1) The Qt provided "screenshot" sample code demonstrates the failing grabWindow() behavior seen elsewhere on multiple Android platforms (have not yet found one that it works on). QScreen::grabWindow() always returns a null bitmap on Android.  See function shootScreen() in the Qt sample code.

2) Attempts to use grabWindow() all fail on Android (Win32 works fine).

• fails on NVIDIA Shield K1 (arm) running either Android 6 or 7.
• fails on Panasonic FZ-B2D (x86) running Android 6.0.1
• fails on ACER (x86) GT-810 running Android 5.1
• fails on Juniper Systems Cedar (ARM) GT7G 7" running Android 6.0 

3 Tried various permutations of winId()'s, screen geometry rect's, default parameters to try and find something combination that works.  No joy (but it all works on Windows, not Android).

grabWindow(0)

grabWindow(QApplication:desktop()->winID());

grabWindow(QApplication.activeWindow()-winId(), rect.x(), rect.y()...).  etc...