Free Drag Drop Item Script for uGUI Unity C#

DragDropItem.cs

// Canvase should be Screen Space - Camera
// Attach a Event Trigger Script to image you want to Drag Drop
// Add Begin Drag and Drap Event Listener
// Attach this script to that image

using UnityEngine;
using UnityEngine.UI;
using System.Collections;
using UnityEngine.EventSystems;

public class DragDropItem : MonoBehaviour
{
  // To keep track of drag position
	private Vector2 prevDragPos;

	public void OnDragBegin(BaseEventData data) {
    // 0- Save Begin drag position to use it OnDrag
		prevDragPos = getScreenPosition ();
	}
	
	public void OnDrag (BaseEventData data)
	{
		// 1- Get current position on screen
		Vector3 point = getScreenPosition ();
		
		// 2- Calc difference of movement with prev Drag pos
		float x = point.x - prevDragPos.x;
		float y = point.y - prevDragPos.y;
		
		// 3- Assign difference to current object's Transform
		Vector3 resPos = transform.position;
		resPos.x += x;
		resPos.y += y;
		transform.position = resPos;
		
		// 4- Now current Drag position become prev one
		prevDragPos = point;
	}
	
	private static Vector3 getScreenPosition ()
	{
		// Get current position on screen
		Vector3 curPos = Camera.main.ScreenToWorldPoint (Input.mousePosition);
		curPos.z = 0;
		return curPos;
	}
}