I have create a delegate in our custom UIView, here is the code:

@protocol CustomViewDelegate
@optional
- (void) CustomViewDidInitialize:(CustomView *)customView;
@end
 
@interface CustomView : UIView {    
@private
}
@property(nonatomic, assign) id<CustomViewDelegate> delegate;
@end

The above code is not working because the CustomView interface has not been declared at the time of the CustomViewDelegate declaration.
So, now I tried it by adding a prototype ala C++ before the @protocol like this:

@interface FunView;

But it's also not solving my problem, so anyone have the solution then please tell me, thank you.