[vtkusers] A mistake

[JohnMark]

Hi,
I am writing a program by vtkSphereWidget ( using C++ ) ,and I want to connect my render window with the mouse event , so I use the AddObserver() function , at the same time , I write a new function that could be invoked , its name is MyFunction() . As the usage of AddObserver() , my code is : 
        sphereWidget->AddObserver( InteractionEvent, MyFunction );
but there is a error : 'unsigned long __thiscall vtkObject::AddObserver(unsigned long,class vtkCommand *,float)' : cannot convert parameter 2 from 'void' to 'class vtkCommand *' .
So why is it ? and how can I use the AddObserver() ? Could you give me an example ? thank you !
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