@property and @synthesize: why both?

I have been climbing the learning curve of X-code for about two months now. I understand the purpose of the @property/@synthesize directives, but it seems that it is a bit redundant to always declare the properties in the .h file, and then synthesize them in the .m file.

Why does the compiler need both direc开发者_如何学Gotives? If they are always used together, isn't one of them technically redundant?

Thanks in advance for any insights on this subject.

John Doner

The @property (...) foo keyword is used inside your class definition. You don't need to use @synthesize keyword in the implementation file if you provide appropriate getters/setters.

Example:

@property int SomeInt;

---

-(int)SomeInt {
  return _someInt;
}

-(void)setSomeInt:(int)newValue {
  _someInt = newValue;
}

Or you can use either @synthesize foo to inform the compiler to generate getters/setters for you or @dynamic to inform the compiler that these methods will be available at runtime - both in the implementation file.

There's actually more magic behind properties in Objective-C, read up on them at Apple Reference Library.

It's so that you can split implementation and declaration. Seems pretty neat to me.

Well, you can't use @synthesize in category implementations, so that might be one reason.