Question

I plan to do background service which will make screen flashing/blinking until user touches screen.

I do not know methods how to make screen flashing – only what learned that could be done with brightness and control via spawned activity.

Want to do flashing with color change on screen i.e. black and white or screen on/off to make it more visible than wih brightness.

Answer 1

From your Service you can interact with the WakeLock:

Acquire the WakeLock with:

PowerManager powerMan = (PowerManager) getSystemService(Context.POWER_SERVICE);
PowerManager.WakeLock wakeLock = powerMan.newWakeLock(
                     PowerManager.SCREEN_DIM_WAKE_LOCK | 
                     PowerManager.ACQUIRE_CAUSES_WAKEUP, "wakelockTag");

Then to turn the screen on:

wakeLock.acquire();

Then to turn it off again:

wakeLock.release(); 

And you could put this into a Thread with a sleep or use a Timer to create the flash.

For example:

new Thread() {
            public void run() {
                boolean screenOn = false;
                for (int i = 0; i < 5; i++) {
                    try {
                        sleep(500);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    if (screenOn) {
                        wakeLock.acquire();
                    } else {
                        wakeLock.release();
                    }
                }
            }
        }.run();

It wouldn’t be black/white, just on/off.

If you wanted to go black/white you would have to also disengage the KeyLock (Look up the Android Keyguard), and then push an Activity that was completely Black, then change the Activity to White on a Timer or in a Thread as before. Much more work.

Remember to get permission in the AndroidManifest.xml:

<uses-permission android:name="android.permission.WAKE_LOCK" />

Additional permissions will be required for unlocking the KeyGuard if you go down that route.