客观C - 无法识别的代表

Question

我是Objective C的新手，并试图理解代表的概念。我有下面的代码，并且已经在构建中发生警告和错误的地方发表了评论。我正在使用最新版本的Xcode并使用Storyboard。

从MainViewController.h

#import <UIKit/UIKit.h> 
#import "FinalViewController.h" 

@class MainViewController; 
@protocol MainViewControllerDelegate <NSObject> 
- (void)sayHello; 
@end 

@interface MainViewController : UIViewController 
@property (nonatomic, strong) id <MainViewControllerDelegate> delegate; 
- (void)writeToMe; 
. . . 
@end 

从MainViewController.m

#import "MainViewController.h" 
#import "FinalViewController.h" 
@interface MainViewController() 
@end 

@implementation MainViewController 
- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 
} 

- (void)writeToMe 
{ 
    [self.delegate sayHello]; 
} 
. . . 
@end 

从FinalViewController.h

#import <UIKit/UIKit.h> 
#import "MainViewController.h" 

@interface FinalViewController : UIViewController <NSCoding, MainViewController> //The ERROR below appears 
    //ERROR:Cannot find protocol declaration for ‘MainViewControllerDelegate’; did you mean ‘UIPageViewControllerDelegate’? 
    . . . 
@end 

从FinalViewController.m

#import "FinalViewController.h" 
@interface FinalViewController() 
@end 

@implementation FinalViewController 
- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 
    MainViewController *mainVC; 
    mainVC.delegate = self; //causes WARNING below 
    //WARNING:Assigning to ‘id <MainViewControllerDelegate> from incompatible type ‘FinalViewController *const__strong’ 

    [mainVC writeToMe]; 
    . . . 
} 

- (void)sayHello 
{ 
    NSLog(@"sayHello called"); 
} 
@end 

我已经研究了这个网站上类似问题的问题和反应，但还没有找到使用Storyboard的解决方案。

Answer 1

变化：

#import "MainViewController.h" 
#import "FinalViewController.h" 
@interface MainViewController() 
@end 

@implementation MainViewController 
- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 
} 

- (void)writeToMe 
{ 
    [self.delegate sayHello]; 
} 
. . . 

TO：

#import "MainViewController.h" 
@interface MainViewController() 
@end 

@implementation MainViewController 
- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 
} 

- (void)writeToMe 
{ 
    [self.delegate sayHello]; 
} 
. . . 

ALSO：

#import <UIKit/UIKit.h> 
#import "FinalViewController.h" 

@class MainViewController; 
@protocol MainViewControllerDelegate <NSObject> 
- (void)sayHello; 
@end 

@interface MainViewController : UIViewController 
@property (nonatomic, strong) id <MainViewControllerDelegate> delegate; 
- (void)writeToMe; 
. . . 
@end 

TO

#import <UIKit/UIKit.h> 


@protocol MainViewControllerDelegate <NSObject> 
- (void)sayHello; 
@end 

@interface MainViewController : UIViewController 
@property (nonatomic, weak) id <MainViewControllerDelegate> delegate; 
- (void)writeToMe; 
. . . 
@end 

---------------------------编辑--------------------- ---------------

变化

@interface FinalViewController : UIViewController <NSCoding, MainViewController> 

到

@interface FinalViewController : UIViewController <NSCoding, MainViewControllerDelegate> 

Answer 2

这可能是一个错字，但：

@interface FinalViewController : UIViewController <NSCoding, MainViewController> 

应be：

@interface FinalViewController : UIViewController <NSCoding, MainViewControllerDelegate> 

还从MainViewController.h删除"FinalViewController.h"的导入。

和你其他的警告可以通过改变固定：

@interface FinalViewController() 

到：

@interface FinalViewController() < MFMailComposeViewControllerDelegate> 

和变化：

mainVC.delegate = self; 

到：

mainVC.mailComposeDelegate = self;