Beginning Mac OS® X Programming

A.9. Chapter 9

A.9.1. Exercise 1 solution

You can solve this problem either by reusing the existing MainEventHandler or by creating a new event handler. The solution that follows extends MainEventHandler.

1. In Xcode, replace main.c's call to InstallWindowEventHandler with the following code:

   // Install the window event handler
       EventTypeSpec eventSpec[2] = {
           {kEventClassKeyboard, kEventRawKeyDown},
           {kEventClassCommand, kEventCommandProcess},
       };
       InstallWindowEventHandler(window,
                                 NewEventHandlerUPP(MainEventHandler),
                                 2,
                                 eventSpec,
                                 (void*)window,
                                 NULL);

2. Replace the entire MainEventHandler with the following code:

   OSStatus MainEventHandler(EventHandlerCallRef handler, EventRef event, void *userData)
   {
       OSStatus result = eventNotHandledErr;
   
       UInt32 class = GetEventClass(event);
   
       if (class == kEventClassCommand) {

   HICommand command;
   
           // get the HICommand from the event
           GetEventParameter(event,
                             kEventParamDirectObject,
                             typeHICommand,
                             NULL,
                             sizeof(HICommand),
                             NULL,
                             &command);
   
           // if this is a compute event regenerate the result string
           if (command.commandID == kComputeResultCmd) {
               ComputeResult((WindowRef)userData);
               result = noErr;
           }
       }
   
       // if this is a keyboard event, forward the event first, and then
       // recompute the events
       else if (class == kEventClassKeyboard) {
           // forward the event
           result = CallNextEventHandler(handler, event);
   
           // if the event was handled correctly, compute the result
           if (result == noErr) {
               ComputeResult((WindowRef)userData);
           }
       }
   
       return result;
   }

3. Save your changes to main.c ...