Augment SerializableDictionary to allow temporary duplicates in Editor

* Also fixes an issue with the "Init Controllers" type lookup within
  InteractionModeManager.css to find XRBaseControllers.

org.mixedrealitytoolkit.core/Utilities/SerializableDictionary.cs

@@ -21,23 +21,78 @@ public class SerializableDictionary<TKey, TValue> : Dictionary<TKey, TValue>, IS
 
         void ISerializationCallbackReceiver.OnBeforeSerialize()
         {
+#if !UNITY_EDITOR
             entries.Clear();
 
             foreach (KeyValuePair<TKey, TValue> pair in this)
             {
                 entries.Add(new SerializableDictionaryEntry(pair.Key, pair.Value));
             }
+#else
+            // While in Editor, the serialized entries list is managed differently and is not necessarily a 1:1 representation of
+            // the dictionary.  This allows for temporary duplicate keys, something the dictionary cannot do, while modifications
+            // are being made in the Inspector since the default behavior is to duplicate the last entry when adding a new one.
+
+            // Override the first entry that has a matching key from the dictionary, otherwise add to entries.
+            foreach (KeyValuePair<TKey, TValue> pair in this)
+            {
+                if (TryFindSerializableIndex(pair.Key, out int index))
+                {
+                    entries[index] = new SerializableDictionaryEntry(pair.Key, pair.Value);
+                }
+                else
+                {
+                    entries.Add(new SerializableDictionaryEntry(pair.Key, pair.Value));
+                }
+            }
+#endif
         }
 
         void ISerializationCallbackReceiver.OnAfterDeserialize()
         {
-            this.Clear();
+            base.Clear();
 
             foreach (SerializableDictionaryEntry entry in entries)
             {
-                this.Add(entry.Key, entry.Value);
+                base.TryAdd(entry.Key, entry.Value);
+            }
+        }
+
+#if UNITY_EDITOR
+        public new void Clear()
+        {
+            entries.Clear();
+            base.Clear();
+        }
+
+        public new bool Remove(TKey key, out TValue value)
+        {
+            if (base.Remove(key, out value))
+            {
+                if (TryFindSerializableIndex(key, out int index))
+                {
+                    entries.RemoveAt(index);
+                }
+
+                return true;
             }
+
+            return false;
+        }
+
+        public new bool Remove(TKey key)
+        {
+            return Remove(key, out _);
+        }
+
+        private bool TryFindSerializableIndex(TKey key, out int index)
+        {
+            var keyComparer = EqualityComparer<TKey>.Default;
+
+            index = entries.FindIndex((entry) => keyComparer.Equals(entry.Key, key));
+            return index != -1;
         }
+#endif
 
         [Serializable]
         private struct SerializableDictionaryEntry

org.mixedrealitytoolkit.input/Editor/Inspectors/InteractionModeManagerEditor.cs

@@ -2,6 +2,7 @@
 // Licensed under the BSD 3-Clause
 
 using MixedReality.Toolkit.Editor;
+using System.Collections.Generic;
 using UnityEditor;
 using UnityEngine;
 
@@ -27,6 +28,17 @@ public override void OnInspectorGUI()
             InteractionModeManager interactionModeManager = (InteractionModeManager)target;
 
             // Raise lots of errors if the interaction mode manager is configured incorrectly
+            var duplicateControllerMappings = GetDuplicateControllerMappings();
+            if (duplicateControllerMappings.Count > 0)
+            {
+                var duplicatedNameString = interactionModeManager.CompileDuplicatedNames(duplicateControllerMappings);
+
+                InspectorUIUtility.DrawError($"Duplicate controller mapping keys detected in the interaction mode manager on {interactionModeManager.gameObject.name}. " +
+                                    $"Please check the following controller mappings: {duplicatedNameString}");
+
+                GUI.color = InspectorUIUtility.ErrorColor;
+            }
+
             var duplicatedNames = interactionModeManager.GetDuplicateInteractionModes();
             if (duplicatedNames.Count > 0)
             {
@@ -58,5 +70,41 @@ public override void OnInspectorGUI()
 
             serializedObject.ApplyModifiedProperties();
         }
+
+        private HashSet<string> GetDuplicateControllerMappings()
+        {
+            HashSet<string> duplicatedNames = new HashSet<string>();
+
+            SerializedProperty controllerMapping = serializedObject.FindProperty("controllerMapping");
+            SerializedProperty entries = controllerMapping?.FindPropertyRelative("entries");
+
+            if (entries != null && entries.arraySize > 0)
+            {
+                HashSet<int> seenInstanceIDs = new HashSet<int>();
+
+                for (int i = 0; i < entries.arraySize; ++i)
+                {
+                    SerializedProperty entry = entries.GetArrayElementAtIndex(i);
+                    SerializedProperty key = entry.FindPropertyRelative("key");
+
+                    int instanceID = key != null && key.objectReferenceValue != null ?
+                        key.objectReferenceValue.GetInstanceID() : 0;
+
+                    if (seenInstanceIDs.Contains(instanceID))
+                    {
+                        string duplicateName = key != null && key.objectReferenceValue != null ?
+                            key.objectReferenceValue.name : "None (Game Object)";
+
+                        duplicatedNames.Add(duplicateName);
+                    }
+                    else
+                    {
+                        seenInstanceIDs.Add(instanceID);
+                    }
+                }
+            }
+
+            return duplicatedNames;
+        }
     }
 }

org.mixedrealitytoolkit.input/InteractionModes/InteractionModeManager.cs

@@ -71,7 +71,7 @@ public static InteractionModeManager Instance
         public void InitializeControllers()
         {
             controllerMapping.Clear();
-            foreach (XRController xrController in FindObjectUtility.FindObjectsByType<XRController>())
+            foreach (XRBaseController xrController in FindObjectUtility.FindObjectsByType<XRBaseController>())
             {
                 if (!controllerMapping.ContainsKey(xrController.gameObject))
                 {