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just a simple question : if you write a method in the .h file, you don't "have" to write the implementation in the .m file? i discovered that with FlipsideViewController, if you create a new projet (utility application), the method : "flipsideViewControllerDidFinish" is actually "implemented" in the "MainViewController.m". i just wanted to have this clear, thanks for your answer ;)

Paul

Paul
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  • It's a protocol (see Caleb's answer below). But even if it wasn't, yes you could declare a method in the header and not implement it. But then it would crash at runtime. Which would not be a good thing. ;) – FeifanZ Jul 05 '11 at 15:12

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FlipsideViewControllerDelegate is a protocol declared in FlipsideViewController.h and adopted by (implemented in) MainViewController. The main view controller needs to know when the flip side controller is done, but it doesn't make sense for FlipsideViewController to know specifics about MainViewController. All it needs to know is that there's an object that it's supposed to notify when it's done, and that that object implements the methods in the FlipsideViewControllerDelegate protocol. This is the delegation pattern: read more about it in How Delegation Works.

Caleb
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  • Exactly—notice that the methods are enclosed in a block beginning with `@protocol` and ending with `@end`. That's an Objective-C protocol. – FeifanZ Jul 05 '11 at 15:11