Major_Project_B/Assets/Scripts/UI/Dragable.cs

using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

[RequireComponent(typeof(Image))]
public class Dragable : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{
    protected GameObject m_DraggingIcon;
    protected RectTransform m_DraggingPlane;

    public virtual void OnBeginDrag(PointerEventData eventData)
    {
        var canvas = FindInParents<Canvas>(gameObject);
        if (canvas == null)
            return;

        // We have clicked something that can be dragged.
        // What we want to do is create an icon for this.
        m_DraggingIcon = new GameObject("icon");

        m_DraggingIcon.transform.SetParent(canvas.transform, false);
        m_DraggingIcon.transform.SetAsLastSibling();
        m_DraggingIcon.layer = LayerMask.NameToLayer("Ignore Raycast");

        var image = m_DraggingIcon.AddComponent<Image>();

        image.sprite = GetComponent<Image>().sprite;
        image.SetNativeSize();


        m_DraggingPlane = canvas.transform as RectTransform;

        SetDraggedPosition(eventData);
    }

    public virtual void OnDrag(PointerEventData data)
    {
        if (m_DraggingIcon != null)
            SetDraggedPosition(data);
    }

    protected virtual void SetDraggedPosition(PointerEventData data)
    {
        var rt = m_DraggingIcon.GetComponent<RectTransform>();
        Vector3 globalMousePos;
        if (RectTransformUtility.ScreenPointToWorldPointInRectangle(m_DraggingPlane, data.position, data.pressEventCamera, out globalMousePos))
        {
            rt.position = globalMousePos;
            rt.rotation = m_DraggingPlane.rotation;
        }
    }

    public virtual void OnEndDrag(PointerEventData eventData)
    {
        Destroy(m_DraggingIcon);
        m_DraggingIcon = null;
    }

    static public T FindInParents<T>(GameObject go) where T : Component
    {
        if (go == null) return null;
        var comp = go.GetComponent<T>();

        if (comp != null)
            return comp;

        Transform t = go.transform.parent;
        while (t != null && comp == null)
        {
            comp = t.gameObject.GetComponent<T>();
            t = t.parent;
        }
        return comp;
    }
}