Question

I am developing a simple set of reusable code. I have created a protocol to group a set of methods and ask the user at run time for data.

I think that setting a delegate would be mandatory. Can I force the developer at runtime to set the delegate by throwing an assert stating the reason?

Is this a good practice to enforce the user of my classes by using asserts? Does it have a design level flaw?

Answer 1

First the “good practice” question:

• Don’t make methods required unless they actually are.

• Don’t make methods optional if they aren’t.

• Not a critical one, more of an opinion

  • Provide a method initWithDelegate: if a delegate is required
  • I often come across data structures where I don’t know that there is a delegate pattern until I investigate. With the specific init method, I’m made aware of it earlier.

You can cause warnings at compile time by simply adding the @required indicator to your protocol:

@protocol SuperAwesomeProtocol <NSObject>

@required
-(void) requiredMethod1;
-(void) requiredMethod2;

@optional
-(void) optionalMethod1;
-(void) optionalMethod2;

@end

//and making your delegate specific:
@property (nonatomic, assign) id<SuperAwesomeProtocol> delegate;

You can still cause runtime asserts with:

if (!delegate || ![delegate respondsToSelector:@selector(requiredMethod1)])
{
    //Assertion failure
}