Json.Net 无法序列化为流，但可以正常序列化为字符串

在内部，JsonConvert.SerializeObject(obj, Formatting.Indented)归结为

JsonSerializer jsonSerializer = JsonSerializer.Create(null);
StringWriter stringWriter = new StringWriter(new StringBuilder(256), (IFormatProvider) CultureInfo.InvariantCulture);
using (JsonTextWriter jsonTextWriter = new JsonTextWriter((TextWriter) stringWriter))
{
  jsonTextWriter.Formatting = formatting;
  jsonSerializer.Serialize((JsonWriter) jsonTextWriter, value);
}
return stringWriter.ToString();

这很好用。但是，如果我执行以下操作：

string json;

JsonSerializer jsonSerializer = JsonSerializer.Create();

using (var stream = new MemoryStream())
using (var streamWriter = new StreamWriter(stream, Encoding.UTF8))
using (var jsonWriter = new JsonTextWriter(streamWriter))
{
    serializer.Serialize(jsonWriter, cmd);

    stream.Position = 0;
    using (var reader = new StreamReader(stream))
    {
        json = reader.ReadToEnd();
    }
}

那么值json is ""。谁能指出我的错误吗？

问题是你没有冲水streamWriter写完后：

serializer.Serialize(jsonWriter, cmd);
streamWriter.Flush();
stream.Position = 0;

或者，为什么不直接使用StringWriter首先？

using (var writer = new StringWriter())
{
    using (var jsonWriter = new JsonTextWriter(writer))
    {
        serializer.Serialize(jsonWriter, cmd);
        Console.WriteLine(writer.ToString());
    }
}