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?

Answer 1

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);
        }
    }
}

Answer 2

1. Use window.callMethod<void> instead of window.callObjectMethod
2. Run on GUI thread with QtAndroid::runOnAndroidThread
3. Clear exceptions afterwards
4. 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();
    }
  });
}

Answer 3

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.