DEC Text Processing Utility Program Development

5.2Programming in DECwindows DECTPU

5.2.4.4Internally Defined DECTPU Callback Routines with Widgets Not Defined by UIL

Although the SET (WIDGET) built-in procedure lets you specify values for various resources of a widget, there are restrictions on specifying values for callback resources of widgets. When a widget is not part of an X Resource Manager hierarchy, specify the names of the callback resources in the array you pass to SET (WIDGET), and specify 0 as the value of each such callback resource. DECTPU automatically substitutes its common callback entry point for the 0 value. A widget calls back only for those reasons specified in the widget’s argument list. If a reason is omitted from the list, the corresponding event does not cause a callback.

5.2.4.5 Application-Level Callback Action Routines

When DECTPU receives a widget callback, it identifies and executes the layered application procedure or learn sequence that has been designated as the callback action routine. You can designate a procedure or learn sequence as a callback action routine either when the widget is created, by using the CREATE_WIDGET built-in procedure, or at some later time, by using the SET (WIDGET_CALLBACK) built-in procedure. When you specify an application-level callback program or learn sequence with CREATE_WIDGET or SET (WIDGET_ CALLBACK), all widgets in the same X Resource Manager hierarchy have the same callback program or learn sequence. Therefore, the callback program or learn sequence must have a mechanism for handling all possible callback reasons.

5.2.4.6 Callable Interface-Level Callback Routines

If you are layering an application on DECTPU or on EVE, you can specify callable interface-level callback routines only if you are specifying a widget’s callback resources in a User Interface Language (UIL) file.

Callbacks can pass values known as closures. Closures are strings or integers whose function depends on the application you are writing. (DECwindows documentation refers to closures as tags.) For more information about what closures are and how to use them, see Section 5.2.5.

You use the DECTPU callable interface routine TPU$WIDGET_INTEGER_ CALLBACK as the callback routine for all callbacks that have an integer closure. You use the DECTPU routine TPU$WIDGET_STRING_CALLBACK for all callbacks that have a string closure.

When a widget is part of an X Resource Manager hierarchy, do not include callback resource names or values in the array you pass to SET (WIDGET). Instead, specify the callback routine in the UIL file. When a widget is not part of an X Resource Manager hierarchy, specify the names of the callback resources in the array you pass to SET (WIDGET), and specify 0 as the value of each such callback resource. DECTPU automatically substitutes its common callback entry point for the 0 value. A widget calls back only for those reasons specified in the widget’s argument list. If a reason is omitted from the list, the corresponding event does not cause a callback.

DEC Text Processing Utility Program Development 5–9

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Compaq AA-PWCBD-TE manual Application-Level Callback Action Routines, Callable Interface-Level Callback Routines
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