Unity - Detect input on canvas elements using EventSystem event interfaces (e.g. IPointerClickHandler) -- via: http://answers.unity.com/answers/1095070/view.html

PointerExample.cs

 using UnityEngine;
 using UnityEngine.EventSystems; // 1
 
 public class PointerExample : MonoBehaviour
     , IPointerClickHandler // 2
     , IDragHandler
     , IPointerEnterHandler
     , IPointerExitHandler
 // ... And many more available!
 {
     SpriteRenderer sprite;
     Color target = Color.red;
 
     void Awake()
     {
         sprite = GetComponent<SpriteRenderer>();
     }
 
     void Update()
     {
         if (sprite)
             sprite.color = Vector4.MoveTowards(sprite.color, target, Time.deltaTime * 10);
     }
 
     public void OnPointerClick(PointerEventData eventData) // 3
     {
         print("I was clicked");
         target = Color.blue;
     }
 
     public void OnDrag(PointerEventData eventData)
     {
         print("I'm being dragged!");
         target = Color.magenta;
     }
 
     public void OnPointerEnter(PointerEventData eventData)
     {
         target = Color.green;
     }
 
     public void OnPointerExit(PointerEventData eventData)
     {
         target = Color.red;
     }
 }