c# - WPF : control visibility does not render in a command after the first time -

working on mvvm wpf form.

i'm using relaycommand to:

1) change control visibility

2) run long process

3) update control's visibility back

command code follows:

    private relaycommand _mycommand;     public relaycommand mycommand     {                 {             return _mycommand                 ?? (_mycommand = new relaycommand(                 () =>                 {                         //1 update control's visibility                         gridviewvisibility = false;                           //deleting reference done via multithreading process quite long (10 sec)                         task.run(() =>                         {                              application.current.dispatcher.invoke((new action(() =>                             {                                 //2 looong process here                                   //3 update control's visibility                                 gridviewvisibility = true;                             }                        )));                         }                         );                  } ));         }     } 

systematically, when run command first time, works perfectly. controls visibility updates expected (before , after process).

but when trigger command again, operation 2 still performed. code updates visibility reached not render (1 , 3). control's visibility not updated.

any idea why????