Path: utzoo!attcan!uunet!tank!ncar!mailrus!cornell!batcomputer!gdykes
From: gdykes@batcomputer.tn.cornell.edu (Gene Dykes)
Newsgroups: comp.windows.x
Subject: Handles for Public Functions
Message-ID: <7098@batcomputer.tn.cornell.edu>
Date: 3 Jan 89 18:10:38 GMT
Distribution: comp
Organization: Theory Center, Cornell U., Ithaca NY
Lines: 34


I would appreciate comments on the following problem and my solution to it:

I have a widget layout manager that parses a grammar that describes a widget
tree.  It is no trouble to specify resources in this grammar, because widgets
use string "handles" for the resources.  Thus, an entry in the grammar might
look like this:

    foreground "blue"

But I would also like to specify "actions" in this grammar, one type of which
is to call a widget's public function.  The problem is that widgets don't
have any handles defined for public functions; the client has to call the
public function directly by its true name.  Consider the following grammar
line:

    XtFormDoLayout (Form "form1", Boolean "True")

This describes a call to a public function of the Xaw "Form" widget.
The layout manager can construct the arguments from the text, but it
has no handle on the address of the function to call.

There are two solutions to this problem.  The first is to hardwire a table
of tags and functions into the manager.  This is, of course, not very
desirable.  My solution is to require widgets with public functions that
desire to be "nice" widgets to return a list of tags and function addresses
as the value of a resource (I chose "XtNpublicFunctions").

It's fairly trivial to add this to widgets contributed from other sources,
but it seems that perhaps it should have some kind of official
blessing :-) or condemnation :-(.

-- 
Gene Dykes, gdykes@tcgould.tn.cornell.edu