title: Drop Event not firing with IDropHandler in Unity3D
body: <p>I have 2 prefabs objects consisting in a panel with UI.Text inside. One contains the class for dragging and the other the dropping. However, even if the drag works fine the OnDrop() function is never executed. I have also set the blockRaycasts to false in the CanvasGroup that I added to the main Canvas. </p>
  
  <pre><code> GetComponentInParent&lt;CanvasGroup&gt;().blocksRaycasts = false;
  </code></pre>
  
  <p>Are there any reasons why the method OnDrop() implemented from the interface UnityEngine.EventSystems.IDropHandler may not be firing while I'm dragging an object into it?</p>
  
  <pre><code>public class ItemDropHandler : MonoBehaviour, IDropHandler
  {
      public void OnDrop(PointerEventData eventData)
      {
          Debug.Log("Drop detected over the UI.Text"); //this is never shown
      }
  }
  </code></pre>