Mulgard Mulgard - 6 months ago 122
Android Question

Updating ProgressBar from AsyncTask lagging UI

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

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;
        }

    }
}
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