Question

I have helper class which contain different methods. I dо not want to include it’s header file at every class that I have in my app. That approach is against DNRY I think.
Here is why I decide to create one “master” class called AppController and each class in my app to inherit it.

Here is what I do

AppController.h

#import <Foundation/Foundation.h>
#import "Helper.h"

@interface AppController : NSObject
{
  ivars...
}
 some methods ...
@end;

myClass.h

import "AppController.h"

@interface myClass : AppController
{
 ivars...
}
some methods
@end

So far, so good.
The problem rise when some class needs to inherit not NSObject, but let’s say UIViewController. This is the moment where my AppController become useless.
I know that Objective-c is not support multiple inheritance. I have read somewhere that can be done using composition, but I can’t figure out how to do that.
I will be grateful if someone gives me some examples.

Answer 1

I have read somewhere that can be done using composition, but I can’t figure out how to do that. I will be grateful if someone gives me some examples.

Yes, composition is how you do this. Your inheritance approach is wrong on several levels.

• Your class called “AppController” is not a proper class. It captures unrelated functionality. A class should do one thing.
• You’re forcing an awkward inheritance tree
• You’ve called it “app controller” which is already the name of an important object in Cocoa.

Here is how you approach this:

• First, split up your functions and methods into related groups. You should not have one giant “utility” class. Import these functions and methods into the things that need them, not every class in the system.
• Use categories to attach new utility functionality to existing classes (including system classes).
• Consider functions rather than methods for many utility-like things (but still, split them up into related files, not one giant “Utility.m”).

The vast majority of things people would normally use a “utility” dumping ground for are better solved with categories and functions in ObjC. The remainder are usually best served using delegation (but that’s another topic).