The application determines what documents to open when they are dropped on
the application icon. There is an FREF resource which now has two main
functions for an application:
- Associates the icons defined with file types used by that application.
- Allows you to drag document icons to an application icon to open the
documents from that application.
An application should create an FREF resource for the application file
itself, and create separate FREF resources for each file type that the
application can open. Each FREF resource specifies a file type. The file
type can be defined for:
- Files created by that application only
- Files created by other applications that the application supports
- Files of the existing general types, such as TEXT or PICT
When you drag a document icon to an application icon, the Finder checks a
list of that application's FREF resources. If the document's file type
appears in the FREF resource list, the Finder launches that application
with a request to open that document. It's up to the application to open
the files according to the needs of the user.
An alias should act the same way as the original it was created from, as
the file type will be the same. If you're having problems launching a
document alias created by the application you're dragging the alias to,
rebuild the Desktop.
There is further information in Chapter 9 (Finder Interface) of Inside
Macintosh VI.