Hi , i finaly found the solution :

i only needed to use the QMdiSubWindow's method : widget() to be able to acess my currently opened widget's methods and signals ...

SO it will become :
Qt Code: 
  1. self.mdiArea.activeSubWindow().widget().update_move_state()
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instead of :
Qt Code: 
  1. self.mdiArea.activeSubWindow().update_move_state()
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