Unity编辑器拓展：使用DragAndDrop拓展Hierarchy窗口拖拽处理

下面将利用UnityEditor下的DragAndDrop类拓展Hierarchy窗口下的两种功能。

主要使用其静态方法 AddDropHandler(HierarchyDropHandler handler)

Unity版本：2021.3.23f1c1

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一、实现将Assets中的脚本文件拖拽到Hierarchy窗口下，则直接创建一个空物体并加上此脚本关联的组件。

效果：

实现代码：（放Editor文件夹下） 

using UnityEditor;
using UnityEngine;

[InitializeOnLoad]
public class DropMonoScriptToHierarchy
{
    static DropMonoScriptToHierarchy()
    {
        DragAndDrop.AddDropHandler(HierarchyDropHandler);
    }

    private static DragAndDropVisualMode HierarchyDropHandler(int dropTargetInstanceID, HierarchyDropFlags dropMode, Transform parentForDraggedObjects, bool perform)
    {
        Object obj = EditorUtility.InstanceIDToObject(dropTargetInstanceID);//拖拽放置目标对象
        if (!perform)//在拖拽中时
        {
            //仅支持拖拽1个脚本文件
            if (DragAndDrop.objectReferences.Length == 1 && DragAndDrop.objectReferences[0] is MonoScript script)
            {
                if (obj == null)
                    return DragAndDropVisualMode.Generic;//放置目标为空时，改变VisualMode
            }
        }
        else//在拖拽放下时
        {
            if (DragAndDrop.objectReferences.Length == 1 && DragAndDrop.objectReferences[0] is MonoScript script && obj == null)
            {
                if (typeof(Component).IsAssignableFrom(script.GetClass()))//判定脚本文件的类型是否为组件
                    Selection.activeObject = new GameObject(script.GetClass().Name, script.GetClass());//创建新物体，并加组件
                else
                    Debug.Log($"非组件脚本文件：{script.name}");
            }
        }
        return DragAndDropVisualMode.None;
    }
}

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二、将Assets中的Sprite文件拖拽到Hierarchy窗口下的RectTransform对象下，则直接创建一个子RectTransform对象，加上Image组件（sprite设定为拖拽的对象）。

由于Unity将Sprite拖拽到Hierarchy只能创建SpriteRenderer对象，于是做此拓展以实现在UGUI下快速创建Iamge并关联对应的Sprite，同时执行一次SetNativeSize()以调整RectTransform的size与sprite的宽高一致。

 实现代码：（放Editor文件夹下） 

using System.Collections.Generic;
using System.Linq;
using UnityEditor;
using UnityEngine;
using UnityEngine.Events;
using UnityEngine.UI;

[InitializeOnLoad]
public class DropSpriteToHierarchy
{
    static DropSpriteToHierarchy()
    {
        DragAndDrop.AddDropHandler(HierarchyDropHandler);
    }

    private static DragAndDropVisualMode HierarchyDropHandler(int dropTargetInstanceID, HierarchyDropFlags dropMode, Transform parentForDraggedObjects, bool perform)
    {
        if (perform)//在拖拽放下时
        {
            GameObject obj = EditorUtility.InstanceIDToObject(dropTargetInstanceID) as GameObject;//拖拽放置目标对象
            if (obj && obj.transform is RectTransform)
            {
                //拖拽的对象，均应为 Sprite 或着 TextureType为Sprite的Texture2D
                bool allIsSpr = DragAndDrop.objectReferences.All(v => CheckIsSprite(v));
                if (allIsSpr)
                {
                    List<Object> selObjs = new List<Object>(DragAndDrop.objectReferences.Length);

                    UnityAction<Sprite> creatFun = (Sprite dragObj) =>
                    {
                        var newObj = new GameObject(dragObj.name, typeof(RectTransform), typeof(Image));
                        newObj.transform.parent = obj.transform;
                        newObj.transform.localPosition = Vector3.zero;
                        newObj.GetComponent<Image>().sprite = dragObj;
                        newObj.GetComponent<Image>().SetNativeSize();
                        selObjs.Add(newObj);
                    };

                    foreach (var dragObj in DragAndDrop.objectReferences)
                    {
                        if (dragObj is Sprite)
                        {
                            creatFun(dragObj as Sprite);
                            continue;
                        }
                        // 获取选中 Texture2D 对应的路径
                        string assetPath = AssetDatabase.GetAssetPath(dragObj);
                        // 加载所有嵌套在 Texture2D 资源中的 Sprite
                        Object[] sprites = AssetDatabase.LoadAllAssetRepresentationsAtPath(assetPath);
                        // 检查是否存在 Sprite
                        foreach (Object t2d in sprites)
                        {
                            if (t2d is Sprite)
                            {
                                creatFun(t2d as Sprite);
                            }
                        }
                    }

                    Selection.objects = selObjs.ToArray();

                    return DragAndDropVisualMode.Generic;
                }
            }
        }
        return DragAndDropVisualMode.None;
    }

    public static bool CheckIsSprite(Object tarObj)
    {
        if (tarObj is Sprite || tarObj is Texture2D)
        {
            return true;
        }
        //else if (tarObj is Texture2D)
        //{
        //    // 获取该Texture的Importer
        //    string path = AssetDatabase.GetAssetPath(tarObj);
        //    TextureImporter importer = AssetImporter.GetAtPath(path) as TextureImporter;
        //    // 检查TextureType是否为Sprite
        //    return importer.textureType == TextureImporterType.Sprite;
        //}
        return false;
    }
}