Volume 6A: Motif Programming Manual

void

file_cb(widget, client_data, call_data)

Widget widget;

XtPointer client_data;

XtPointer call_data;

{

extern void OpenNewFile(), SaveFile();

int item_no = (int) client_data;

if (item_no == 0) /* the "new" button */

OpenNewFile ();

else if (item_no == 1) /* the "save" button */

SaveFile();

else /* the "Quit" button */

exit (0);

}

The callback routines for menu items should be as simple as possible from a structural point of view. A well−designed

application should have application−specific entry points such as OpenNewFile() and SaveFile(), as shown in

the previous example. These routines should be defined in separate files that are not necessarily associated with the

user−interface portion of the program. The use of modular programming techniques helps considerably when an

application is being maintained by a large group of people or when it needs to be ported to other user−interface

platforms.

5.2.3 A Sample Application

Let's examine an example program that integrates what we have discussed so far. Example 4−3 modifies the behavior

of our first example, which displayed an arbitrary pixmap, by allowing the user to change the bitmap dynamically

using a Motif FileSelectionDialog. The program also allows the user to dynamically change the color of the bitmap

using a PulldownMenu. As you can see by the size of the program, adding these two simple features is not trivial.

Many functions and widgets are required in order to make the program functional. As you read the example, don't

worry ...