导入协议时没有类型或协议错误

Question

At first, in LoadingVC.h I declare a protocol:

@protocol VideoWorker <NSObject>

@required

@property (nonatomic) float progress;
@property (nonatomic) BOOL done;

-(void)beginWorking;

@end

@interface LoadingVC : UIViewController <UIAlertViewDelegate>
...
@end

then in BlurWorkerGPU.h

...
#import "LoadingVC.h"

@interface BlurWorkerGPU  : NSObject <VideoWorker> {
...
}
- (void)beginWorking;
@property(nonatomic)float progress;
@property(nonatomic)BOOL done;
 ...
@end

However, llvm says that

"No type or protocol named 'VideoWorker'"

which is strange since I am importing the header where the protocol is defined. Any clues?

Answer 1

You should forward declare protocol in .h files before you use it. Put this in the top of BlurWorkerGPU.h

@protocol VideoWorker;

Answer 2

检查是否在“LoadingVC.h”中导入“BlurWorkerGPU.h”

Answer 3

Possible solutions are

• import protocol

@import YOURPROTOCOLNAME

• import Class in which protocol is declared

#import "YOURCLASSWHICHDECLAREDPROTOCOL.h"

• Use @Class to import the class

@class YOURCLASSWHICHDECLAREDPROTOCOL;