Question

I have custom UIView class GestureView. I have a forward declaration for this class and it’s delegate below. I have imported GestureView.h in .m file. This works fine but iOS gives warning message saying “Cannot find protocol definition for GestureViewDelegate”. If I remove forward declaration it gives same warning message as error. I don’t want to import GestureView.h from ContainerViewController.h as I usually imports stuffs in .m file. Could someone please explain what’s wrong in following class structure?

ContainerViewController.h

#import <UIKit/UIKit.h>

@class DividerView;
@class GestureView;
@protocol GestureViewDelegate;

@interface ContainerViewController : UIViewController<GestureViewDelegate>
   @property (strong, nonatomic) IBOutlet GestureView *topContentView;
@end

GestureView.h

#import <UIKit/UIKit.h>

@protocol GestureViewDelegate;

@interface GestureView : UIView
    - (void)initialiseGestures:(id)delegate;
@end

@protocol GestureViewDelegate <NSObject>
@required
- (void)GestureView:(GestureView*)view handleSignleTap:(UITapGestureRecognizer*)recognizer;
@end

Answer 1

I like that you’re trying to avoid imports in header files: very good practice. However, to fix your bug you can just make your code even better! In my opinion it’s not really necessary that your ContainerViewController class outwardly declares that it supports GestureViewDelegate protocol, so you should move this into your implementation file. Like so:

GestureView.h

#import <UIKit/UIKit.h>


@protocol GestureViewDelegate;

@interface GestureView : UIView

- (void)initialiseGestures:(id <GestureViewDelegate>)delegate;

@end


@protocol GestureViewDelegate <NSObject>
@required

- (void)gestureView:(GestureView *)view handleSingleTap:(UITapGestureRecognizer *)recognizer;

@end

ContainerViewController.h

#import <UIKit/UIKit.h>


@class GestureView;

@interface CollectionViewController : UIViewController

// this property is declared as readonly because external classes don't need to modify the value (I guessed seen as it was an IBOutlet)
@property (strong, nonatomic, readonly) GestureView *topContentView;

@end

ContainerViewController.m

#import "ContainerViewController.h"
#import "GestureView.h"


// this private interface declares that GestureViewDelegate is supported
@interface CollectionViewController () <GestureViewDelegate>

// the view is redeclared in the implementation file as readwrite and IBOutlet
@property (strong, nonatomic) IBOutlet GestureView *topContentView;

@end


@implementation ContainerViewController

// your implementation code goes here

@end