Many GUI applications have a single, main form for the application. When the application starts, the form is displayed and when the form is closed, the application terminates. When the application waits on a main or MDI form, the ABL WAIT-FOR statement must specify Application:Run( ) with the main form passed in as a parameter. This starts a .NET message loop which is used to capture events and run ABL event handlers.

This is an example of the WAIT-FOR statement for an application that has a single, main form:

WAIT-FOR Application:Run( FormObjectRef ).

When the main form FormObjectRef is specified in the WAIT-FOR statement, the form is displayed when the message loop is started.

Closing the main form terminates the WAIT-FOR. This continues execution in the current block in your program immediately after the WAIT-FOR. The application can close the main form by calling the Close( ) method on FormObjectRef.