If SysHandleEvent() didn't handle the event, it's passed to MenuHandleEvent(). Again a system API, it handles such as tapping on the menu key or selecting a menu item.

If still not handled, the event loop passes the event to ApplicationHandleEvent(). This is the first user-defined event handler. Typically it checks for only "load form" events; setting a form event handler for the specified form. Usually each form has its own event handler.

Finally, if the event still hasn't been handled, it is given to FrmDispatchEvent(). Another OS API, it sends the event to the appropriate event handler for the active form. That's the one set when ApplicationHandleEvent() handles the "load form" event. The form-event-handler watches for any events where we should actually do work. For example, our main-form-specific handler handles the button-press event that causes us to display "hello again!"

It's a bit convoluted. Just remember that the event loop gets an event, passes it to several event handlers, and one of them handles the event. The form-specific handler handles the events that make us do real work.

Function 5: ApplicationHandleEvent()
Our ApplicationHandleEvent() indeed does handle just one event: frmLoadEvent, a message from the OS indicating we're loading a new form. Getting the form ID number from the event structure, we tell Palm OS to initialize and activate that form. Then, we tell the OS which event handler to use for that form's events. Again, that's the handler called when the event loop passes an event to FrmDispatchEvent().

Function 6: MainFormHandleEvent()
This is where we watch for events and do real work. Ours handles three types of events:

• frmOpenEvent tells us the form is active - we can now draw it. So we do; we get a pointer to the form, and tell the OS to draw that form on the display. Palm OS draws the form and its controls.

• ctlSelectEvent tells us a control has been "selected" - in our case; the "hello again" button was pushed. We check the button ID number (given in the event structure); if it's the "hello again" button, we draw "hello again" on the form. WinDrawChars() puts the text onto the display (onto the current form); most of the line is to calculate where to place it so it's centered.

• menuEvent tells us that a menu item was selected. Usually what we do depends on the menu item's ID number. We're told that in the event structure. Since we know there's only one menu option ("about") we take a shortcut. With only one choice, we just do the work. First, we tell the menu to go away, then switch to our AboutForm (by its form ID number). We treat it here as a special dialog; we'll cover this in more detail in another article. In short, it displays the AboutForm and when the user presses the AboutForm's "ok" button it closes that form. The key is that nothing can happen except pressing a button to close the form. That's why I didn't do the whole "hello world" application as a special dialog.