There are a several interfaces that you can utilize in your VBA programs to receive notification when certain things happen in MicroStation. See the IPrimitiveCommandEvents description for more details. Other methods are called at similar times. When the class implementing this interface is activated, the IPrimitiveCommandEvents_Start method is called first, which usually places a prompt message in the status bar area. The IPrimitiveCommandEvents interface says the class behaves like a MicroStation tool such as Place Arc or Place Circle (both “primitive” command tools because they place primitive elements). To conclude, the use of an interface tells MicroStation that the class has methods to call in certain circumstances, and that the class behaves in a particular way. For an example of implementing this interface, see the Element Creation Command example.

MicroStation calls each of these methods by name when the actions of the user dictate. These methods allow your VBA program to respond to each of the events necessary to create and place a design element in the active model. The class then must provide code for each of the six methods in the PrimitiveCommand interface.

The Implements statement to inform MicroStation that a class is going to provide code for the IPrimitiveCommandEvents interface looks like this: The Implements statement, used to declare that a class is making use of an interface, is really a contract that states the class is going to provide code for each of the methods of the interface. A missing member of an interface will cause an error in compilation. Since an interface is really a collection of prototypes for the methods and properties of a class, it is necessary for a class that “implements” the interface to duplicate all of the Public methods declared as part of the interface.

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