Is it possible to start backgroung app when the screen is turned off ? How?

Question

Is it possible to start a background app when a broadcast receiver is activated and the screen is off ? I am not running any service in background just want to wake up and unlock the screen and show an activity from an app that is in the background. At the moment I am able to wake up and unlock the screen only if the app was in foreground when the screen turned off.

Answer 1

After a bit of searching and hair pulling it turns out there are a few things that really matter when one wants to have an activity shown directly above the lockscreen (or better said unlock and show the activity).

When creating a channel (for android 8+) one needs to define the visibility of the channel as: channel.setLockscreenVisibility(Notification.VISIBILITY_PUBLIC); this will show it above the lock screen.

Also the notification needs to have proper visibility like: .setVisibility(NotificationCompat.VISIBILITY_PUBLIC). But to actually start the activity you need to set the fullscreenIntent: builder.setFullScreenIntent(pendingI, true);

If needed and the notification is important and if you need the above then you have very big chances you also need the priotity set: .setVisibility(NotificationCompat.VISIBILITY_PUBLIC).

See the below code examples...

requestCode = 587;
NOTIFICATION_ID = 111;
private void launchFullScreenNotification(Intent activityIntent) {
    PendingIntent pendingI = PendingIntent.getActivity(mContext.getApplicationContext(),
            requestCode, intentTinta, PendingIntent.FLAG_UPDATE_CURRENT);

    NotificationCompat.Builder builder = new NotificationCompat.Builder(mContext, CHANNEL_ID)
            .setLights(Color.WHITE, 2000, 3000)
            .setSound(Settings.System.DEFAULT_NOTIFICATION_URI)
            .setSmallIcon(android.R.drawable.arrow_up_float)
            .setContentTitle("blink blink")
            .setContentText("check me out...")
            // this is important...
            .setPriority(NotificationCompat.PRIORITY_HIGH)
            .setCategory(NotificationCompat.CATEGORY_ALARM)
            // this is important...
            .setVisibility(NotificationCompat.VISIBILITY_PUBLIC)
            .setAutoCancel(true);

    // very important, this is the activity intent to launch automatically
    builder.setFullScreenIntent(pendingI, true);
    Notification incomingCallNotification = builder.build();

    NotificationManagerCompat notifMan = NotificationManagerCompat.from(mContext);
    notifMan.notify(NOTIFICATION_ID, incomingCallNotification);

    PowerManager powerManager = (PowerManager) mContext.getSystemService(POWER_SERVICE);

    if (!powerManager.isInteractive()) { // if screen is not already on, turn it on
        PowerManager.WakeLock wl = powerManager.newWakeLock(PowerManager.FULL_WAKE_LOCK | PowerManager.ACQUIRE_CAUSES_WAKEUP | PowerManager.ON_AFTER_RELEASE, "alarma:SCREENLOCK");
        wl.acquire(60000);
        PowerManager.WakeLock wl_cpu = powerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "alarma:SCREENLOCK");
        wl_cpu.acquire(60000);
    }
}

private void createChannel() {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        mChannel = new NotificationChannel(CHANNEL_ID, channel_name, NotificationManager.IMPORTANCE_HIGH);

        // Configure the notification channel.
        mChannel.setDescription(channel_description);
        mChannel.enableLights(true);
        // Sets the notification light color for notifications posted to this
        // channel, if the device supports this feature.
        mChannel.setLightColor(Color.RED);
        mChannel.enableVibration(true);
        mChannel.setVibrationPattern(new long[]{100, 200, 300, 400, 500, 400, 300, 200, 400});
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
            mChannel.setAllowBubbles(true);
        }
        // this is important...
        mChannel.setLockscreenVisibility(Notification.VISIBILITY_PUBLIC);

        NotificationManager mNotificationManager = (NotificationManager) mContext.getSystemService(NOTIFICATION_SERVICE);
        mNotificationManager.createNotificationChannel(mChannel);
    }
}

Also if you want the activity to be shown above the lockscreen you might be interested in adding either into the manifest something like:

android:turnScreenOn="true"
android:showOnLockScreen="true"

Alternatively you might need to add in the onCreate method after the setContentView() something like:

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O_MR1) {
        this.setTurnScreenOn(true);
        this.setShowWhenLocked(true);
    } else {
        final Window window = getWindow();
        window.addFlags(WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED |
                WindowManager.LayoutParams.FLAG_DISMISS_KEYGUARD |
                WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON |
                WindowManager.LayoutParams.FLAG_TURN_SCREEN_ON |
                WindowManager.LayoutParams.FLAG_ALLOW_LOCK_WHILE_SCREEN_ON);
    }

    KeyguardManager keyguardManager=(KeyguardManager)getSystemService(Context.KEYGUARD_SERVICE) ;
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        keyguardManager.requestDismissKeyguard(this, null);
    }

Since I just discovered how this code works I might discover some other things along the way so bear in mind I might update this answer after some time...