无法找到协议声明 - iOS

Question

当我尝试在以下两个类中使用协议时，编译器说无法找到协议声明

的ViewController：

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

@protocol FlipOtherSideViewControllerDelegate;

@interface ViewController : UIViewController<FlipsideViewControllerDelegate>     {
    id <FlipOtherSideViewControllerDelegate> __unsafe_unretained delegate;
}

- (IBAction)switchMode:(id)sender;
@property (unsafe_unretained) id <FlipOtherSideViewControllerDelegate> delegate;

@end

 @protocol FlipOtherSideViewControllerDelegate
- (void)flipothersideViewControllerDidFinish:(ViewController *)controller;
 @end

SecondViewController：

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

@protocol FlipsideViewControllerDelegate;

@interface SecondViewController : UIViewController   <FlipOtherSideViewControllerDelegate> {
id <FlipsideViewControllerDelegate> __unsafe_unretained delegate;
}

@property (unsafe_unretained) id <FlipsideViewControllerDelegate> delegate;
@end

@protocol FlipsideViewControllerDelegate
- (void)flipsideViewControllerDidFinish:(SecondViewController *)controller;
@end

上述任何建议？ 提前致谢。

Answer 1

为什么在界面下方声明？尝试在接口声明之前声明。我认为那时不应该有任何错误。