Actually i already tried grabKeyboard() before creating this thread. It was working on my desktop and i wasn't sure if it'll work on the embedded device properly.
But i just tested in on the device and it seems to work

The problem was getting the Window Deactivation event on the embedded device. The device doesn't have a window manager so i don't get any event when user clicks outside the window. So, i tried trapping FocusOut event instead and it's working fine.

I had some -ve thoughts about grabKeyboard that if i do grabKeyboard on my main widget in the Qt window, it won't allow me to transfer focus to other widgets, but it's working fine.