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From: aw@jello.bae.bellcore.com (Andrew Wason)
Newsgroups: comp.windows.x
Subject: Re: Querying the resource database for a child's "requested" resources?
Message-ID: <1991Apr13.045455.13893@bellcore.bellcore.com>
Date: 13 Apr 91 04:54:55 GMT
References: <GNB.91Apr11174058@leo.bby.oz.au>
Sender: usenet@bellcore.bellcore.com (Poster of News)
Reply-To: aw@bae.bellcore.com
Organization: Bell Communications Research
Lines: 83

In article <GNB.91Apr11174058@leo.bby.oz.au>, gnb@bby.oz.au (Gregory N. Bond) writes:
> Consider a subclass of a constraint widget that has three children
> that are created in the parent widget initialize routine.  The three
> children are all the same class, but for one of them I want a
> different default value for a constraint resource.  (i.e. I want
> children 1 and 2 to have "dislpayed: true" and child three to have
> "displayed: false" as the default, where displayed is a constraint
> resource).
> 
> I also want the resource database to be able to override the default,
> as you would expect.
> 
> The default value for the displayed resource is true, so I don't need
> anr args to the create call and children 1 and 2 work as expected -
> they are normally displayed but the user can turn them off.  How can I
> specify the different default constraint resource for the third child?
> If I specify it as an arg to the XtCreateManagedWidget() call, it
> overrides the resource database and the user cannot change the
> setting.

I think you can do this by using XtGetSubresources for
the display resource on widget three.

Create a struct to hold the value of the XtNdisplay resource.
Create a new XtResourceList with one entry for your XtNdisplay resource,
but with default_addr set to False (instead of the normal default of True).
(assume widgets 1,2,3 are of class "Display", class pointer
displayWidgetClass).

  typedef struct {
      Boolean display;
  } ThreeDisplayStruct;
  ThreeDisplayStruct threeDisplay;
  XtResource displayResource[] = {
      { XtNdisplay, XtCDisplay, XtRBoolean, sizeof(Boolean),
        XtOffsetOf(ThreeDisplayStruct, display),
        XtRImmediate, (XtPointer)False }
  };

Now call XtGetSubresources to fetch this resource for your widget
(parent is the constraint parent).

  XtGetSubresources(parent, (caddr_t)&threeDisplay,
                    "three", "Display",
                    displayResource, XtNumber(displayResource),
                    NULL, 0);

Now create your widget using the XtNdisplay resource you just fetched.

  three = XtVaCreateManagedWidget("three",
                                  displayWidgetClass, parent,
                                  XtNdisplay, threeDisplay.display,
                                  NULL);


This would be even simpler if XtNdisplay wasn't a constraint
resource (call it XtNnewDisplay), you could create the widget
first and then refetch the XtNnewDisplay resource directly into the
widget instance record.

  three = XtCreateManagedWidget("three",
                                displayWidgetClass, parent,
                                NULL, 0);
  XtGetSubresources(three, (caddr_t)&three,
                    NULL, NULL,
                    &resources[5], 1,
                    NULL, 0);

Where resources[5] is the entry for XtNnewDisplay in widget threes
resource list (don't try this for callback resources though).


I haven't actually tried any of this, but I think it will work.
Let me know if you try it.


Andrew

_______________________________________________________________________________

Andrew Wason                                       Bell Communications Research
aw@bae.bellcore.com                                Piscataway, NJ
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