Android Black Screen after Unlocking

Issue

I'm having trouble with resuming an app's activity after locking the device screen.

Here's the typical situation:

1. App is running.
2. Lock device.
3. Unlock device.
4. Instead of returning to running app, it shows a black screen.

I checked how the activity lifecycle is running and it seems this is what's happening when it unlocks:

1. Create
2. Start
3. Resume
4. Pause

Why is it stuck on pause? I'm sure this is really simple but as I'm still learning Android I'm super confused. Thanks for any help given!

---

EDIT:

I don't think I'm doing anything out of the ordinary but here's the basic code I'm using...

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    Log.i("Java", "Create");

    // Initialize NDK audio properties here

    // Initialize the Content View
    setContentView(R.layout.activity_main);

    // Setup toolbar
    Toolbar myToolbar = (Toolbar) findViewById(R.id.toolBar);
    setSupportActionBar(myToolbar);

    // Start thread
    thread = new Thread() {
        public void run() {
            setPriority(Thread.MAX_PRIORITY);
            // Audio Thread is running here
        }
    };
    thread.start();
}

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
}

@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
    super.onRestoreInstanceState(savedInstanceState);
}

@Override
protected void onStart() {
    super.onStart();
}

@Override
protected void onPause() {
    super.onPause();
    if (thread != null) {
        try {
            thread.join();
        }
        catch (InterruptedException e) {
            // e.printStackTrace();
        }
        thread = null;
    }
}

@Override
protected void onResume() {
    super.onResume();
}

@Override
protected void onStop() {
    super.onStop();
}

Solution

I am not thread expert. but here it seems you are blocking ui thread in onpause. thread.join causes the current thread(in this case ui thread) to pause execution until thread terminates.

Answered By - Vivart