Android application doing too much work on main thread

Question

I call function processImage() on a button click and could't get the exact output needed.

processImage() function,

private void processImage() {
    TextRecognizer textRecognizer = new TextRecognizer.Builder(getApplicationContext()).build();
    if (textRecognizer.isOperational()) {
        Log.d("IMAGE-PROCESS", "started");

        Frame frame = new Frame.Builder().setBitmap(bitmap).build();
        final SparseArray<TextBlock> items = textRecognizer.detect(frame);

        runOnUiThread(new Runnable(){
            public void run() {
                StringBuilder stringBuilder = new StringBuilder();
                for (int i = 0; i < items.size(); i++) {
                    TextBlock textBlock = items.valueAt(i);
                    stringBuilder.append(textBlock.getValue());
                    stringBuilder.append("\n");
                }
                try {
                    Log.d("IMAGE-PROCESS", "finished");
                    Log.d("OUTPUT", stringBuilder.toString());
                    textView.setText(stringBuilder.toString());
                } catch (final Exception ex) {
                    Log.i("EXC","Exception in thread");
                }
            }
        });
    } else {
        Log.d("IMAGE-PROCESS", "not operational");
    }
}

It logs

I/Choreographer: Skipped 86 frames! The application may be doing too much work on its main thread.

Do I need to change anything in my function? Help me to fix this

maybe duplicated of : https://stackoverflow.com/questions/14678593/the-application-may-be-doing-too-much-work-on-its-main-thread — SAYE, Apr 24 '18 at 14:39

score 2 · Accepted Answer · answered Apr 24 '18 at 14:48

You need to make sure that the processImage method runs on a background (non-ui) thread. It is probably running on the UI thread now, and you get the warning because it is blocking the UI thread.

There are a number of ways to do work on a background thread, from simply spawning a new thread to creating a service - you will need to research this, and decide on the best method for your particular situation. Just remember that when your background processing is complete, you need to transfer the data to the UI thread, and update the UI from the UI thread, as attempting an update from another thread will cause a crash.

My only specific advice is to not use an AsyncTask. They sound great in theory, but unless you really know how they work, they can get you into a lot of trouble. And if you really know how they work, you're fully capable of doing something more reliable.

score 0 · Answer 2 · answered Apr 24 '18 at 15:42

Where is the posted code located?

Usually, even if the hard work is done on the UI thread, the screen will freeze/stutter, but eventually, the desired output is produced. I'd guess 86 skipped frames is ~1.25 s of freezing.

If your processImage() method is inside a Runnable, Callable<>, or the like, then one could understand the use of Activity.runOnUiThread(), but..
Since you are getting this message, and you did not mention this imporant detail, I'll assume that your code runs on the UI thread.

Image processing is an expensive task, and should be carried out on a background thread.

To do an kind of background work, you should use some of the ready-made classes (e.g. AsyncTask, Service, etc.), or create ones on your own (with the help of Executors or the like).

Find out how to do that here

Android application doing too much work on main thread

2 Answers2