Objective-C Fundamentals

150 CHAPTER 7 Protocols
The first thing this code does is fill in the applicationDidFinishLaunching method,
which is part of the UIApplicationDelegate protocol. In here you create a button
that calls another method you’ll define. You create the myView object and set the
myView delegate to this class B. Then you add the view into your window. Next you
make a button in code c. This is the button you’ll tap to call the animate method in
myView d. With this done, you must make a method that tells myView to animate
when the button is pressed. The code is short—check it out; this should be added as a
method to myProtocolAppDelegate.m:
- (void)animate {
[view animate];
}
This code calls the animate method in myView. All that’s left to do is define the protocol
methods and implement what you want them to do. For this example, two things
happen when the animation starts, as shown in the following listing.
Listing 7.7 Filling in myProtocolAppDelegate.m, part 2
- (void)animationStartedWithView:(UIView*)animatedView {
NSLog(@"The animation has started");
[animatedView setBackgroundColor:[UIColor whiteColor]];
}
Fire up the simulator and see this in action. If your terminal is up, you can see the log
messages as well. You’ve successfully defined and implemented a custom protocol.
7.3 Important protocols
Now that you’ve seen all the guts of making and implementing a protocol, let’s look at
the most popular protocols used in the development of an iPhone application. Apple
relies on the protocol design method for many of its Cocoa classes. In this section we
review four sets of protocols that you’ll likely use when developing your application.
Let’s dive in.
7.3.1
Write a log
message
Set background to white
- (void)animationHasFinishedWithView:(UIView*)animatedView {
NSLog(@"The animation has finished");
Write a log message
[animatedView setBackgroundColor:[UIColor blackColor]];
}
Set background
- (void)dealloc {
to black
[view release];
[window release];
[super dealloc];
}
@end
The UITableViewDataSource protocol is a mandatory protocol to have implemented
for any table view in your application. A table view is a visual element that’s meant to
display some collection of information. Unlike any other user interface element in the