How to keep the screen on in Qt for android?

Question

I found a couple of solutions how to do that in Java, but did not find how can I do it in QML or Qt. I know that first I should set the WAKE_LOCK permission in AndroidManifest.xml. What should I do to make it possible to turn on and off the screen locking from Qt in runtime?

score 13 · Answer 1 · answered Aug 09 '16 at 09:08

Use window.callMethod<void> instead of window.callObjectMethod
Run on GUI thread with QtAndroid::runOnAndroidThread
Clear exceptions afterwards
To disable always on behaviour, use clearFlags

This is tested Qt 5.7 code:

void keep_screen_on(bool on) {
  QtAndroid::runOnAndroidThread([on]{
    QAndroidJniObject activity = QtAndroid::androidActivity();
    if (activity.isValid()) {
      QAndroidJniObject window =
          activity.callObjectMethod("getWindow", "()Landroid/view/Window;");

      if (window.isValid()) {
        const int FLAG_KEEP_SCREEN_ON = 128;
        if (on) {
          window.callMethod<void>("addFlags", "(I)V", FLAG_KEEP_SCREEN_ON);
        } else {
          window.callMethod<void>("clearFlags", "(I)V", FLAG_KEEP_SCREEN_ON);
        }
      }
    }
    QAndroidJniEnvironment env;
    if (env->ExceptionCheck()) {
      env->ExceptionClear();
    }
  });
}

score 9 · Accepted Answer · answered Jan 04 '15 at 06:33

9

You can use the Qt Android Extras module and use JNI to call the relevant Java function from C++. Something like :

void keepScreenOn() 
{
    QAndroidJniObject activity = QtAndroid::androidActivity();
    if (activity.isValid()) {
        QAndroidJniObject window = activity.callObjectMethod("getWindow", "()Landroid/view/Window;");

        if (window.isValid()) {
            const int FLAG_KEEP_SCREEN_ON = 128;
            window.callObjectMethod("addFlags", "(I)V", FLAG_KEEP_SCREEN_ON);
        }
    }
}

answered Jan 04 '15 at 06:33

Nejat

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If I call it in main() it is working as expected, but if I call it in a slot it is not working and throwing some java exception. Is the QGuiApplication event loop moving to different thread after calling exec(). – Uga Buga Feb 22 '15 at 23:09
No. `QGuiApplication` would remain in the application main thread. May be it is better to ask it in a new new question and describe your problem. – Nejat Feb 23 '15 at 03:58

score 1 · Answer 3 · answered Jan 04 '15 at 07:52

You can achieve this by editing the java file used by qt itself. In installation path under src in android path you will find QtActivity.java file. In the onCreate function add the below line

getWindow().setFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON, WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);

WAKE_LOCK permission in AndroidManifest.xml also should be added.

Build the project, it will work fine.

How to keep the screen on in Qt for android?

3 Answers3

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