title: use of undeclared identifier in Xcode
body: <p>I'm making an simple game, and Xcode finds a bug says that there is a "use of undeclared identifier 'gameLoop'". How can I fix this?</p>
  
  <pre><code>// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
  
  
  (void)viewDidLoad {
      [super viewDidLoad];
      gameState = kStateRunning;
  
  
      [NSTimer scheduledTimerWithTimeInterval: 1.0/60 target:self selector:@selector(gameLoop) userInfo:nil repeats:YES];
      rockVelocity = CGPointMake (0, 0); 
      gravity = CGPointMake (0, kGravity);    
  
  - (void)gameLoop {
      if (gameState == kStateRunning)
      {
          [self gameStatePlayNormal];
      }
      else if (gameState == kStateGameOver)
      {
  
      }
  }
  
  (void)gameStatePlayNormal {
      rockVelocity.y += gravity.y;
  
      rock.center = CGPoint(rock.center.x + ballVelocity.x,rock.center.y + rockVelocity.y);
  </code></pre>