unity2D touch drag

hi friends, I want to make a game in which I am instantiating many objects I want them to be able to move when the user touch and drag any of these. If user drags say sprite1 then only sprite1 should move, no else. I am using this code but when I run it on android application exits, it may have some errors. please help me to get a working script. `using UnityEngine; using System.Collections;

public class Text : MonoBehaviour { public float speed = 1F; void Update() { Vector2 rray = Camera.main.ScreenToWorldPoint(Input.GetTouch(0).position); RaycastHit2D hit; if (Physics2D.Raycast (rray, Vector2.zero)) { if (Input.touchCount > 0 && Input.GetTouch (0).phase == TouchPhase.Moved) { Vector2 touchDeltaPosition = Input.GetTouch (0).deltaPosition; hit.transform.Translate (touchDeltaPosition.x speed, touchDeltaPosition.y speed, 0); } } } }`