C# 序列化时不忽略DefaultValue中声明的数组
我使用JSON作为配置文件,我想为数组设置一个默认值。我希望序列化的JSON忽略数组,如果它等于C# 序列化时不忽略DefaultValue中声明的数组,c#,json.net,C#,Json.net,我使用JSON作为配置文件,我想为数组设置一个默认值。我希望序列化的JSON忽略数组,如果它等于DefaultValueAttribute,那么如果我在程序的第二个版本中决定更改DefaultValues,那么将加载新的默认值,而不是原始默认值的未触及副本 我的问题是,如果数组引用没有更改,但程序中的其他代码正在更改数组,但保留数组中的值,那么代码就可以工作。(该程序维护该类的许多克隆,因此无法避免) 下面是使用c#interactive显示的问题: using System.Component
DefaultValueAttribute
,那么如果我在程序的第二个版本中决定更改DefaultValues,那么将加载新的默认值,而不是原始默认值的未触及副本
我的问题是,如果数组引用没有更改,但程序中的其他代码正在更改数组,但保留数组中的值,那么代码就可以工作。(该程序维护该类的许多克隆,因此无法避免)
下面是使用c#interactive显示的问题:
using System.ComponentModel;
using Newtonsoft.Json;
class A
{
[DefaultValue(new int[] { 4, 6, 12 })]
public int[] SomeArray;
}
var serializerSettings = new JsonSerializerSettings
{
DefaultValueHandling = DefaultValueHandling.IgnoreAndPopulate,
};
var a = new A();
JsonConvert.PopulateObject("{}", a, serializerSettings);
Console.WriteLine(JsonConvert.SerializeObject(a, serializerSettings));
// Prints {}
a.SomeArray = new int[] { 4, 6, 12 };
Console.WriteLine(JsonConvert.SerializeObject(a, serializerSettings));
// Prints {"SomeArray":[4,6,12]}
如您所见,第一个Serialized对象可以工作,但是如果数组内容相同但不是相同的数组引用,它会将默认值写入json,这是我想要避免的
在这种情况下,我有没有办法让Json.net忽略阵列?除了您确定的问题之外,您当前的体系结构还存在一些其他问题:
DefaultValueAttribute
:
ADefaultValueAttribute
不会导致成员自动初始化为该属性的值。您必须在代码中设置初始值。
A
的所有实例共享对int[3]{4,6,12}
数组的单个全局实例的引用。由于数组不是真正的只读,这意味着修改A
的一个实例将使用默认值修改A
的所有其他当前和未来的实例:
var serializerSettings = new JsonSerializerSettings
{
DefaultValueHandling = DefaultValueHandling.IgnoreAndPopulate,
};
var a1 = JsonConvert.DeserializeObject<A>("{}", serializerSettings);
// The following succeeds
Assert.IsTrue(a1.SomeArray.SequenceEqual(new int[] { 4, 6, 12 }));
// Sime SomeArray is a globally shared pointer, this will modify all current and future instances of A!
a1.SomeArray[0] = -999;
var a2 = JsonConvert.DeserializeObject<A>("{}", serializerSettings);
// The following now fails!
Assert.IsTrue(a2.SomeArray.SequenceEqual(new int[] { 4, 6, 12 }));
演示小提琴#1
如果决定对数组使用DefaultValueHandling
和DefaultValueAttribute
,则需要:
并在序列化时将其用作:
var serializerSettings = new JsonSerializerSettings
{
DefaultValueHandling = DefaultValueHandling.IgnoreAndPopulate,
ContractResolver = resolver,
};
var a = new A();
JsonConvert.PopulateObject("{}", a, serializerSettings);
Console.WriteLine(JsonConvert.SerializeObject(a, serializerSettings));
Assert.IsTrue(JsonConvert.SerializeObject(a, serializerSettings) == "{}");
a.SomeArray = new int[] { 4, 6, 12 };
Console.WriteLine(JsonConvert.SerializeObject(a, serializerSettings));
Assert.IsTrue(JsonConvert.SerializeObject(a, serializerSettings) == "{}");
演示小提琴2
注:
- 契约解析器仅对秩1的数组实现。如果需要,您可以将其扩展到多维数组
- 契约解析器在将默认值数组实例设置为成员时自动克隆该实例,以避免上述问题2。如果不需要,可以删除
ArrayDefaultValueProvider
- 目前还不清楚Json.NET的预期功能是否支持数组值默认值
public class ArrayDefaultValueContractResolver : DefaultContractResolver
{
class ArrayDefaultValueProvider : IValueProvider
{
readonly IValueProvider baseProvider;
readonly System.Array defaultValue;
public ArrayDefaultValueProvider(IValueProvider baseProvider, System.Array defaultValue)
{
this.baseProvider = baseProvider;
this.defaultValue = defaultValue;
}
#region IValueProvider Members
public object GetValue(object target)
{
return baseProvider.GetValue(target);
}
public void SetValue(object target, object value)
{
// Make sure the default value is cloned since arrays are not truly read only.
if (value != null && object.ReferenceEquals(value, defaultValue))
value = defaultValue.Clone();
baseProvider.SetValue(target, value);
}
#endregion
}
static void AddArrayDefaultHandling<T>(JsonProperty property)
{
var defaultValue = (T [])property.DefaultValue;
// If the default value has length > 0, clone it when setting it back into the object.
if (defaultValue.Length > 0)
{
property.ValueProvider = new ArrayDefaultValueProvider(property.ValueProvider, defaultValue);
}
// Add a ShouldSerialize method that checks for memberwise array equality.
var valueProvider = property.ValueProvider;
var oldShouldSerialize = property.ShouldSerialize;
Predicate<object> shouldSerialize = target =>
{
var array = (T[])valueProvider.GetValue(target);
return !(array == null || array.SequenceEqual(defaultValue));
};
if (oldShouldSerialize == null)
property.ShouldSerialize = shouldSerialize;
else
property.ShouldSerialize = (target) => shouldSerialize(target) && oldShouldSerialize(target);
}
protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
{
var property = base.CreateProperty(member, memberSerialization);
if (property.PropertyType.IsArray && property.DefaultValue != null && property.DefaultValue.GetType() == property.PropertyType
&& property.PropertyType.GetArrayRank() == 1)
{
typeof(ArrayDefaultValueContractResolver)
.GetMethod("AddArrayDefaultHandling", BindingFlags.Static | BindingFlags.NonPublic)
.MakeGenericMethod(property.PropertyType.GetElementType())
.Invoke(null, BindingFlags.Static | BindingFlags.NonPublic, null, new [] { property }, null);
}
return property;
}
}
static IContractResolver resolver = new ArrayDefaultValueContractResolver();
var serializerSettings = new JsonSerializerSettings
{
DefaultValueHandling = DefaultValueHandling.IgnoreAndPopulate,
ContractResolver = resolver,
};
var a = new A();
JsonConvert.PopulateObject("{}", a, serializerSettings);
Console.WriteLine(JsonConvert.SerializeObject(a, serializerSettings));
Assert.IsTrue(JsonConvert.SerializeObject(a, serializerSettings) == "{}");
a.SomeArray = new int[] { 4, 6, 12 };
Console.WriteLine(JsonConvert.SerializeObject(a, serializerSettings));
Assert.IsTrue(JsonConvert.SerializeObject(a, serializerSettings) == "{}");