我正在努力实现以下目标:一名球员因重力坠落self.physicsWorld.gravity=CGVectorMake(0,-4.0);当用户触摸屏幕时,播放器应该上升-(void)update:(CFTimeInterval)currentTime{if(self.isAscending){CGVectorrelativeVelocity=CGVectorMake(0,400-self.playerNode.physicsBody.velocity.dy);self.playerNode.physicsBody.velocity=CGVectorMake(0,self.playerN