9.2 An example interface

Here is a simple example of interface definition done with define-interface :

(define-interface demo ()

  ()

  (:panes

   (page-up push-button 

            :text "Page Up")

   (page-down push-button

              :text "Page Down")

   (open-file push-button

              :text "Open File"))

  (:layouts

   (row-of-buttons row-layout

                   '(page-up page-down open-file)))

  (:default-initargs :title "Demo"))

An instance of this interface can be displayed as follows:

At the moment the buttons do nothing, but they will eventually do the following:

• Open File will bring up a file prompter and allow you to select a filename from a directory. Later on, we will add an editor pane to display the chosen file's contents.
• Page Down will scroll downwards so that you can view the lower parts of the file that cannot be seen initially.
• Page Up will scroll upwards so that you can return to parts of the file seen before.

Figure 9.1 A demonstration of a CAPI interface

Later on, we will specify callbacks for these buttons to provide this functionality.

The (:default-initargs :title "Demo") part at the end is necessary to give the interface a title. If no title is given, the default name is "Untitled CAPI Interface".

Note: the define-interface form could be generated by the Interface Builder tool in the LispWorks IDE. See the LispWorks IDE User Guide for details. As the interface becomes more complex, you will find it more convenient to edit the definition by hand.

9.2.1 How the example works