forward protocol @required to subclasses

I have:

@interface SuperClass : UIViewController <UITableViewDelegate,UITableViewDataSource>

And then

@interface SubClass : SuperClass

This SuperClassdoes not have the required protocol methods implemented SubClass one does.开发者_StackOverflow

Is it possible to prevent the warnings (saying SuperClass implementation is incomplete)?

Instead of implementing empty/nil methods in SuperClass, can the @required warnings validation be made against SubClass?

You might not declare protocol adoption in the superclass, but demand compliance in all subclasses. This can be done by implementing +initialize in your superclass as follows:

+ (void)initialize
{
  if (self != [SuperClass class] && 
      ![self conformsToProtocol:@protocol(UITableViewDelegate)])
  {
    @throw [NSException ...]
  }
}

That way, whenever a subclass of SuperClass is initialized, it will throw an exception if it doesn't conform to <UITableViewDelegate>. This requires no further work after putting this in the superclass.

No, what you're asking for is essentially abstract classes, which don't exist in Objective-C.

Your best bet is to stub the methods in the base class to throw an exception of some kind.

If SuperClass is not conform to the UITableViewDelegate, etc. protocols it should not have it in the .h.

You can simply move the protocols to SubClass.

Yes this is possible using a private class extension.

Example 1

Superclass.h

@interface Superclass : UIViewController
@end

Superclass.m

@interface Superclass()<UITableViewDelegate, UITableViewDataSource>
@end

@implementation Superclass
// implement interface methods
@end

Subclass.h

@interface Subclass : Superclass<UITableViewDelegate, UITableViewDataSource>
@end

Taking it a step further, you could move the private class extension into a private header Superclass+Private.h then your other internal classes can know it implements them too.

Example 2

Superclass+Private.h

#import "Superclass.h"

@interface Superclass()<UITableViewDelegate, UITableViewDataSource>
@end

Superclass.m

#import "Superclass+Private.h>

@implementation Superclass
// implement interface methods
@end

Note There is a limitation that this technique prevents you overriding and calling super in method that the subclass does not its super class has implemented. For those methods I would recommend the UIGestureRecogniser subclass pattern.