I was hoping to make an app which dimmed the soft buttons to dots on the Galaxy Nexus, using the code from this answer. For completeness, this is the code:
getWindow().getDecorView().setSystemUiVisibility(View.SYSTEM_UI_FLAG_LOW_PROFILE);
Here's the question, is it possible for the app to make this setting system-wide rather than just while the app has focus? So ideally the app would run in the background and would keep View.SYSTEM_UI_FLAG_LOW_PROFILE as the default as long as it's running, for any and every app that you open (unless that app specifically overrides it, I suppose). Is this possible or does this fall outside the realm of what an Android app has permission to do?
A sample use case is this: I use the "Screen Filter" app to reduce brightness a lot for nighttime ebook reading or misc app usage, but the soft buttons are still very bright and distracting, so I wanted to make an app that would dim the soft buttons system-wide while running (like how "Screen Brightness" reduces screen brightness system-wide while running) so this wouldn't be a problem.
As CommonsWare states, it's not possible for an application to change this setting. It's an Activity based setting, that must be set for every single Activity, if you want to make it fullscreen, hide the soft keys, etc.
It's also worth pointing out that you should probably refrain from using it in all your application activities. It's really only meant for games, video players and other applications that need to enter this "low profile" state.
Feel free to accept CommonsWare's answer - I just thought I'd give you a bit of background info on the subject.
is it possible for the app to make this setting system-wide rather than just while the app has focus?
No.
来源：https://stackoverflow.com/questions/8660638/possible-to-make-setsystemuivisibility-affect-the-entire-system-rather-than-j