Fix setting extension data with existing key (#1878)

Src/Newtonsoft.Json.Tests/Issues/Issue1874.cs

@@ -0,0 +1,67 @@
+#region License
+// Copyright (c) 2007 James Newton-King
+//
+// Permission is hereby granted, free of charge, to any person
+// obtaining a copy of this software and associated documentation
+// files (the "Software"), to deal in the Software without
+// restriction, including without limitation the rights to use,
+// copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following
+// conditions:
+//
+// The above copyright notice and this permission notice shall be
+// included in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+// OTHER DEALINGS IN THE SOFTWARE.
+#endregion
+
+using Newtonsoft.Json.Linq;
+using Newtonsoft.Json.Linq.JsonPath;
+using System;
+using System.Collections.Generic;
+#if DNXCORE50
+using Xunit;
+using Test = Xunit.FactAttribute;
+using Assert = Newtonsoft.Json.Tests.XUnitAssert;
+#else
+using NUnit.Framework;
+#endif
+
+namespace Newtonsoft.Json.Tests.Issues
+{
+    [TestFixture]
+    public class Issue1874
+    {
+        [Test]
+        public void Test()
+        {
+            var something = new Something();
+
+            JsonConvert.PopulateObject(@"{""Foo"": 1, ""Bar"": 2}", something);
+
+            Assert.AreEqual(1, something.Extra.Count);
+            Assert.AreEqual(2, (int)something.Extra["Bar"]);
+
+            JsonConvert.PopulateObject(@"{""Foo"": 2, ""Bar"": 3}", something);
+
+            Assert.AreEqual(1, something.Extra.Count);
+            Assert.AreEqual(3, (int)something.Extra["Bar"]);
+        }
+
+        public class Something
+        {
+            public int Foo { get; set; }
+
+            [JsonExtensionData]
+            public IDictionary<string, JToken> Extra { get; set; }
+        }
+    }
+}

Src/Newtonsoft.Json/Serialization/DefaultContractResolver.cs

@@ -496,15 +496,15 @@ namespace Newtonsoft.Json.Serialization
                  ? JsonTypeReflector.ReflectionDelegateFactory.CreateSet<object>(member)
                  : null;
                 Func<object> createExtensionDataDictionary = JsonTypeReflector.ReflectionDelegateFactory.CreateDefaultConstructor<object>(createdType);
-                MethodInfo addMethod = t.GetMethod("Add", new[] { keyType, valueType });
-                if (addMethod == null)
+                MethodInfo setMethod = t.GetProperty("Item", BindingFlags.Public | BindingFlags.Instance, null, valueType, new[] { keyType }, null)?.GetSetMethod();
+                if (setMethod == null)
                 {
-                    // Add is explicitly implemented and non-public
+                    // Item is explicitly implemented and non-public
                     // get from dictionary interface
-                    addMethod = dictionaryType.GetMethod("Add", new[] {keyType, valueType});
+                    setMethod = dictionaryType.GetProperty("Item", BindingFlags.Public | BindingFlags.Instance, null, valueType, new[] { keyType }, null)?.GetSetMethod();
                 }
 
-                MethodCall<object, object> setExtensionDataDictionaryValue = JsonTypeReflector.ReflectionDelegateFactory.CreateMethodCall<object>(addMethod);
+                MethodCall<object, object> setExtensionDataDictionaryValue = JsonTypeReflector.ReflectionDelegateFactory.CreateMethodCall<object>(setMethod);
 
                 ExtensionDataSetter extensionDataSetter = (o, key, value) =>
                 {