Imported Upstream version 3.6.0

Former-commit-id: da6be194a6b1221998fc28233f2503bd61dd9d14

external/aspnetwebstack/src/System.Web.Mvc/ModelMetadataProviders.cs

@@ -0,0 +1,31 @@
+// Copyright (c) Microsoft Corporation. All rights reserved. See License.txt in the project root for license information.
+
+namespace System.Web.Mvc
+{
+    public class ModelMetadataProviders
+    {
+        private static ModelMetadataProviders _instance = new ModelMetadataProviders();
+        private ModelMetadataProvider _currentProvider;
+        private IResolver<ModelMetadataProvider> _resolver;
+
+        internal ModelMetadataProviders(IResolver<ModelMetadataProvider> resolver = null)
+        {
+            _resolver = resolver ?? new SingleServiceResolver<ModelMetadataProvider>(
+                                        () => _currentProvider,
+                                        new CachedDataAnnotationsModelMetadataProvider(),
+                                        "ModelMetadataProviders.Current");
+        }
+
+        public static ModelMetadataProvider Current
+        {
+            get { return _instance.CurrentInternal; }
+            set { _instance.CurrentInternal = value; }
+        }
+
+        internal ModelMetadataProvider CurrentInternal
+        {
+            get { return _resolver.Current; }
+            set { _currentProvider = value ?? new EmptyModelMetadataProvider(); }
+        }
+    }
+}