ScreentoWorldPoint not working for UI Object?

I have this code:

Code (CSharp):

1.    
2. private GameObject draggedObject = null;
3. void Update () {
4.         if(Input.GetMouseButton(0))
5.         {
6.             RaycastHit2D hit = Physics2D.Raycast(Camera.main.ScreenToWorldPoint(Input.mousePosition), Vector2.zero);
7.  
8.             if(hit.collider)
9.             {
10.                 if(draggedObject == null)
11.                 {
12.                     Debug.Log("hello");
13.                 }
14.             }
15.         }
16. }

The problem is that the mouse seems don't register the collider while clicking object under UI Canvas.
If I put those objects outside canvas, then it work.

How to fix this?

Thank you

 

Does the object you're trying to click have a collider?

 

Yes

 

Have you tried this tutorial?

I used to use this, but I now use TouchScript from the Asset Store. It's really really good. Would defo suggest it .