Inside Macintosh: More Macintosh Toolbox
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In general, when using Component Manager routines, your application must specify the particular component using either a component identifier or component instance. The Component Manager identifies each component by a component identifier. The Component Manager identifies each instance of a component by a component instance. Thus, when your application searches for a component with a particular type and subtype using the FindNextComponent function, FindNextComponent returns a component identifier that identifies the component. Similarly, your application specifies a component identifier to the GetComponentInfo function to obtain information about a component.
When you open a connection to a component, the OpenDefaultComponent and OpenComponent functions return a component instance. The returned component instance identifies that specific instance of the component. If you open the same component again, the Component Manager returns a different component instance. So a component has a single component identifier and can have multiple component instances. To use a component function, your application specifies a component instance.
Although conceptually component identifiers and component instances serve different purposes, Component Manager routines (with the exception of DelegateComponentCall ) allow you to use component identifiers and component instances interchangeably. If you do this, you must always coerce the data type appropriately.
A component identifier is defined by the data type Component :
TYPE
{component identifier}
Component = ^ComponentRecord;
ComponentRecord =
RECORD
data: ARRAY[0..0] OF LongInt;
END;
A component instance is defined by the data type ComponentInstance :
TYPE
{component instance}
ComponentInstance = ^ComponentInstanceRecord;
ComponentInstanceRecord =
RECORD
data: ARRAY[0..0] OF LongInt;
END;