Two questions about objective-c: framework link and "self" in dot & square bracket expression

I am learning iphone dev now. Now I am reading book "iPhone 4 Development". During reading this book, I am confused about some syntax about objective-c used in this book. Ok, here are my questions:

• Link framework v.s. header file

At the end of chapter 7 of this book, the book mentions "link project to framework". In this book, it links to project to AudioToolbox.framework. I am wondering why not just add the header file instead of linking framework? What's the difference between linking to a framework and adding a header file?

• "self" in dot & "[]" expression

In chapter 9 of this book, sample code uses dot operator and square bracket expression several times, for example: SecondLevelViewController *controller = [controllers objectAtIndex:row]; and SecondLevelViewController *nextController = [self.controllers objec开发者_C百科tAtIndex:row]; I think these two sentences have the same function. So when should I use "self"? When not?

Thanks, Sam

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Linking framework, just as in Visual Studio for Windows, tells your compiler where to find the libraries.

You then add the relevant include/import calls so that the compiler finds your class from imported library in the source, goes up the import/include, goes and hits the library, and back (more or less, it doesn't matter the exact behavior).

The question about self is a clear duplicate, check SO for "objective-c self"...

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When you write self.outlet = nil the method [self setOutlet:nil]; is called. When you write outlet = nil; you access variable outlet directly.

if you use @synthesize outlet; then method setOutlet: is generated automatically and it releases object before assigning new one if you declined property as @property (retain) NSObject outlet;.

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