Delegate for the iOS

Question

I'm trying to see why the type can't be read from the protocol. I figured that the it's because the @interface is below the protocol but if someone can help me figure out the problem and explain to me why that would be great.

#import <UIKit/UIKit.h>

@protocol ARCHCounterWidgetDelegate <NSObject>

    - (UIColor *) counterWidget: (ARCHCounterWidget *) counterWidget;

@end

@interface ARCHCounterWidget : UIView

    @property (weak, nonatomic) id<ARCHCounterWidgetDelegate> delegate;

@end

Answer 1

You have to either forward declare the class or the protocol:

// tell the compiler, that this class exists and is declared later:
@class ARCHCounterWidget;

// use it in this protocol
@protocol ARCHCounterWidgetDelegate <NSObject>
- (UIColor *) counterWidget: (ARCHCounterWidget *) counterWidget;
@end

// finally declare it
@interface ARCHCounterWidget : UIView
@property (weak, nonatomic) id<ARCHCounterWidgetDelegate> delegate;
@end

or:

// tell the compiler, that this protocol exists and is declared later
@protocol ARCHCounterWidgetDelegate;

// now you can use it in your class interface
@interface ARCHCounterWidget : UIView
@property (weak, nonatomic) id<ARCHCounterWidgetDelegate> delegate;
@end

// and declare it here
@protocol ARCHCounterWidgetDelegate <NSObject>
- (UIColor *) counterWidget: (ARCHCounterWidget *) counterWidget;
@end

Answer 2

The compiler is not yet aware of the ARCHCounterWidget, and therefore cannot resolve the type in the delegate method. Simple solution is:

#import <UIKit/UIKit.h>

// Reference the protocol
@protocol ARCHCounterWidgetDelegate

// Declare your class
@interface ARCHCounterWidget : UIView

    @property (weak, nonatomic) id<ARCHCounterWidgetDelegate> delegate;

@end

// Declare the protocol
@protocol ARCHCounterWidgetDelegate <NSObject>

    - (UIColor *) counterWidget: (ARCHCounterWidget *) counterWidget;

@end

It just makes it so that the compiler knows that the protocol is defined SOMEWHERE and can be referenced