Fix compilation errors for Unity 2018

Author: arimger

Assets/Editor Toolbox/Editor/SceneView/ToolboxEditorSceneViewObjectSelector.cs

@@ -41,12 +41,16 @@ public static void Show(List<GameObject> gameObjects, Vector2 position)
 
         private void OnEnable()
         {
+#if UNITY_2019_1_OR_NEWER
             UnityEditor.SceneView.duringSceneGui += OnSceneViewGui;
+#endif
         }
 
         private void OnDisable()
         {
+#if UNITY_2019_1_OR_NEWER
             UnityEditor.SceneView.duringSceneGui -= OnSceneViewGui;
+#endif
             highlightedRenderers.Clear();
             highlightedObject = null;
         }
@@ -391,6 +395,7 @@ private void UpdateHighlightedRenderers()
             highlightedRenderers.AddRange(highlightedObject.GetComponentsInChildren<Renderer>(true));
         }
 
+#if UNITY_2019_1_OR_NEWER
         private void OnSceneViewGui(UnityEditor.SceneView sceneView)
         {
             if (highlightedRenderers.Count == 0 ||
@@ -418,6 +423,7 @@ private void OnSceneViewGui(UnityEditor.SceneView sceneView)
             }
 #endif
         }
+#endif
 
         private GameObject HighlightedObject
         {

Assets/Editor Toolbox/Editor/Utilities/PropertyUtility.cs

@@ -428,9 +428,11 @@ public static void OverrideLabelByValue(GUIContent label, SerializedProperty pro
                 case SerializedPropertyType.ObjectReference:
                     label.text = property.objectReferenceValue ? property.objectReferenceValue.ToString() : "null";
                     break;
+#if UNITY_2019_3_OR_NEWER
                 case SerializedPropertyType.ManagedReference:
                     label.text = property.managedReferenceValue?.ToString() ?? "null";
                     break;
+#endif
                 case SerializedPropertyType.LayerMask:
                     switch (property.intValue)
                     {