异常＆＃39; NSInvalidArgumentException＆＃39;，原因：＆＃39; - [SIGameScene setDelegate：]：

Question

请帮忙！ 我有这个错误，应用程序在模拟器和设备上运行... 是什么原因 ？

SIgameScene.h代码：

@interface SIGameScene : SKScene {
    BOOL gameRunning;
    double gameStartedAt;
    NSTimer *timer;
    int lifes;
    int level;

}

@property (strong, nonatomic) SKSpriteNode *background;
@property (strong, nonatomic) SKSpriteNode *spaceship;
@property (strong, nonatomic) NSMutableArray *projectilesFriendly;
@property (strong, nonatomic) NSMutableArray *projectilesEnemy;
@property (strong, nonatomic) NSMutableArray *invaders;

@property (weak, nonatomic) id <SIGameSceneDelegate, SKSceneDelegate> delegate;

- (void)startGame;
- (void)pauseGame;
- (void)stopGame;
- (void)moveSpaceshipSidewaysByAngle:(double)angleInDegrees;

@end