title: Error in updating the score in a game
body: <p>I have problem when i updating score in the game i make i dont know what is the problem but when i shoot something the score should increment by 1 but in my code sometimes it increment by 2 or 3 sometimes 1 it not constant i dont know why this happen here is the code i used </p>
  
  <pre><code>@interface GameScene () {
  
      SKLabelNode* _scoreLabelNode;
      NSInteger _score;
  
  
  }
  
  
  -(void)didMoveToView:(SKView *)view {
  
      _score = 0;
          _scoreLabelNode = [SKLabelNode labelNodeWithFontNamed:@"Silom Regular"];
          _scoreLabelNode.fontSize = 50;
          _scoreLabelNode.position = CGPointMake(self.size.width - 335 , self.size.height - 60);
          _scoreLabelNode.zPosition = 100;
          [self addChild:_scoreLabelNode];
  
          _scoreLabelNode.text = [NSString stringWithFormat:@"%d",_score];
  }
  
  if (contact.bodyB.categoryBitMask == ObjectCategory) {
  
          _score++;
          _scoreLabelNode.text = [NSString stringWithFormat:@"%d",_score];
  }
  </code></pre>