Release 10.1A: OpenEdge Development:
Programming Interfaces

4GL mechanisms

Ultimately, the differences between COM objects and widgets require separate but related mechanisms in the 4GL to work with them. The most fundamental of these mechanisms are the handles you use to access COM objects and widgets. You must access widgets with widget handles and COM objects with component handles. These handles have different data types that represent the different capabilities that they support—the WIDGET-HANDLE data type for widget handles and the COMPONENT-HANDLE (or COM-HANDLE) data type for COM objects.

COM-HANDLE values have a data type that is compatible with most other Progress data types. For component handles, Progress does the data conversion automatically, unlike widget handles which require the use of Progress data conversion functions, like STRING or INTEGER.

Table 14–1 compares each type of object (COM object and Progress widget) and summarizes how it is supported in the 4GL.

Table 14–1: COM objects and Progress widgets compared 

Feature	COM object support	Progress widget support
Compilation	No compile-time checking.	Compile-time checking for attribute and method references.
Instantiation	Dynamic, with different mechanisms for Automation objects and ActiveX controls.	Static or Dynamic, depending on the widget and application.
Handle type	COM-HANDLE.	WIDGET-HANDLE.
Handle validity	VALID-HANDLE function.	VALID-HANDLE function.
Access to data	Properties (optionally indexed).	Attributes.
Access to behavior	Methods (with unnamed parameters).	Methods (with unnamed parameters).
Access to events	Event procedures (with unnamed parameters).	Triggers.
Integration with 4GL data	Extensive automatic mapping between COM data types and Progress data types.	Full integration with Progress data types and 4GL data management.
Color management	RGB color values (RGB-VALUE function, GET-RGB-VALUE method on the COLOR-TABLE system handle).	Index numbers of RGB color values in the Progress color table (COLOR-TABLE system handle).
Dynamic object management	RELEASE OBJECT statement.	DELETE Widget statement.

For more information on Progress widgets and the 4GL mechanisms for managing them, see the information on widgets and handles in OpenEdge Development: Progress 4GL Handbook . The rest of this chapter describes the equivalent mechanisms that support COM objects.