title: SKSpriteNode subclass and touches events
body: <p>I can't understand why if I subclass a SKSpriteNode, that implements the UIResponder protocol, the methods related with touches are never been called.</p>
  
  <p>For example, this is a really simple class that I'm using as test:</p>
  
  <pre><code>//INTERFACE ----------------
  #import &lt;SpriteKit/SpriteKit.h&gt;
  
  @interface TestClass : SKSpriteNode
  
  @end
  
  //IMPLEMENTATION -----------
  #import "TestClass.h"
  
  @implementation TestClass
  
  
  - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{
       NSLog(@"oook");
  }
  
  - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{}
  - (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{}
  - (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event{}
  
  @end
  </code></pre>
  
  <p>If I attach an instance of this class to the scene, touching the object... nothing happens. </p>
  
  <p>Am I forgetting something? </p>