// this method corrects the IDs for photonviews in the scene and in prefabs
    // make sure prefabs always use viewID 0
    // make sure instances never use a owner
    // this is a editor class that should only run if not playing
    internal static void HierarchyChange()
    {
        if (Application.isPlaying)
        {
            //Debug.Log("HierarchyChange ignored, while running.");
            CheckSceneForStuckHandlers = true;  // done once AFTER play mode.
            return;
        }

        if (CheckSceneForStuckHandlers)
        {
            CheckSceneForStuckHandlers = false;
            PhotonNetworkManager.InternalCleanPhotonMonoFromSceneIfStuck();
        }

        HashSet <PhotonView> pvInstances             = new HashSet <PhotonView>();
        HashSet <int>        usedInstanceViewNumbers = new HashSet <int>();
        bool fixedSomeId = false;

        //// the following code would be an option if we only checked scene objects (but we can check all PVs)
        //PhotonView[] pvObjects = GameObject.FindSceneObjectsOfType(typeof(PhotonView)) as PhotonView[];
        //Debug.Log("HierarchyChange. PV Count: " + pvObjects.Length);

        string levelName = SceneManagerHelper.ActiveSceneName;

        #if UNITY_EDITOR
        levelName = SceneManagerHelper.EditorActiveSceneName;
        #endif
        int minViewIdInThisScene = PunSceneSettings.MinViewIdForScene(levelName);
        //Debug.Log("Level '" + Application.loadedLevelName + "' has a minimum ViewId of: " + minViewIdInThisScene);

        PhotonView[] pvObjects = Resources.FindObjectsOfTypeAll(typeof(PhotonView)) as PhotonView[];

        foreach (PhotonView view in pvObjects)
        {
            // first pass: fix prefabs to viewID 0 if they got a view number assigned (cause they should not have one!)
            if (EditorUtility.IsPersistent(view.gameObject))
            {
                if (view.viewID != 0 || view.prefixBackup != -1 || view.instantiationId != -1)
                {
                    Debug.LogWarning("PhotonView on persistent object being fixed (id and prefix must be 0). Was: " + view);
                    view.viewID          = 0;
                    view.prefixBackup    = -1;
                    view.instantiationId = -1;
                    EditorUtility.SetDirty(view);   // even in Unity 5.3+ it's OK to SetDirty() for non-scene objects.
                    fixedSomeId = true;
                }
            }
            else
            {
                // keep all scene-instanced PVs for later re-check
                pvInstances.Add(view);
            }
        }

        Dictionary <GameObject, int> idPerObject = new Dictionary <GameObject, int>();

        // second pass: check all used-in-scene viewIDs for duplicate viewIDs (only checking anything non-prefab)
        // scene-PVs must have user == 0 (scene/room) and a subId != 0
        foreach (PhotonView view in pvInstances)
        {
            if (view.ownerId > 0)
            {
                Debug.Log("Re-Setting Owner ID of: " + view);
            }
            view.ownerId = 0;   // simply make sure no owner is set (cause room always uses 0)
            view.prefix  = -1;  // TODO: prefix could be settable via inspector per scene?!

            if (view.viewID != 0)
            {
                if (view.viewID < minViewIdInThisScene || usedInstanceViewNumbers.Contains(view.viewID))
                {
                    view.viewID = 0; // avoid duplicates and negative values by assigning 0 as (temporary) number to be fixed in next pass
                }
                else
                {
                    usedInstanceViewNumbers.Add(view.viewID); // builds a list of currently used viewIDs

                    int instId = 0;
                    if (idPerObject.TryGetValue(view.gameObject, out instId))
                    {
                        view.instantiationId = instId;
                    }
                    else
                    {
                        view.instantiationId         = view.viewID;
                        idPerObject[view.gameObject] = view.instantiationId;
                    }
                }
            }
        }

        // third pass: anything that's now 0 must get a new (not yet used) ID (starting at 0)
        int lastUsedId = (minViewIdInThisScene > 0) ? minViewIdInThisScene - 1 : 0;

        foreach (PhotonView view in pvInstances)
        {
            if (view.viewID == 0)
            {
                Undo.RecordObject(view, "Automatic viewID change for: " + view.gameObject.name);

                // Debug.LogWarning("setting scene ID: " + view.gameObject.name + " ID: " + view.subId.ID + " scene ID: " + view.GetSceneID() + " IsPersistent: " + EditorUtility.IsPersistent(view.gameObject) + " IsSceneViewIDFree: " + IsSceneViewIDFree(view.subId.ID, view));
                int nextViewId = PhotonViewHandler.GetID(lastUsedId, usedInstanceViewNumbers);

                view.viewID = nextViewId;

                int instId = 0;
                if (idPerObject.TryGetValue(view.gameObject, out instId))
                {
                    view.instantiationId = instId;
                }
                else
                {
                    view.instantiationId         = view.viewID;
                    idPerObject[view.gameObject] = nextViewId;
                }

                lastUsedId  = nextViewId;
                fixedSomeId = true;

                #if !UNITY_MIN_5_3
                EditorUtility.SetDirty(view);
                #endif
            }
        }


        if (fixedSomeId)
        {
            //Debug.LogWarning("Some subId was adjusted."); // this log is only interesting for Exit Games
        }
    }