Palm Programming: The Developer's Guide

Scenarios

Now that you have a better understanding of the code in the Hello World application, let’s take a close look at what happens as events are passed from the event queue into the event loop. Unlike our earlier example, where we hand-waved through the technical parts of what happens when a menu was chosen, we will now look with great detail at three different user actions and the flow through the code as these scenarios occur.

This first code excerpt shows what happens when a user opens the application by tapping on the application’s icon. Example 4.9 shows the flow of events. Pay particular attention to the frmLoadEvent , which is handled by ApplicationHandleEvent , and the frmOpenEvent, which is handled by MyFormHandleEvent.

Example 4-9. Flow of Control as Hello World Application Is Opened

PilotMain (enter)
  StartApplication (enter)
    FrmGotoForm(HelloWorldForm)                  open the HelloWorldForm
  StartApplication (exit)                        returns 0 (proceed)
  EventLoop (enter)
  EvtGetEvent                                    returns frmLoadEvent (formID 
                                                     HelloWorldForm)
    SysHandleEvent                               returns false
    MenuHandleEvent                              returns false
    ApplicationHandleEvent (enter)
      FrmInitForm(HelloWorldForm)                load the form
      FrmSetActiveForm(frm)                      activate the form
      FrmSetEventHandler(frm, MyFormHandleEvent) set the event handler
    ApplicationHandleEvent (exit)                returns true
  EvtGetEvent                                    returns frmOpenEvent
  SysHandleEvent                                 returns false
  MenuHandleEvent                                returns false
  ApplicationHandleEvent                         returns false
  FrmDispatchEvent (enter)                       calls form's event handler MyFormHandleEvent (enter) ...