I tried to change the test's class from QTextEdit and QWidget and it actually works!
But... I think I have some focus problem, 'cause in my main class it doesn't work.

I tried to set focuspolicy to tabfocus, focus to tabfocusreason, with no advantage.
I tried grabkeyboard() but it says
Qt Code: 
  1. X Error: BadWindow (invalid Window parameter) 3
  2.   Major opcode: 31 (X_GrabKeyboard)
  3.   Resource id:  0x0
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what could I do?