Imported Upstream version 4.0.0~alpha1

Former-commit-id: 806294f5ded97629b74c85c09952f2a74fe182d9

external/referencesource/System.Web/ModelBinding/KeyValuePairModelBinderProvider.cs

@@ -0,0 +1,22 @@
+namespace System.Web.ModelBinding {
+    using System.Collections.Generic;
+
+    public sealed class KeyValuePairModelBinderProvider : ModelBinderProvider {
+
+        public override IModelBinder GetBinder(ModelBindingExecutionContext modelBindingExecutionContext, ModelBindingContext bindingContext) {
+            ModelBinderUtil.ValidateBindingContext(bindingContext);
+
+            string keyFieldName = ModelBinderUtil.CreatePropertyModelName(bindingContext.ModelName, "key");
+            string valueFieldName = ModelBinderUtil.CreatePropertyModelName(bindingContext.ModelName, "value");
+
+            if (bindingContext.UnvalidatedValueProvider.ContainsPrefix(keyFieldName) && bindingContext.UnvalidatedValueProvider.ContainsPrefix(valueFieldName)) {
+                return ModelBinderUtil.GetPossibleBinderInstance(bindingContext.ModelType, typeof(KeyValuePair<,>) /* supported model type */, typeof(KeyValuePairModelBinder<,>) /* binder type */);
+            }
+            else {
+                // 'key' or 'value' missing
+                return null;
+            }
+        }
+
+    }
+}