NGUI5.6与Unity2018.3 PrefabMode冲突

情景：

Unity在升级到2018.3版本后 新增了Prefab Mode系统，可以通过Open Prefab直接打开新的Scene对预设进行编辑。

NGUI的UI控件需要依附于UIRoot节点作为其顶级父节点，UIRoot主要是控制UI控件的变化和缩放。

问题：

Unity的Prefab Mode强制在对Prefab节点进行删除/移动时 需要在Prefab Mode系统中才能进行，因此若是在NGUI5.6升级Unity到2018.3 就会出现 在Scene场景中无法删、移预设，但是进入Prefab Mode会有导致NGUI控件报错的问题。

解决方法：

1，简单的解决方法是 每次进行预设编辑时 使用Unpack 进行预设的解引用，这样不需要进入Prefab Mode也可以进行预设的删、移，而缺点就是 每次修改之后需要进行预设的覆盖，带来操作成本，隐患则是进行Unpack会导致引用丢失，需要每次都重新拖引用，提高了操作失误率。

2，对NGUI 5.6 源码修改，在进入Prefab Mode时为其创建UIRoot，在寻找解决方案的时候发现了NGUI2018已经有相应的解决方法，这里将需要修改的代码整理出来：

1,实现配置环境

UIRect.cs 
`protected virtual void Awake () {  `
`#if UNITY_2018_3_OR_NEWER `
`    NGUITools.CheckForPrefabStage (gameObject);  `
`#endif `

`    mStarted = false; `
`    mGo = gameObject; `
`    mTrans = transform; `
`} `
`static public void CheckForPrefabStage (GameObject gameObject) {  `
`#if UNITY_EDITOR && UNITY_2018_3_OR_NEWER `
`    var prefabStage = UnityEditor.Experimental.SceneManagement.PrefabStageUtility.GetPrefabStage (gameObject); `
`    if (prefabStage == null) `
`        return; `

`    var rootsInParents = gameObject.GetComponentsInParent<UIRoot> (true); `
`    var panelsInParents = gameObject.GetComponentsInParent<UIPanel> (true); `

`    bool missingRoot = rootsInParents.Length == 0; `
`    bool missingPanel = panelsInParents.Length == 0; `

`    if (!missingRoot && !missingPanel) `
`        return; `

`    // Since this function is called from Awake/OnEnable, utilities like PrefabStage.prefabContentsRoot `
`    // or Scene.GetRootGameObjects () aren't available at this point `

`    var instanceRoot = gameObject.transform; `
`    while (instanceRoot.parent != null) `
`        instanceRoot = instanceRoot.parent; `

`    GameObject container = UnityEditor.EditorUtility.CreateGameObjectWithHideFlags ("UIRoot (Environment)", HideFlags.DontSave); `
`    container.layer = instanceRoot.gameObject.layer; `

`    if (missingRoot) `
`        container.AddComponent<UIRoot> (); `

`    if (missingPanel) `
`        container.AddComponent<UIPanel> (); `

`    UnityEngine.SceneManagement.SceneManager.MoveGameObjectToScene (container, prefabStage.scene); `
`    instanceRoot.SetParent (container.transform, false); `
`#endif `
`} `

2，实现在预设场景能够正确保存NGUI预设

NGUITools.cs 
`static public void SetDirty (UnityEngine.Object obj) `
`{  `
`#if UNITY_EDITOR `
`    if (obj) `
`    {  `
`        if (UnityEditor.AssetDatabase.Contains(obj)) `
`        {  `
`            UnityEditor.EditorUtility.SetDirty(obj); `
`         } `
`        else if (!Application.isPlaying) `
`        {  `
`            if (obj is Component) `
`            {  `
`                var component = (Component)obj; `
`                UnityEditor.SceneManagement.EditorSceneManager.MarkSceneDirty(component.gameObject.scene); `
`             } `
`            else if (obj is UnityEditor.EditorWindow || obj is ScriptableObject) `
`            {  `
`                UnityEditor.EditorUtility.SetDirty(obj); `
`             } `
`            else `
`            {  `
`                UnityEditor.EditorUtility.SetDirty(obj); `
`                UnityEditor.SceneManagement.EditorSceneManager.MarkAllScenesDirty(); `
`             } `
`         } `
`     } `
`    //if (obj) `
`    //{  `
`    // //if (obj is Component) Debug.Log(NGUITools.GetHierarchy((obj as Component).gameObject), obj); `
`    // //else if (obj is GameObject) Debug.Log(NGUITools.GetHierarchy(obj as GameObject), obj); `
`    // //else Debug.Log("Hmm... " + obj.GetType(), obj); `
`    // UnityEditor.EditorUtility.SetDirty(obj); `
`    // } `
`#endif `
`} `

3，实现渲染

UIDrawCall 
`static UIDrawCall Create (string name, UIPanel pan, Material mat, Texture tex, Shader shader) `
`{  `
`    UIDrawCall dc = Create(name); `
`    dc.gameObject.layer = pan.cachedGameObject.layer; `
`    dc.baseMaterial = mat; `
`    dc.mainTexture = tex; `
`    dc.shader = shader; `
`    dc.renderQueue = pan.startingRenderQueue; `
`    dc.sortingOrder = pan.sortingOrder; `
`    dc.manager = pan; `

`#if UNITY_EDITOR && UNITY_2018_3_OR_NEWER `
`    // We need to perform this check here and not in Create (string) to get to manager reference `
`    var prefabStage = UnityEditor.Experimental.SceneManagement.PrefabStageUtility.GetCurrentPrefabStage (); `
`    if (prefabStage != null && dc.manager != null) `
`    {  `
`        // If prefab stage exists and new daw call `
`        var stage = UnityEditor.SceneManagement.StageUtility.GetStageHandle (dc.manager.gameObject); `
`        if (stage == prefabStage.stageHandle) `
`            UnityEngine.SceneManagement.SceneManager.MoveGameObjectToScene (dc.gameObject, prefabStage.scene); `
`} `
`#endif `
`    return dc; `
`} `