ItemData Script

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

public class ItemData : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler, IPointerDownHandler {

    public Item item;
    public int amount;
    public int slot;

    private Inventory inv;
    private Tooltip tooltip;
    private Vector2 offset;

    void Start() {

        inv = GameObject.Find("Inventory").GetComponent<Inventory>();
        tooltip = inv.GetComponent<Tooltip> ();

    }

    public void OnPointerDown (PointerEventData eventData) {

        if (item != null) {
            offset = eventData.position - new Vector2 (this.transform.position.x, this.transform.position.y);
            tooltip.Activate (item);
        }

    }

    public void OnBeginDrag (PointerEventData eventData) {

        if (item != null) {
            if (Input.GetMouseButton (0) && !Input.GetMouseButton (1) && !Input.GetMouseButton (2)) {
                Debug.Log ("Left Mouse Button Down");
                this.transform.SetParent (this.transform.parent.parent.parent);
                this.transform.position = eventData.position - offset;
                GetComponent<CanvasGroup> ().blocksRaycasts = false;
            }
            else if (!Input.GetMouseButton (0) && Input.GetMouseButton (1) && !Input.GetMouseButton (2)) {
                Debug.Log ("Right Mouse Button Down");
                this.transform.SetParent (this.transform.parent.parent.parent);
                this.transform.position = eventData.position - offset;
                GetComponent<CanvasGroup> ().blocksRaycasts = false;
            }
            else if (!Input.GetMouseButton (0) && !Input.GetMouseButton (1) && Input.GetMouseButton (2)) {
                Debug.Log ("Middle Mouse Button Down");
                this.transform.SetParent (this.transform.parent.parent.parent);
                this.transform.position = eventData.position - offset;
                GetComponent<CanvasGroup> ().blocksRaycasts = false;
            }
        }
    }

    public void OnDrag (PointerEventData eventData) {

        if (item != null) {
            this.transform.position = eventData.position - offset;
        }

    }

    public void OnEndDrag (PointerEventData eventData) {

        this.transform.SetParent(inv.inventorySlots[slot].transform);
        this.transform.position = inv.inventorySlots[slot].transform.position;
        GetComponent<CanvasGroup>().blocksRaycasts = true;

    }
}