Silverlight启用wcf服务引用参数不起作用

Question

我有这个网络服务：

namespace SUS.Web.Services
{
[ServiceContract(Namespace = "")]   
[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
public class PublicServices:BaseService
{
    public PublicServices()
        : base(false)
    { }

    [OperationContract]
    public ObservableCollection<VmSolution> GetSolutions()
    {

        SusConfigurationSection solutionCofigurationsSection = (SusConfigurationSection)System.Configuration.ConfigurationManager.GetSection("SolutionConfigurations");
        return solutionCofigurationsSection.GetVmSolutions();
    }

    [OperationContract]
    public string Authenticate(ref VmLogin vmLogin)
    {           
        vmLogin.ErrorMessage = "test message";          
        return "";
    }
}

}

问题在于，当我从Silverlight调用Authenticate方法时，ErrorMessage属性包含字符串“test message”，但此值不会传播到传递的clientVmLogin对象。

public partial class LoginPage : UserControl
{
    VmLogin clientVmLogin = new VmLogin();


    PublicServicesClient proxyPublic; 
    public LoginPage()
    {
        DevExpress.Xpf.Core.ThemeManager.ApplicationTheme = DevExpress.Xpf.Core.Theme.Office2007Blue;
        InitializeComponent();

        proxyPublic = new PublicServicesClient();
        proxyPublic.Endpoint.Address = new EndpointAddress(WebServiceHelper.GetWebserviceFolderAddress() + "PublicServices.svc");
        proxyPublic.InnerChannel.OperationTimeout = WebServiceHelper.GetTimeOut();
        proxyPublic.AuthenticateCompleted += new EventHandler<AuthenticateCompletedEventArgs>(proxyPublic_AuthenticateCompleted);
        proxyPublic.GetSolutionsCompleted += new EventHandler<GetSolutionsCompletedEventArgs>(proxyPublic_GetSolutionsCompleted);

        this.DataContext = clientVmLogin;

        clientVmLogin.LoginNeeded+=new EventHandler(login_LoginNeeded);
        Loaded += new RoutedEventHandler(LoginPage_Loaded);
    }

    void proxyPublic_poslinuggetCompleted(object sender, poslinuggetCompletedEventArgs e)
    {
        int i = 0;
    }

    void login_LoginNeeded(object sender, EventArgs e)
    {
        proxyPublic.AuthenticateAsync(this.clientVmLogin);      
    }


    void proxyPublic_AuthenticateCompleted(object sender, AuthenticateCompletedEventArgs e)
    {

        if (this.clientVmLogin.ErrorMessage != e.vmLogin.ErrorMessage)
        {
            // i have problem. Ref is not working at all.
        }

    }

你知道吗，请问哪里有问题？我是唯一一个将使用我的wcf服务的人，因此我希望使用ref参数传递自动更新客户端对象。

非常感谢你。

汤姆