Fixing issue where the Object Manipulation example fails in Unity 201…

…8.3 due to the order of calls to OnEnable and OnAwake (1) being different than previous versions of the editor and (2) exposing an initialization bug in ManipulationSystem.cs. This commit refactors ManipulationSystem.cs to allow access to static member ManipulationSystem.Instance before any calls to non-static member Awake.

Assets/GoogleARCore/Examples/ObjectManipulation/Scripts/ManipulationSystem.cs

@@ -34,6 +34,16 @@ public class ManipulationSystem : MonoBehaviour
     {
         private static ManipulationSystem s_Instance = null;
 
+        private DragGestureRecognizer m_DragGestureRecognizer = new DragGestureRecognizer();
+
+        private PinchGestureRecognizer m_PinchGestureRecognizer = new PinchGestureRecognizer();
+
+        private TwoFingerDragGestureRecognizer m_TwoFingerDragGestureRecognizer = new TwoFingerDragGestureRecognizer();
+
+        private TapGestureRecognizer m_TapGestureRecognizer = new TapGestureRecognizer();
+
+        private TwistGestureRecognizer m_TwistGestureRecognizer = new TwistGestureRecognizer();
+
         /// <summary>
         /// Gets the ManipulationSystem instance.
         /// </summary>
@@ -43,7 +53,15 @@ public static ManipulationSystem Instance
             {
                 if (s_Instance == null)
                 {
-                    Debug.LogError("No instance of ManipulationSystem exists in the scene.");
+                    var manipulationSystems = FindObjectsOfType<ManipulationSystem>();
+                    if (manipulationSystems.Length > 0)
+                    {
+                        s_Instance = manipulationSystems[0];
+                    }
+                    else
+                    {
+                        Debug.LogError("No instance of ManipulationSystem exists in the scene.");
+                    }
                 }
 
                 return s_Instance;
@@ -53,27 +71,57 @@ public static ManipulationSystem Instance
         /// <summary>
         /// Gets the Drag gesture recognizer.
         /// </summary>
-        public DragGestureRecognizer DragGestureRecognizer { get; private set; }
+        public DragGestureRecognizer DragGestureRecognizer
+        {
+            get
+            {
+                return m_DragGestureRecognizer;
+            }
+        }
 
         /// <summary>
         /// Gets the Pinch gesture recognizer.
         /// </summary>
-        public PinchGestureRecognizer PinchGestureRecognizer { get; private set; }
+        public PinchGestureRecognizer PinchGestureRecognizer
+        {
+            get
+            {
+                return m_PinchGestureRecognizer;
+            }
+        }
 
         /// <summary>
         /// Gets the two finger drag gesture recognizer.
         /// </summary>
-        public TwoFingerDragGestureRecognizer TwoFingerDragGestureRecognizer { get; private set; }
+        public TwoFingerDragGestureRecognizer TwoFingerDragGestureRecognizer
+        {
+            get
+            {
+                return m_TwoFingerDragGestureRecognizer;
+            }
+        }
 
         /// <summary>
         /// Gets the Tap gesture recognizer.
         /// </summary>
-        public TapGestureRecognizer TapGestureRecognizer { get; private set; }
+        public TapGestureRecognizer TapGestureRecognizer
+        {
+            get
+            {
+                return m_TapGestureRecognizer;
+            }
+        }
 
         /// <summary>
         /// Gets the Twist gesture recognizer.
         /// </summary>
-        public TwistGestureRecognizer TwistGestureRecognizer { get; private set; }
+        public TwistGestureRecognizer TwistGestureRecognizer
+        {
+            get
+            {
+                return m_TwistGestureRecognizer;
+            }
+        }
 
         /// <summary>
         /// Gets the current selected object.
@@ -85,12 +133,16 @@ public static ManipulationSystem Instance
         /// </summary>
         public void Awake()
         {
-            _InitializeSingleton();
-            DragGestureRecognizer = new DragGestureRecognizer();
-            PinchGestureRecognizer = new PinchGestureRecognizer();
-            TwoFingerDragGestureRecognizer = new TwoFingerDragGestureRecognizer();
-            TapGestureRecognizer = new TapGestureRecognizer();
-            TwistGestureRecognizer = new TwistGestureRecognizer();
+            if (Instance != this)
+            {
+                Debug.LogWarning("Multiple instances of ManipulationSystem detected in the scene." +
+                                 " Only one instance can exist at a time. The duplicate instances" +
+                                 " will be destroyed.");
+                DestroyImmediate(gameObject);
+                return;
+            }
+
+            DontDestroyOnLoad(gameObject);
         }
 
         /// <summary>
@@ -116,7 +168,7 @@ internal void Deselect()
         /// <summary>
         /// Select an object.
         /// </summary>
-        /// <param name="target">The object to select.</param> 
+        /// <param name="target">The object to select.</param>
         internal void Select(GameObject target)
         {
             if (SelectedObject == target)
@@ -127,22 +179,5 @@ internal void Select(GameObject target)
             Deselect();
             SelectedObject = target;
         }
-
-        private void _InitializeSingleton()
-        {
-            if (s_Instance == null)
-            {
-                s_Instance = this;
-                DontDestroyOnLoad(gameObject);
-            }
-            else if (Instance != this)
-            {
-                Debug.LogWarning("Multiple instances of ManipulationSystem detected in the scene." +
-                                 " Only one instance can exist at a time. The duplicate instances" +
-                                 " will be destroyed.");
-                DestroyImmediate(gameObject);
-                return;
-            }
-        }
     }
 }