Callback Procedures

Enterfunctions do nothing but gather data, they are service layer functions and are used by higher level procedures, such as adding a polygon to a database cell. To allow the higher level procedures to respond to or to monitor the progress of the enterfunction, callback procedures should be supplied to the enterfunction.

These procedures are not required, but allow an application to trap a condition as soon as the condition becomes known. This prevents having to enter twenty points of a shape, only to find that the second point caused a problem. The enterfunctions can have registered callback procedures that are invoked for the following events:

• The enterfunction is starting
• A point is entered
• A point is deleted
• The enterfunction is finished or canceled

These functions are known as the initProc, addPointProc, delPointProc, formProc, and doneProc.

Do not call finishEnterFun or cancelEnterFun from within any of the callback procedures.