EditorManager.cs

using UnityEngine;
using UnityEditor;
using UnityEditor.SceneManagement;

/// <summary>
/// Controls things that happen in the editor at every tick or when scene changes.
/// Fix for crash when hitting run or unloading scene if a child is activeInHierarchy but some parent is !activeSelf.
/// Issue #828408
/// https://issuetracker.unity3d.com/issues/active-child-of-disabled-parent-crashes-editor-when-creating-new-scene
/// </summary>
///
[InitializeOnLoad]
public class EditorManager {
    private static double lastUpdateTime = -1;
    private static float updateFrequencySeconds = 60f;
    private static System.DateTime startTime = System.DateTime.UtcNow;
    private static string currentScene;

    /// <summary>
    /// Runs on Unity editor start, on compile, and on play in editor.
    /// </summary>
    static EditorManager() {
        // fix after scene changes (crash still occurs when leaving buggy scene)
        EditorApplication.hierarchyWindowChanged += HierarchyWindowChanged;

        // and when hitting play before crash would occur
        EditorApplication.playmodeStateChanged += FixInvalidActiveChildren;

        // and once a minute for good measure
        EditorApplication.update += Update;
    }

    /// <summary>
    /// Runs every frame while in edit mode and in play mode while in editor.
    /// Runs more often and reliably than Update on MonoBehaviors with [ExecuteInEditMode]
    /// </summary>
    static void Update() {
        if (!isUnityEditMode) return;

        // perform check every minute
        double currentTime = (System.DateTime.UtcNow - startTime).TotalSeconds;
        if (currentTime > lastUpdateTime + updateFrequencySeconds) {
            lastUpdateTime = currentTime;
            FixInvalidActiveChildren();
        }
    }

    /// <summary>
    /// When object created, renamed, moved or destroyed in scene hierarchy,
    /// including when scene changes and on compile.
    /// </summary>
    static void HierarchyWindowChanged() {
        if (!isUnityEditMode) return;

        // scene changed
        if (currentScene != EditorSceneManager.GetActiveScene().path) {
            currentScene = EditorSceneManager.GetActiveScene().path;
            FixInvalidActiveChildren();
        }
    }

    /// <summary>
    /// Runs once a minute while in edit mode.
    /// </summary>
    static void FixInvalidActiveChildren() {
        GameObject[] parents = UnityEngine.SceneManagement.SceneManager.GetActiveScene().GetRootGameObjects();
        foreach (GameObject parent in parents) {
            GameObject invalidActiveChild = FindInvalidActiveChild(parent, !parent.activeSelf);
            if (invalidActiveChild != null) {
                Debug.LogWarning("EditorBugFixer found invalid active child, fixing... " + invalidActiveChild.GetPath());
                // twiddle root parent activeSelf to force child to become !activeInHierarchy
                bool parentWasActive = parent.activeSelf;
                parent.SetActive(false);
                parent.SetActive(true);
                parent.SetActive(false);
                parent.SetActive(parentWasActive);
            }
        }
    }

    static GameObject FindInvalidActiveChild(GameObject parent, bool someParentInactive) {
        foreach (Transform child in parent.transform) {
            if (someParentInactive && child.gameObject.activeInHierarchy) {
                // only need one per root, twiddling root should fix any others
                return child.gameObject;
            } else {
                bool someInactive = someParentInactive || !child.gameObject.activeSelf;
                GameObject invalidGrandchild = FindInvalidActiveChild(child.gameObject, someInactive);
                if (invalidGrandchild != null) {
                    return invalidGrandchild;
                }
            }
        }
        return null;
    }

    /// <summary>
    /// Are we in the editor and not playing?
    /// </summary>
    public static bool isUnityEditMode {
        get {
#if UNITY_EDITOR
        if (!UnityEditor.EditorApplication.isPlaying) return true;
#endif
        return false;
        }
    }
}