Programming the ActiveX control

You make an ActiveX control do its job by programming it in scripts, setting its properties, and calling its functions. Depending on the interface provided by the ActiveX control developer, a single function call might trigger a whole series of activities or individual property settings, and function calls may let you control every aspect of its actions.

An ActiveX control is always active—it does not contain an object that needs to be opened or activated. The user does not double-click and start an OLE server. However, you can program the DoubleClicked or any other event to call a function that starts ActiveX control processing.

Programming an ActiveX control is the same as programming automation for insertable objects. You use the container’s Object property to address the properties and functions of the ActiveX control.

This syntax accesses a property value. You can use it wherever you use an expression. Its datatype is Any. When the expression is evaluated, its value has the datatype of the control property:

olecontrol.Object.ocxproperty

This syntax calls a function. You can capture its return value in a variable of the appropriate datatype:

{ value } = olecontrol.Object.ocxfunction ( { argumentlist } )

The PowerBuilder compiler does not know the correct syntax for accessing properties and functions of an ActiveX control, so it does not check any syntax after the Object property. This provides the flexibility you need to program any ActiveX control. But it also leaves an application open to runtime errors if the properties and functions are misnamed or missing.

PowerBuilder provides two events (ExternalException and Error) for handling OLE errors. If the ActiveX control defines a stock error event, the PowerBuilder OLE control container has an additional event, ocx_event. These events allow you to intercept and handle errors without invoking the SystemError event and terminating the application. You can also use a TRY-CATCH exception handler.

An ActiveX control has its own set of events, which PowerBuilder merges with the events for the custom control container. The ActiveX control events appear in the Event List view with the PowerBuilder events. You write scripts for ActiveX control events in PowerScript and use the Object property to refer to ActiveX control properties and methods, just as you do for PowerBuilder event scripts.

The only difference between ActiveX control events and PowerBuilder events is where to find documentation about when the events get triggered. The ActiveX control provider supplies the documentation for its events, properties, and functions.