Fixing issue where the Object Manipulation example fails in Unity 2018.3

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;
-            }
-        }
     }
 }