包含对象的堆栈不适用于JsonConverter.ReadJson()，因此您无法在ReadJson() 中做您想做的事情。
相反，您可以创建一个custom contract resolver，它根据正在为其生成合同的对象的属性应用适当配置的StringSanitizingConverter 实例。
首先，假设您的数据模型、属性和JsonConverter 如下所示（我必须修改一些内容以使您的代码编译并包含一些额外的测试用例）：
public class Candidate
{
[StringSanitizingOptions(Option.ToLowerCase)]
public string CandidateName { get; set; }
[StringSanitizingOptions(Option.DoNotTrim)]
public string StringLiteral { get; set; }
public string DefaultString { get; set; }
public List<string> DefaultStrings { get; set; }
}
[System.AttributeUsage(System.AttributeTargets.Property | System.AttributeTargets.Field | System.AttributeTargets.Parameter, AllowMultiple = false, Inherited = true)]
public class StringSanitizingOptionsAttribute : System.Attribute
{
public Option StringSanitizeOptions { get; set; }
public StringSanitizingOptionsAttribute(Option stringSanitizeOptions)
{
this.StringSanitizeOptions = stringSanitizeOptions;
}
}
[Flags]
public enum Option
{
Default = 0,
ToLowerCase = (1<<0),
DoNotTrim = (1<<1),
}
public static class StringSanitizeOptionsExtensions
{
public static bool HasFlag(this Option options, Option flag)
{
return (options & flag) == flag;
}
}
public class StringSanitizingConverter : JsonConverter
{
readonly Option options;
public StringSanitizingConverter() : this(Option.Default) { }
public StringSanitizingConverter(Option options)
{
this.options = options;
}
public override bool CanConvert(Type objectType)
{
return objectType == typeof(string);
}
public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
if (reader.TokenType == JsonToken.String)
if (reader.Value != null)
{
var sanitizedString = (reader.Value as string);
if (!options.HasFlag(Option.DoNotTrim))
sanitizedString = sanitizedString.Trim();
if (options.HasFlag(Option.ToLowerCase))
sanitizedString = sanitizedString.ToLowerInvariant();
return sanitizedString;
}
return reader.Value;
}
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
// WriteJson is never called with null
var text = (string)value;
if (!options.HasFlag(Option.DoNotTrim))
text = text.Trim();
writer.WriteValue(text);
}
}
接下来，从How to add metadata to describe which properties are dates in JSON.Net中获取ConfigurableContractResolver，并定义扩展方法JsonContractExtensions.AddStringConverters()：
public static class JsonContractExtensions
{
public static JsonContract AddStringConverters(this JsonContract contract)
{
if (contract is JsonPrimitiveContract)
{
if (contract.UnderlyingType == typeof(string))
contract.Converter = new StringSanitizingConverter();
}
else if (contract is JsonObjectContract)
{
var objectContract = (JsonObjectContract)contract;
foreach (var property in objectContract.Properties)
{
if (property.PropertyType == typeof(string))
{
var attr = property.AttributeProvider.GetAttributes(typeof(StringSanitizingOptionsAttribute), true)
.Cast<StringSanitizingOptionsAttribute>()
.SingleOrDefault();
if (attr != null)
{
property.Converter = property.MemberConverter = new StringSanitizingConverter(attr.StringSanitizeOptions);
}
}
}
}
return contract;
}
}
public class ConfigurableContractResolver : DefaultContractResolver
{
// This contract resolver taken from the answer to
// https://stackoverflow.com/questions/46047308/how-to-add-metadata-to-describe-which-properties-are-dates-in-json-net
// https://stackoverflow.com/a/46083201/3744182
readonly object contractCreatedPadlock = new object();
event EventHandler<ContractCreatedEventArgs> contractCreated;
int contractCount = 0;
void OnContractCreated(JsonContract contract, Type objectType)
{
EventHandler<ContractCreatedEventArgs> created;
lock (contractCreatedPadlock)
{
contractCount++;
created = contractCreated;
}
if (created != null)
{
created(this, new ContractCreatedEventArgs(contract, objectType));
}
}
public event EventHandler<ContractCreatedEventArgs> ContractCreated
{
add
{
lock (contractCreatedPadlock)
{
if (contractCount > 0)
{
throw new InvalidOperationException("ContractCreated events cannot be added after the first contract is generated.");
}
contractCreated += value;
}
}
remove
{
lock (contractCreatedPadlock)
{
if (contractCount > 0)
{
throw new InvalidOperationException("ContractCreated events cannot be removed after the first contract is generated.");
}
contractCreated -= value;
}
}
}
protected override JsonContract CreateContract(Type objectType)
{
var contract = base.CreateContract(objectType);
OnContractCreated(contract, objectType);
return contract;
}
}
public class ContractCreatedEventArgs : EventArgs
{
public JsonContract Contract { get; private set; }
public Type ObjectType { get; private set; }
public ContractCreatedEventArgs(JsonContract contract, Type objectType)
{
this.Contract = contract;
this.ObjectType = objectType;
}
}
public static class ConfigurableContractResolverExtensions
{
public static ConfigurableContractResolver Configure(this ConfigurableContractResolver resolver, EventHandler<ContractCreatedEventArgs> handler)
{
if (resolver == null || handler == null)
throw new ArgumentNullException();
resolver.ContractCreated += handler;
return resolver;
}
}
那么，终于可以反序列化和序列化Candidate，如下：
var settings = new JsonSerializerSettings
{
ContractResolver = new ConfigurableContractResolver
{
}.Configure((s, e) => { e.Contract.AddStringConverters(); }),
};
var candidate = JsonConvert.DeserializeObject<Candidate>(json, settings);
var json2 = JsonConvert.SerializeObject(candidate, Formatting.Indented, settings);
注意事项：
-
我不知道为什么包含对象的堆栈在 ReadJson() 中不可用。可能性包括：
- 简单。
-
JSON 对象是“一组无序的名称/值对”，因此不能保证在读取属性值时尝试访问包含的 .Net 对象，因为可能尚未读取所需的信息还没有（甚至可能还没有构建父级）。
由于StringSanitizingConverter 的默认实例应用于为string 本身生成的合约，因此无需将转换器添加到JsonSerializer.SettingsConverters。这反过来可能会导致小的性能提升，因为CanConvert 将不再被调用。
JsonProperty.MemberConverter 最近在 Json.NET 11.0.1 中被标记为过时，但在 Json.NET 的早期版本中必须设置为与 JsonProperty.Converter 相同的值。如果您使用的是 11.0.1 或更新的版本，您应该可以删除该设置。
您可能需要cache the contract resolver 以获得最佳性能。
要修改 asp.net-web-api 中的 JsonSerializerSettings，请参阅 JsonSerializerSettings and Asp.Net Core、Web API: Configure JSON serializer settings on action or controller level、How to set custom JsonSerializerSettings for Json.NET in MVC 4 Web API? 或ASP.NET Core API JSON serializersettings per request，具体取决于您的要求和使用的框架版本。
示例工作 .Net fiddle here.