Question

I just don’t understand why some guys declare the methods in the .m file. Can’t those declarations just go in the .h file instead?? Here’s what I see mostly:

//myClass.h

#import <UIKit/UIKit.h>

@interface myClass: UIViewController
{

}

@end

And the implementation (.m) part:

//myClass.m

#import "myClass.h"

@interface myClass

//declare some methods here

@end

@implementation myClass

//the actual implementation

@end

Is there any difference when the methods are declared this way?? Also, “@private” methods can be declared in myClass.h itself, can’t they?

Answer 1

The code you have posted both doesn’t compile and isn’t equivalent to declaring methods in the header.

The purpose of the header is to provide a set of declarations that other classes can import. They can’t import your implementation file, because that will create duplicate definitions.

As bbum said, what you’re probably seeing is private method declarations in the implementation file. These aren’t intended to be used outside the class, so they’re declared in the implementation file. The feature is called a class extension:

//MyClass.h

#import <UIKit/UIKit.h>

@interface MyClass: UIViewController

// Declare methods that other classes should call here

@end

//MyClass.m

#import "MyClass.h"

@interface MyClass () // <--- NOTE THE PARENTHESES HERE

// Declare methods that only this class should be using here

@end

@implementation MyClass

// Define all your methods here

@end

And no, you can’t declare “@private methods” in the header, or anywhere else. There’s no such thing in Objective-C. The @private access specifier only applies to variables.