Updating ProgressBar from AsyncTask lagging UI

Question

I have a Fragment with a RecyclerView and the RecyclerView's ViewHolder is holding a ProgressBar to show the progress of a downloading process.

public static class ViewHolder extends RecyclerView.ViewHolder {
    ....
    private ProgressBar progressBar = null;
    ....
    public ViewHolder(View itemView) {
        super(itemView);

        ....
        this.progressBar = (ProgressBar) itemView.findViewById(R.id.progessbar);
        ....
    }
}

I created a callback for my Fragment:

public interface CallbackItemChanged {
    void onItemChanged(final int position);
}

And if it is called i do:

@Override
public void onItemChanged(final int position) {
    this.adapter.notifyItemChanged(position);
}

And in my AsyncTask:

protected void onProgressUpdate(Integer... progress) {
    super.onProgressUpdate(progress);

    this.entry.setProgress(progress[0]);
    this.entry.setProgressString(progress[0] + "%");

    this.callbackItemChanged.onItemChanged(this.entry.getPosition());
}

The progress is published successfully but the ui is lagging like hell but i dont know why? The onProgressUpdate is running on the ui thread isnt it? I think it should be like that or am i wrong?

How can i get the ui smoothly working while updating the progressbar?

EDIT

@Override
protected String doInBackground(Void... params) {
    this.inputStream = null;
    this.outputStream = null;
    this.connection = null;

    File file = new File(this.entry.getPath(this.context));
    File parent = file.getParentFile();

    try {
        parent.mkdirs();
        file.createNewFile();

        this.connection = (HttpsURLConnection) new URL(this.entry.getUrl()).openConnection();
        this.connection.connect();

        int fileLength = this.connection.getContentLength();

        this.inputStream = this.connection.getInputStream();
        this.outputStream = new FileOutputStream(file);

        byte data[] = new byte[4096];
        long progress = 0;
        int count;

        while ((count = this.inputStream.read(data)) != -1) {
            if (this.isCancelled() || this.entry.isCancelled()) {
                this.handleClose();
                this.handleDelete();

                return null;
            }

            if (fileLength > 0) {
                this.publishProgress((int) ((progress +=count) * 100 / fileLength));
            }

            this.outputStream.write(data, 0, count);
        }
    } catch (Exception e) {
        this.handleDelete();

        return e.toString();
    } finally {
        this.handleClose();
    }

    return null;
}

Answer 1

You're publishing the progress inside a loop, so your main thread will be called a lot of times.

You could delay the progress publishing with a simple Thread.sleep():

    while ((count = this.inputStream.read(data)) != -1) {
        if (this.isCancelled() || this.entry.isCancelled()) {
            this.handleClose();
            this.handleDelete();

            return null;
        }

        // Write the data before publishing the progress
        this.outputStream.write(data, 0, count);

        try{
            // Adjust this value. It shouldn't be too small.
            Thread.sleep(100);
        }catch (InterruptedException e){
            // Nothing you can do here
        }finally {
            if (fileLength > 0) {
                this.publishProgress((int) ((progress +=count) * 100 / fileLength));
            }
        }
    }

Or you could publish only by increments of x%:

while ((count = this.inputStream.read(data)) != -1) {
    if (this.isCancelled() || this.entry.isCancelled()) {
        this.handleClose();
        this.handleDelete();

        return null;
    }

    // Write the data before publishing the progress
    this.outputStream.write(data, 0, count);

    if (fileLength > 0) {
        currentProgress = ((progress += count) * 100 / fileLength);
        // Publish only on increments of 1%
        if (currentProgress >= previousProgress + 1) {
            this.publishProgress(currentProgress);
            previousProgress = currentProgress;
        }

    }
}