英文:
CastException when serializing derived class with System.Text.Json
问题
我有一个简单的CLI应用程序，根据args获取不同的数据，然后使用System.Text.Json进行JSON序列化。
我遇到的问题是，在序列化派生类（例如，在这种情况下是List<DerivedImage>）时，如何使用基类的自定义转换器（例如ImageConverter）来解决这个问题？
public static int Main(string[] args)
{
object data = "images ls" switch
{
"images ls" => new List<DerivedImage>() { new DerivedImage() },
// ... 其他情况 ...
};
var options = new JsonSerializerOptions()
{
Converters = { new ImageConverter() }
};
var stringified = JsonSerializer.Serialize(data, options);
// ^ 这里出错了！
// 异常消息：
// System.InvalidCastException: 无法将类型为 'ImageConverter'
// 的对象强制转换为类型 'JsonConverter[DerivedImage]'
return 1;
}
public class ImageConverter : JsonConverter<Image>
{
public override bool CanConvert(Type typeToConvert)
{
return typeof(Image).IsAssignableFrom(typeToConvert);
}
public override Image Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
throw new NotImplementedException();
}
public override void Write(Utf8JsonWriter writer, Image value, JsonSerializerOptions options)
{
// 从不会执行到这里。
}
}
public abstract class Image { }
public class DerivedImage : Image { }
在上面的代码片段中，如何让序列化器在传递data时使用ImageConverter呢？
英文:
I've got a simple CLI app that gets some different data depending on args and then JSON serializes it using System.Text.Json.
The problem I'm running into is when serializing a derived class (ie. List<DerivedImage> in this case) with a custom converter for the base class (ie. ImageConverter).
public static int Main(string[] args)
{
object data = "images ls" switch
{
"images ls" => new List<DerivedImage>() { new DerivedImage() },
// ... etc ...
};
var options = new JsonSerializerOptions()
{
Converters = { new ImageConverter() }
};
var stringified = JsonSerializer.Serialize(data, options);
// ^ THIS ERRORS!
// Exception message:
// System.InvalidCastException: 'Unable to cast object of type 'ImageConverter'
// to type 'JsonConverter[DerivedImage]'
return 1;
}
public class ImageConverter : JsonConverter<Image>
{
public override bool CanConvert(Type typeToConvert)
{
return typeof(Image).IsAssignableFrom(typeToConvert);
}
public override Image Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
throw new NotImplementedException();
}
public override void Write(Utf8JsonWriter writer, Image value, JsonSerializerOptions options)
{
// It never gets here.
}
}
public abstract class Image { }
public class DerivedImage : Image { }
With the snippet above, how can I get the serializer to use the ImageConverter when passed data?
答案1
得分: 0
升级项目配置中的 TargetFramework 从 .net6 到 .net7 已解决。
英文:
Resolved by upgrading TargetFramework in the project config from .net6 to .net7.
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