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?

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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.

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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.

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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.

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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.