ABL mechanisms

Ultimately, the differences between COM objects and widgets require separate but related mechanisms in ABL 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 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 ABL data types. For component handles, ABL does the data conversion automatically, unlike widget handles which require the use of ABL data conversion functions, like STRING or INTEGER.

Table 59. COM objects and ABL widgets compared
Feature	COM object support	ABL 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	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 ABL data	Extensive automatic mapping between COM data types and ABL data types	Full integration with ABL data types and ABL 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 ABL color table (COLOR-TABLE system handle)
Dynamic object management	RELEASE OBJECT statement	DELETE Widget statement