Csharp 如果属性名为xyz，我需要使用System.Text.Json修改字符串类型的值""<>

从.NET 8或.NET 9 Preview 2开始，无法获得父属性名或JsonConverter<T>.Read()内部的序列化路径的任何其他部分，因为它不为Utf8JsonReader所知. 如需确认，请参见this answer至105. 正如您所看到的，当调用Read()时，读取器已经前进到属性名之外.

相反，在.NET 7 and later中，您可以使用typeInfo modifier以编程方式将转换器应用于名为xyz的任何属性.要执行此操作，请首先创建以下修改器和转换器:

public static partial class JsonExtensions
{
    public static Action<JsonTypeInfo> AddPropertyConverter(JsonConverter converter, string name) => typeInfo =>
    {
        // Use StringComparison.OrdinalIgnoreCase if you want to apply the comparer to properties named Xyz and XYZ also.
        foreach (var property in typeInfo.Properties.Where(p => converter.CanConvert(p.PropertyType)
                                                           && String.Equals(p.GetMemberName(), name, StringComparison.Ordinal)))
        {
            // If you only want to apply the converter only when there is not one already, use ??=
            // property.CustomConverter ??= CustomJsonConverter.Instance;
            property.CustomConverter = CustomJsonConverter.Instance;
        }
    };

    public static string? GetMemberName(this JsonPropertyInfo property) => (property.AttributeProvider as MemberInfo)?.Name;
}

public class CustomJsonConverter : JsonConverter<string?>
{
    public static CustomJsonConverter Instance { get; } = new(); // Cache a single instance for performance

    public override bool HandleNull => false; // Change to true if you want to modify null string values.

    public override string? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) =>
        "Modified: " + reader.GetString();

    public override void Write(Utf8JsonWriter writer, string? value, JsonSerializerOptions options) => 
        // Write the value as a string
        writer.WriteStringValue(value);
}

然后在. NET 8和更高版本中，使用WithAddedModifier()将修饰符应用到您想要的IJsonTypeInfoResolver:

string propertyName = "xyz";

JsonSerializerOptions _options = new()
{
    // Configure either a DefaultJsonTypeInfoResolver or some JsonSerializerContext and add the required modifier:
    TypeInfoResolver = new DefaultJsonTypeInfoResolver()
        .WithAddedModifier(JsonExtensions.AddPropertyConverter(CustomJsonConverter.Instance, propertyName)),
    // Add other options as required
    DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
    PropertyNameCaseInsensitive = true,             
};

或者在. NET 7中直接创建并配置DefaultJsonTypeInfoResolver，如下所示:

string propertyName = "xyz";

JsonSerializerOptions _options = new()
{
    TypeInfoResolver = new DefaultJsonTypeInfoResolver()
    {
        Modifiers = {JsonExtensions.AddPropertyConverter(CustomJsonConverter.Instance, propertyName)}
    },
    // Add other options as required
    DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
    PropertyNameCaseInsensitive = true,             
};

现在，在反序列化过程中，您的转换器将根据需要重新映射类型为string的所有名为xyz的属性的值，而无需向序列化类添加属性或以其他方式修改这些属性.

请注意，如果希望重映射值为null的属性，则必须重写HandleNull并返回true.

.NET8here和.NET7here的演示小提琴.