PARTIAL_WAKE_LOCK does not work

Question

I created a new project with target API 15 (ICS) with empty Activity. I added permission to manifest:

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

I added code to onCreate():

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        PowerManager pm = (PowerManager) getSystemService(getApplicationContext().POWER_SERVICE);
        PowerManager.WakeLock wl = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "Tag");
        wl.acquire();

        WindowManager.LayoutParams params = getWindow().getAttributes();
        params.flags |= WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON;
        params.screenBrightness = 0;
        getWindow().setAttributes(params);
    }

But nothing happens with the device. According to PowerManager documentation I expected the screen to go off (immediately). So, am I doing something wrong or is this not working?

EDIT:

I tried Ashish Ranjan's suggestion to manually set screenBrightness after acquiring WakeLock but this too does not work.

are you expecting that this will turn off the display, instantaneously? — Ashish Ranjan, Jul 15 '16 at 13:35

score 1 · Answer 1 · edited Jun 20 '20 at 09:12

1

As per the Android documentation, using PARTIAL_WAKE_LOCK won't turn the screen off. But it will allow the screen to go off, when this mode is active in the WakeLock.

So, the device screen won't turn off instantly, you'll have to wait for the screen to timeout (which depends on the time set in the device display settings) but the CPU will keep running.

PARTIAL_WAKE_LOCK

Wake lock level: Ensures that the CPU is running; the screen and keyboard backlight will be allowed to go off.

If the user presses the power button, then the screen will be turned off but the CPU will be kept on until all partial wake locks have been released.

To turn off the screen you'll have to change the Window LayoutParams like this :

WindowManager.LayoutParams params = getWindow().getAttributes();
params.flags |= LayoutParams.FLAG_KEEP_SCREEN_ON;
params.screenBrightness = 0;
getWindow().setAttributes(params);

edited Jun 20 '20 at 09:12

Community

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answered Jul 15 '16 at 13:41

Ashish Ranjan

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Alright, thanks for missing info. I read about manually setting attributes but the problem is that I want to do this from Service where no GUI is available (thus `getWindow` won't work). Will search further. – c0dehunter Jul 15 '16 at 13:49
you can do it from a service as well (ofcourse using a different method) but why do you wanna turn off the screen? It isn't a good idea to do so generally. – Ashish Ranjan Jul 15 '16 at 13:53
I know I can but I need to create a dummy activity in which I do this stuff [see this answer](http://stackoverflow.com/a/11306685/1181261). I have a special use case for my client and I need to do this. – c0dehunter Jul 15 '16 at 13:55
yes exactly using a dummy activity, oh okay good luck with the implementation! – Ashish Ranjan Jul 15 '16 at 13:58
Thanks;) However, concerning screen off, it still doesn't work (see edit). – c0dehunter Jul 15 '16 at 14:01
oh let me check it on my device. I've used this, it used to work. – Ashish Ranjan Jul 15 '16 at 14:02
yeah not completely turning off, just dims the screen. – Ashish Ranjan Jul 15 '16 at 14:06
Yeah.. I need to turn the screen of completely. – c0dehunter Jul 15 '16 at 14:10

score 0 · Answer 2 · answered Jul 15 '16 at 13:23

0

I think you forgot to add this :

 wl.release();

answered Jul 15 '16 at 13:23

Lubomir Babev

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Added this line to be executed in `onPause()`. Did not help (as I expected). – c0dehunter Jul 15 '16 at 13:27
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this is to release wake lock, not to turn it on and is used when you're done with the wake lock. From the docs : *This method releases your claim to the CPU or screen being on. The screen may turn off shortly after you release the wake lock, or it may not if there are other wake locks still held.* https://developer.android.com/reference/android/os/PowerManager.WakeLock.html#release() – Ashish Ranjan Jul 15 '16 at 13:28
But I'm trying to turn off the screen with `acquire()` (and keep CPU on). – c0dehunter Jul 15 '16 at 13:33

PARTIAL_WAKE_LOCK does not work

2 Answers2