Unity3D中UGUI图片拖动换图效果。

在Canvas上添加两个图片Image,分别是原图 和 目标图，准备将原图用鼠标点击拖到目标图上释放。然后目标图上的图就变为原图了。

原图上挂载如下脚本DragMe.cs：

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

[RequireComponent(typeof(Image))]
public class DragMe : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{
    public bool dragOnSurfaces = true;
    
    private Dictionary m_DraggingIcons = new Dictionary();
    private Dictionary m_DraggingPlanes = new Dictionary();

    public void OnBeginDrag(PointerEventData eventData)
    {
        var canvas = FindInParents(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_DraggingIcons[eventData.pointerId] = new GameObject("icon");

        m_DraggingIcons[eventData.pointerId].transform.SetParent (canvas.transform, false);
        m_DraggingIcons[eventData.pointerId].transform.SetAsLastSibling();
        
        var image = m_DraggingIcons[eventData.pointerId].AddComponent();
        // The icon will be under the cursor.
        // We want it to be ignored by the event system.
        var group = m_DraggingIcons[eventData.pointerId].AddComponent();
        group.blocksRaycasts = false;

        image.sprite = GetComponent().sprite;
        image.SetNativeSize();
        
        if (dragOnSurfaces)
            m_DraggingPlanes[eventData.pointerId] = transform as RectTransform;
        else
            m_DraggingPlanes[eventData.pointerId]  = canvas.transform as RectTransform;
        
        SetDraggedPosition(eventData);
    }

    public void OnDrag(PointerEventData eventData)
    {
        if (m_DraggingIcons[eventData.pointerId] != null)
            SetDraggedPosition(eventData);
    }

    private void SetDraggedPosition(PointerEventData eventData)
    {
        if (dragOnSurfaces && eventData.pointerEnter != null && eventData.pointerEnter.transform as RectTransform != null)
            m_DraggingPlanes[eventData.pointerId] = eventData.pointerEnter.transform as RectTransform;
        
        var rt = m_DraggingIcons[eventData.pointerId].GetComponent();
        Vector3 globalMousePos;
        if (RectTransformUtility.ScreenPointToWorldPointInRectangle(m_DraggingPlanes[eventData.pointerId], eventData.position, eventData.pressEventCamera, out globalMousePos))
        {
            rt.position = globalMousePos;
            rt.rotation = m_DraggingPlanes[eventData.pointerId].rotation;
        }
    }

    public void OnEndDrag(PointerEventData eventData)
    {
        if (m_DraggingIcons[eventData.pointerId] != null)
            Destroy(m_DraggingIcons[eventData.pointerId]);

        m_DraggingIcons[eventData.pointerId] = null;
    }

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

        if (comp != null)
            return comp;
        
        var t = go.transform.parent;
        while (t != null && comp == null)
        {
            comp = t.gameObject.GetComponent();
            t = t.parent;
        }
        return comp;
    }
}
 

 

将目标图片上挂载如下脚本DropMe.cs：

using System.Reflection;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

public class DropMe : MonoBehaviour, IDropHandler, IPointerEnterHandler, IPointerExitHandler
{
    public Image containerImage;
    public Image receivingImage;
    private Color normalColor;
    public Color highlightColor = Color.yellow;
    
    public void OnEnable ()
    {
        if (containerImage != null)
            normalColor = containerImage.color;
    }
    
    public void OnDrop(PointerEventData data)
    {
        Debug.Log("OnDrop()");
        containerImage.color = normalColor;
        
        if (receivingImage == null)
            return;
        
        Sprite dropSprite = GetDropSprite (data);
        if (dropSprite != null)
            receivingImage.overrideSprite = dropSprite;
    }

    public void OnPointerEnter(PointerEventData data)
    {
        if (containerImage == null)
            return;

        Sprite dropSprite = GetDropSprite(data);
        if (dropSprite != null)
            containerImage.color = highlightColor;
    }

    public void OnPointerExit(PointerEventData data)
    {
        if (containerImage == null)
            return;

        containerImage.color = normalColor;
    }
    
    private Sprite GetDropSprite(PointerEventData data)
    {
        var originalObj = data.pointerDrag;
        if (originalObj == null)
            return null;
        
        var dragMe = originalObj.GetComponent();
        if (dragMe == null)
            return null;
        
        var srcImage = originalObj.GetComponent();
        if (srcImage == null)
            return null;
        
        return srcImage.sprite;
    }
}