截至撰写本文时，
NumberHandling property仅在.NET 5.0和.NET 6.0 RC中可用，而我无法使用它。不幸的是，itminus的字符串转数字转换器对我也没有起作用。
因此，我制作了另一个解决方案，处理不同的数字类型及其可空变体。我尽量使代码尽可能DRY。
数字和可空数字类型
首先，是用于字符串转数字和字符串转可空数字转换的主要通用类：
public delegate T FromStringFunc<T>(string str);
public delegate T ReadingFunc<T>(ref Utf8JsonReader reader);
public delegate void WritingAction<T>(Utf8JsonWriter writer, T value);
public class StringToNumberConverter<T> : JsonConverter<T> where T : struct
{
protected ISet<TypeCode> AllowedTypeCodes { get; }
protected FromStringFunc<T> FromString { get; }
protected ReadingFunc<T> ReadValue { get; }
protected WritingAction<T> WriteValue { get; }
public StringToNumberConverter(ISet<TypeCode> allowedTypeCodes, FromStringFunc<T> fromString, ReadingFunc<T> read, WritingAction<T> write)
: base()
{
AllowedTypeCodes = allowedTypeCodes;
FromString = fromString;
ReadValue = read;
WriteValue = write;
}
public override bool CanConvert(Type typeToConvert)
{
return AllowedTypeCodes.Contains(Type.GetTypeCode(typeToConvert));
}
public override T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
if (reader.TokenType == JsonTokenType.String)
{
var s = reader.GetString();
return FromString(s);
}
if (reader.TokenType == JsonTokenType.Number)
return ReadValue(ref reader);
using JsonDocument document = JsonDocument.ParseValue(ref reader);
throw new Exception($"unable to parse {document.RootElement} to number");
}
public override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions options)
{
WriteValue(writer, value);
}
}
public class StringToNullableNumberConverter<T> : JsonConverter<T?> where T : struct
{
private readonly StringToNumberConverter<T> stringToNumber;
protected WritingAction<T> WriteValue { get; }
public StringToNullableNumberConverter(ISet<TypeCode> allowedTypeCodes, FromStringFunc<T> fromString, ReadingFunc<T> read, WritingAction<T> write)
: base()
{
stringToNumber = new StringToNumberConverter<T>(allowedTypeCodes, fromString, read, write);
WriteValue = write;
}
public override bool CanConvert(Type typeToConvert)
{
return stringToNumber.CanConvert(Nullable.GetUnderlyingType(typeToConvert) ?? typeToConvert);
}
public override T? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
if (reader.TokenType == JsonTokenType.Null)
return null;
return stringToNumber.Read(ref reader, typeToConvert, options);
}
public override void Write(Utf8JsonWriter writer, T? value, JsonSerializerOptions options)
{
if (!value.HasValue)
writer.WriteNullValue();
else
stringToNumber.Write(writer, value.Value, options);
}
}
接下来是一个简化使用的工具类。它包含非通用的、类型精确的转换方法和设置：
static class StringToNumberUtil
{
public static readonly ISet<TypeCode> intCodes = new HashSet<TypeCode> { TypeCode.Byte, TypeCode.Int16, TypeCode.Int32 };
public static readonly ISet<TypeCode> longCodes = new HashSet<TypeCode> { TypeCode.Int64 };
public static readonly ISet<TypeCode> decimalCodes = new HashSet<TypeCode> { TypeCode.Decimal };
public static readonly ISet<TypeCode> doubleCodes = new HashSet<TypeCode> { TypeCode.Double };
public static int ParseInt(string s) => int.Parse(s, CultureInfo.InvariantCulture);
public static long ParseLong(string s) => long.Parse(s, CultureInfo.InvariantCulture);
public static decimal ParseDecimal(string s) => decimal.Parse(s, CultureInfo.InvariantCulture);
public static double ParseDouble(string s) => double.Parse(s, CultureInfo.InvariantCulture);
public static int ReadInt(ref Utf8JsonReader reader) => reader.GetInt32();
public static long ReadLong(ref Utf8JsonReader reader) => reader.GetInt64();
public static decimal ReadDecimal(ref Utf8JsonReader reader) => reader.GetDecimal();
public static double ReadDouble(ref Utf8JsonReader reader) => reader.GetDouble();
public static void WriteInt(Utf8JsonWriter writer, int value) => writer.WriteStringValue(value.ToString(CultureInfo.InvariantCulture));
public static void WriteLong(Utf8JsonWriter writer, long value) => writer.WriteStringValue(value.ToString(CultureInfo.InvariantCulture));
public static void WriteDecimal(Utf8JsonWriter writer, decimal value) => writer.WriteStringValue(value.ToString(CultureInfo.InvariantCulture));
public static void WriteDouble(Utf8JsonWriter writer, double value) => writer.WriteStringValue(value.ToString(CultureInfo.InvariantCulture));
}
最后，你可以为各个数字类型定义便捷类...
