title: OnCollisionEnter2D of unity dont appears
body: <p>When i try to use OnCollisionEnter2D, is like this function don't exists in MonoBehaviour, i try to digit On + CRTL+ SPACEBAR and the only things that appears is CommonOnScreenControl,ReadOnlyCollectionBase,RuntimeInitializeOnLoadMethodAttribute.</p>
  
  <p>My objects have a box collider 2d and a Rigid body (with body type Dynamic and discrete continuous collision detect)</p>