Volume 6A: Motif Programming Manual

User interface of tree.uil

The syntax of the Panner and Tree widget definitions is almost the same as the many Motif widget definitions that

you've already seen. The main difference is that you replace the Motif widget class name with user_defined

procedure followed by the name of the widget creation procedure. To reference a user−defined widget in the

controls subsection of a widget, you just use the keyword user_defined followed by the name of the widget.

You can mix user−defined resources and built−in resources as in the Panner definition, which contains some of its

own resource settings as well as a couple of Form constraint resource settings. You can also specify user−defined

resource names in the arguments subsection of a built−in widget definition. For example, the Label widget children

of the Tree contain resource settings for the user−defined XtNtreeParent resource. The Panner widget contains a

user−defined callback setting; the pan() callback routine is invoked when the user adjusts the Panner. The syntax of

using user−defined resources and callbacks is the same as that for built−in resources and callbacks. The main

drawback of user−defined widgets is that, unlike with the built−in Motif widgets, the compiler does not know which

resources are valid for the widget, so it lets you set any resources. This generally is not a problem when you are only

working with a few user−defined widgets, ...