QuickTime Kit Programming Guide - filibeto.org

C H A P T E R 4
Adding New Capabilities to the QTKitPlayer Application
3. Add a larger chunk of code to your MovieDocument.m implementation file. This will involve
working with a callback mechanism from the QuickTime C API. The goal is to learn how you can
tap into the rich library of the QuickTime C API, when you want to add specific functionality to
your Cocoa project that may not be available, for whatever reason, in the Cocoa API.
Project Complexity
The complexity of the project comes with the addition of a callback mechanism from the QuickTime
C API.
Basically, as the movie is playing, you need a mechanism to update the timer field in the drawer. The
movie controller component calls your action filter function each time the component receives an
action for its movie controller. In your action filter, you will use the idle action (mcActionIdle) to
update your time display. The idle action is sent continuously while the movie is being serviced.
You could do a similar thing with an NSTimer, but the action filter technique is a bit easier to implement.
The function prototype for the QuickTime C callback mechanism is defined as follows:
Boolean MyMCActionFilterWithRefConProc
( MovieController mc,
short action,
void *params,
long refCon );
The MyMCActionFilterWithRefConProc function responds to the actions of a movie controller with
a reference constant. The parameters specify the movie controller (mc) for the operation, the movie
controller action (action), a pointer to a structure that passes information to the callback, and a
reference constant (refCon) that your code supplies to your callback. Your QTKitPlayer application
can invoke these actions by calling MCDoAction. An action filter function will receive any of the
controller actions sent to it.
You’ll add this callback to the code in your MovieDocument.m implementation file. The way to
accomplish this is explained in detail in the section “Adding Code To Make the Drawer Work” (page
73).
Class Model
When you’ve completed all these tasks, you’ll see the class model of your QTKitPlayer code in Xcode
2.0, as shown in Figure 4-3. The class model includes a list of the MovieDocument instance variables
you’ll add to your QTKitPlayer project and a visualization of their connections and inheritance paths.
Tasks to Accomplish 63
2005-11-09 | © 2004, 2005 Apple Computer, Inc. All Rights Reserved.