public class StringToIntConverter : StringToNumberConverter<int>
{
public StringToIntConverter()
: base(StringToNumberUtil.intCodes, StringToNumberUtil.ParseInt, StringToNumberUtil.ReadInt, StringToNumberUtil.WriteInt)
{
}
}
public class StringToNullableIntConverter : StringToNullableNumberConverter<int>
{
public StringToNullableIntConverter()
: base(StringToNumberUtil.intCodes, StringToNumberUtil.ParseInt, StringToNumberUtil.ReadInt, StringToNumberUtil.WriteInt)
{
}
}
... 并将它们注册到 JsonSerializerOptions 中，就像这样：
var options = new JsonSerializerOptions {
...
};
options.Converters.Add(new StringToIntConverter());
options.Converters.Add(new StringToNullableIntConverter());
...
（如果您喜欢的话）或者直接注册转换器。
options.Converters.Add(new StringToNumberConverter<int>(StringToNumberUtil.intCodes, StringToNumberUtil.ParseInt, StringToNumberUtil.ReadInt, StringToNumberUtil.WriteInt));
options.Converters.Add(new StringToNullableNumberConverter<int>(StringToNumberUtil.intCodes, StringToNumberUtil.ParseInt, StringToNumberUtil.ReadInt, StringToNumberUtil.WriteInt));
应反序列化为枚举的数字
如果您的 JSON 包含字符串编码的数字属性，其值具有可表示为枚举的预定义含义，则可以添加此内容。
public class StringToIntEnumConverter<T> : JsonConverter<T> where T : struct, System.Enum
{
private StringToIntConverter stringToInt = new StringToIntConverter();
public override bool CanConvert(Type typeToConvert)
{
return typeToConvert == typeof(T);
}
public override T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
int val = stringToInt.Read(ref reader, typeToConvert, options);
string underlyingValue = val.ToString(CultureInfo.InvariantCulture);
return (T)Enum.Parse(typeof(T), underlyingValue);
}
public override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions options)
{
var number = Convert.ChangeType(value, Enum.GetUnderlyingType(typeof(T)), CultureInfo.InvariantCulture);
writer.WriteStringValue(number.ToString());
}
}
public class StringToNullableIntEnumConverter<T> : JsonConverter<T?> where T : struct, System.Enum
{
private StringToIntEnumConverter<T> stringToIntEnum = new StringToIntEnumConverter<T>();
public override bool CanConvert(Type typeToConvert)
{
return stringToIntEnum.CanConvert(Nullable.GetUnderlyingType(typeToConvert) ?? typeToConvert);
}
public override T? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
if (reader.TokenType == JsonTokenType.Null)
return null;
return stringToIntEnum.Read(ref reader, typeToConvert, options);
}
public override void Write(Utf8JsonWriter writer, T? value, JsonSerializerOptions options)
{
if (!value.HasValue)
{
writer.WriteNullValue();
return;
}
stringToIntEnum.Write(writer, value.Value, options);
}
}
在JsonSerializerOptions中的使用方法：
var options = new JsonSerializerOptions {
...
};
options.Converters.Add(new StringToIntEnumConverter<OrderFlags>());
options.Converters.Add(new StringToNullableIntEnumConverter<OrderFlags>());
...
System.InvalidCastException: Unable to cast object of type 'System.Collections.Generic.List1[System.String]' to type 'System.Collections.Generic.IList1[System.Object]'的异常。此外，您不需要覆盖 CanConvert() 方法。 - SlimShaggyint.TryParse(s, NumberStyles.Integer, NumberFormatInfo.InvariantInfo, out var i)和double.TryParse(s, NumberStyles.Float, NumberFormatInfo.InvariantInfo, out var d)。 - dbc