Thank you so much for your answer ZikO !! It works perfectly... (OMG, I lost half a day with this trouble...)

Also, thank you very much for your advice... In fact, 'columns_number' could change during the execution, because it is the column number of the main Qtable of the application, and the ComboBox is used to setup each column, so I'm going to use your second initialisation !!

Thanks for all !!

Best Regards,

Stéphane