:
step1: write a class A interface inheritance IExternalCommandAvailability, implement the method returns true.
2: When applied to the menu, Pushbutton .AvailabilityClassName = the full name A.
:
step1: write a class A interface inheritance IExternalCommandAvailability, implement the method returns true.
2: When applied to the menu, Pushbutton .AvailabilityClassName = the full name A.