Xcode - ติดปัญหา cannot find protocol declaration ??

@protocol TTDelegate <NSObject>
///
@end

@interface TT : NSObject
{
      __weak id<TTDelegate> tdelegate;
}
@property (nonatomic, weak) id <TTDelegate> tdelegate;

#import <UIKit/UIKit.h>
#import "TestViewController.h"
#import "TT.h"


@interface ViewController : UIViewController<TTDelegate>
{

}