Relationship between interface and class definitions in objective-c

Question

The following is my AppDelegate.h file:

#import <UIKit/UIKit.h>    

@class ViewController;  

@interface AppDelegate : UIResponder <UIApplicationDelegate>    
@property (strong, nonatomic) UIWindow *window;
@property (strong, nonatomic) ViewController *viewController;

@end

The following is a file called ViewControllerTEST.h containing the declaration of the ViewController interface used by AppDelegate.h:

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController

@end

My question:

How does the compiler know where to find the declaration for the ViewController interface when "@class ViewController" line in AppDelegate.h is ran? In other words, how did the compiler know that the interface for the ViewController class is defined in ViewControllerTEST.h when it's executing the line "@class ViewController" in AppDelegate.h?

Answer 1

It looks like someone renamed the file that is now called ViewControllerTEST.h file. It was most probably originally called ViewController.h.

By default, if your header or implementation file has a line like the following: "@interface ViewController : ..." then the actual .h or .m file will be named ViewController.h or ViewController.m. Such is the case when you create a new class (File -> New -> File -> Objective C Class).

Anyway, you can actually change the filenames of these .h and .m files after creating them and still maintain the connections (don't forget to change the corresponding "#import ..." portion in the .m file though). What's important is that you do not change the controller name in the "@interface ..." and "@implementation ..." portions so that they are two differently named view controllers. This will yield errors in Xcode.

Having said all of this, Xcode keeps track of the actual class name ("ViewController") when you first created the class. Unless you perform Refactor in Xcode, which is not an important topic at this point in your learning.

Hope this helps...