c#里string和Json转换

[DataContract]
public class TextMessage
{
    [DataMember(Name = "content")]
    public string Content { get; set; }
}

[DataContract]
public class CustomerMessage
{
    [DataMember(Name = "touser")]
    public string touser { get; set; }

    [DataMember(Name = "msgtype")]
    public string msgtype { get; set; }

    [DataMember(Name = "text")]
    public TextMessage textMsg { get; set; }
}

CustomerMessage message = new CustomerMessage()
{
    touser = OpenIDBox.Text,
    msgtype = "text",
    textMsg = new TextMessage()
    {
        Content = ContentBox.Text
    }
};

DataContractJsonSerializer json = new DataContractJsonSerializer(message.GetType());
string szJson = "";

//序列化
using (MemoryStream stream = new MemoryStream())
{
    json.WriteObject(stream, message);
    szJson = Encoding.UTF8.GetString(stream.ToArray());
}

Console.WriteLine(szJson);

retStr = "<Json String>";
using (MemoryStream ms = new MemoryStream(Encoding.UTF8.GetBytes(retStr)))
{
    DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof(CustomerMessage));
    CustomerMessage_message = (CustomerMessage)serializer.ReadObject(ms);
}