JsonPropertyAttribute忽略派生类中的私有属性

在序列化具有私有属性的派生对象时，我遇到了Json.Net的问题。 好吧

public class Base { [JsonProperty] private string Type { get { return "Base"; } } } public class Inherited : Base { [JsonProperty] private string Type { get { return "Inherited"; } } } 

当我序列化Inherited实例时， Type属性始终设置为“Base”。 我发现工作的唯一方法是属性受保护或公共，并在子类中重写。

为什么这样工作？ 那是一个错误吗？

Answer 1

看起来这是Json.NET的预期行为。 来自ReflectionUtils.cs ：

  private static void GetChildPrivateProperties(IList initialProperties, Type targetType, BindingFlags bindingAttr) { // fix weirdness with private PropertyInfos only being returned for the current Type // find base type properties and add them to result // also find base properties that have been hidden by subtype properties with the same name while ((targetType = targetType.BaseType()) != null) { foreach (PropertyInfo propertyInfo in targetType.GetProperties(bindingAttr)) { PropertyInfo subTypeProperty = propertyInfo; if (!IsPublic(subTypeProperty)) { // have to test on name rather than reference because instances are different // depending on the type that GetProperties was called on int index = initialProperties.IndexOf(p => p.Name == subTypeProperty.Name); if (index == -1) { initialProperties.Add(subTypeProperty); } else { PropertyInfo childProperty = initialProperties[index]; // don't replace public child with private base if (!IsPublic(childProperty)) { // replace nonpublic properties for a child, but gotten from // the parent with the one from the child // the property gotten from the child will have access to private getter/setter initialProperties[index] = subTypeProperty; } 

这是生成类型的属性列表的位置，正如您所看到的，有些代码有意将基类中具有相同名称的属性添加到inheritance的类中。

我不知道为什么Json.NET这样做，你可能想报告一个问题并问为什么。 在此期间，您可以使用IContractResolver有选择地阻止此行为：

 [System.AttributeUsage(AttributeTargets.Property)] public class JsonPreferDerivedPropertyAttribute : System.Attribute { } public class PreferDerivedPropertyContractResolver : DefaultContractResolver { static PropertyInfo GetDerivedPropertyRecursive(Type objectType, Type stopType, PropertyInfo property) { var parameters = property.GetIndexParameters().Select(info => info.ParameterType).ToArray(); for (; objectType != null && objectType != stopType; objectType = objectType.BaseType) { var derivedProperty = objectType.GetProperty( property.Name, BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic, null, property.PropertyType, parameters, null); if (derivedProperty == null) continue; if (derivedProperty == property) return derivedProperty; // No override. if (derivedProperty.GetCustomAttribute() != null) return derivedProperty; } return null; } protected override List GetSerializableMembers(Type objectType) { var list = base.GetSerializableMembers(objectType); for (int i = 0; i < list.Count; i++) { var property = list[i] as PropertyInfo; if (property == null) continue; if (property.DeclaringType != objectType) { var derivedProperty = GetDerivedPropertyRecursive(objectType, property.DeclaringType, property); if (derivedProperty == null || derivedProperty == property) continue; if (derivedProperty != property && (property.GetGetMethod(true) == null || derivedProperty.GetGetMethod(true) != null) && (property.GetSetMethod(true) == null || derivedProperty.GetSetMethod(true) != null)) { list[i] = derivedProperty; } } } return list; } } 

我建议有选择地这样做，因为我不完全理解为什么Json.NET会做它的function。 上面的代码仅覆盖应用了自定义JsonPreferDerivedPropertyAttribute属性的派生类属性的默认行为。

然后使用它像：

 public class Base { [JsonProperty] private string Type { get { return "Base"; } } } public class Inherited : Base { [JsonProperty] [JsonPreferDerivedPropertyAttribute] private string Type { get { return "Inherited"; } } } public class VeryInherited : Inherited { [JsonProperty] public string VeryInheritedProperty { get { return "VeryInherited"; } } } public static class TestOverride { public static void Test() { var inherited = new Inherited(); var json1 = JsonConvert.SerializeObject(inherited, Formatting.Indented, new JsonSerializerSettings() { ContractResolver = new PreferDerivedPropertyContractResolver() }); var veryInherited = new VeryInherited(); var json2 = JsonConvert.SerializeObject(veryInherited, Formatting.Indented, new JsonSerializerSettings() { ContractResolver = new PreferDerivedPropertyContractResolver() }); Debug.WriteLine(json1); Debug.WriteLine(json2); } } 

产出是：

 { "Type": "Inherited" } 

和

 { "VeryInheritedProperty": "VeryInherited", "Type": "Inherited" }