void OnTriggerEnter2D(Collider2D collisionObject) not working with drag object to the trigger

Hi
i am creating 2D game to drag letters and put them in the right order or place and make some action when put them in the correct order like sound .Anyway , i am using trigger so when i drag the letter to that trigger, it should give me that sound, but it doesn't. unless i use Rigidbody 2D property the letter (which i dont want to use Rigidbody).

this is the code i use for the trigger:

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class GameTrigger1_1 : MonoBehaviour {
5.     public AudioClip au;
6.         public void OnTriggerEnter2D(Collider2D collisionObject){
7.         if (string.Equals (collisionObject.tag, "D")) {
8.                     audio.PlayOneShot(au);
9.                 }                  
10.    
11.         }
12.    
13. }

i already give the letter BoxCollider 2D property, and i dont know its not working and give me any output while i drag the letter to the trigger, looking for your help

thanks

 

I'm not pro, but just giving my 2 cents, did you tick the checkbox for isTrigger for your collider?
Also, to see if it is actually colliding, try using debug.log ("test message") in your code.