asp.net-mvc-4 – ASP.Net Web Api在POST上不绑定模型

这是我的模型：

[DataContract]
public class RegisterDataModel
{
    [DataMember(IsRequired = true)]
    public String SiteKey { get; set; }

    [DataMember(IsRequired = true)]
    public String UserId { get; set; }

    [DataMember(IsRequired = true)]
    public String UserName { get; set; }
}

这是我的Web Api操作：

public class RegisterController : ApiController
    {
    public Guid Post([ModelBinder] RegisterDataModel registerDataModel)
    {
        if (!ModelState.IsValid)
        {
            throw new ModelStateApiException(ModelState);
        }
        var userProfileDataContract = userProfileBusinessLibrary.GetNewOne();
        userProfileDataContract.UserId = registerDataModel.UserId;
        userProfileDataContract.UserName = registerDataModel.UserName;

        var userKey = userProfileBusinessLibrary.Register(registerDataModel.SiteKey,userProfileDataContract);

        return userKey;
    }
    }

在添加[ModelBinder]之前,registerDataModel为null.添加[ModelBinder]后,registerDataModel是一个RegisterDataModel实例,但所有属性值都为空.

这是我通过Fiddler的请求：

http://local.testwebsite.com/api/register

Request Headers:
User-Agent: Fiddler
Host: local.testwebsite.com
Content-Length: 89
Content-Type: application/json; charset=utf-8:

Request Body:
{ 
 "SiteKey":"qwerty","UserId": "12345qwerty","UserName":"john q"
}

我发现我的帖子数据绑定到RegisterDataModel属性是什么？谢谢你的帮助.