK_INT >= 14)
                mediaMetadataRetriever.setDataSource(videoPath, new HashMap<String, String>());
            else
                mediaMetadataRetriever.setDataSource(videoPath);
            //   mediaMetadataRetriever.setDataSource(videoPath);
            bitmap = mediaMetadataRetriever.getFrameAtTime();
        }
        catch (Exception e)
        {
            e.printStackTrace();
            throw new Throwable(
                    "Exception in retriveVideoFrameFromVideo(String videoPath)"
                            + e.getMessage());

        } finally {
            if (mediaMetadataRetriever != null) {
                mediaMetadataRetriever.release();
            }
        }
        return bitmap;
    }
}

Answer 1

The problem is, you are requesting and processing data in each cell of your adapter.

try {
        holder.video_thum.setImageBitmap(retriveVideoFrameFromVideo(getItem(position).getURL()));
    } catch (Throwable throwable) {
        throwable.printStackTrace();
    }

that's the culprit. You are doing an expensive, non graphical task inside the main thread (the one managing the UI). In order to optimize, you need to move that kind of operation to separate threads, and notify a class executing inside the main thread the results so it can update the UI. There are several ways to do this: Asynctasks, Observers, Event buses. For the sake of simplicity, let's go with an asynctask.

take this as an example:

public class BitMapTask extends AsyncTask<Void, Void, Bitmap> {

public interface OnBitmapLoaded{
    void loadBitmap(Bitmap bitmap);
}

private OnBitmapLoaded bitmapLoaded;
private String url;

public BitMapTask(String url){
    this.url = url;
}

public BitMapTask setBitMapLoaded(OnBitmapLoaded bitMapLoaded){
    this.bitmapLoaded = bitMapLoaded;
    return this;
}

@Override
protected Bitmap doInBackground(Void... params) {
    return retriveVideoFrameFromVideo(url);
}

@Override
protected void onPostExecute(Bitmap result){
    if(bitmapLoaded != null) bitmapLoaded.loadBitmap(result);
}
}

then, instead of the try-catch, you should do something like this:

BitMapTask task = new BitMapTask(getItem(position).getURL())
                .setBitMapLoaded(new OnBitmapLoaded() {
            @Override
            public void loadBitmap(Bitmap bitmap) {
                if(bitmap != null){
                    setImageBitmap(bitmap);
                }
            }
        }).executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);

Keep in mind, this kind of operation will ignore the main thread status; that means, the separate threads will keep running and executing even if the app is dormant, therefore, you need to void the listeners/unsubscribe receivers if the app goes to the foreground. Happy coding.