Android Galaxy S4 -- Activity that is visible over lock screen

Not sure if this is the problem in all cases, but the documentation on ShowWhenLocked says it applies only to the top-most full-screen window. I had a window themed as a dialog which was not working, but it worked fine once I changed it to a regular full-screen window.

I figured it out, and the answer was very different from what I expected.

This piece of code was included in the alarm clock sample from Android 2, in the AlarmAlert.java Activity:

@Override
protected void onStop() {
    super.onStop();
    // Don't hang around.
    finish();
}

For reference, you can see the file from the example code in Git's past right here, containing the above onStop function. It never caused a problem in Android 2.

But in Android 4, if the phone was off, this onStop would fire right before the phone woke up, effectively "minimizing" the Activity. Once I removed this function, it immediately worked again.

But I wonder, is this the problem that other people like @radley and @Guardanis are getting? It seems unlikely, but please let me know if this fixes your problems too.

If you're visiting this answer in the future, and you're getting this problem, what I would try is:

1. Take out any onStop functions.

2. Add this code to the Activity:

   getWindow().addFlags(WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED
           | WindowManager.LayoutParams.FLAG_DISMISS_KEYGUARD
           | WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON
           | WindowManager.LayoutParams.FLAG_TURN_SCREEN_ON);
   

3. Make sure you're using a full screen theme, and not a dialog theme.

4. This didn't make a difference for me, but you could try setting showOnLockScreen explicitly in the manifest: <activity android:name="com.example.MyActivity" android:showOnLockScreen="true"/>

5. A second thing that didn't make a difference for me but you might try is adding the flag WindowManager.LayoutParams.FLAG_FULLSCREEN

I hope this helps other people!

In Kotlin,

For Api level 28 or less, you can simply add below method in your activity that needs to be opened:

override fun onAttachedToWindow() {
    super.onAttachedToWindow()
    toBeShownOnLockScreen()
}

private fun toBeShownOnLockScreen() {
    window.addFlags(
        WindowManager.LayoutParams.FLAG_DISMISS_KEYGUARD
                or WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON
    )
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O_MR1) {
        setTurnScreenOn(true)
        setShowWhenLocked(true)
    } else {
        window.addFlags(
            WindowManager.LayoutParams.FLAG_TURN_SCREEN_ON
                    or WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED
        )
    }
}

And to make it work on Android Pie and above, in additional to above step, we need to set in AndroidManifest as well:

<activity
    android:name=".view.activity.LockScreenActivity"
    android:showOnLockScreen="true"
    android:showWhenLocked="true"
    android:turnScreenOn="true" />

I have tested this code from Api level 21 to 29, and works like charm!