.net 在mvvmLight viewmodel中使用WebContext时出现问题

和往常一样，我尝试使用一种新技术，但一开始就遇到了问题

我有一个Silverlight业务应用程序+MvvmLight

在我的viewmodel中，我尝试获取登录用户的角色：

    public HomeViewModel()
    {
        if (IsInDesignMode)
        {
            // Code runs in Blend --> create design time data.
        }
        else
        {
            // Code runs "for real"                
            DetermineStartableProcesses();
        }
    }

    private void DetermineStartableProcesses()
    {
        _startableProcesses = new ObservableCollection<WorkflowProcess>(
            WebContext.Current.User.Roles.SelectMany(r =>
                WorkflowProcess.GetStartableByRole(r))
                .Distinct());
    }

看起来ViewModelLocator在创建webcontext get之前正在应用程序启动时实例化ViewModels，这意味着在viewmodel构造函数中执行大量工作对我来说是个坏主意

---

那么，我应该在viewmodel中的什么位置检索将被数据绑定的数据呢？

这就是我在使用mvvm light时避免这种情况的方法。因此，WebContext首先被创建

在App.xaml中：

 <Application.ApplicationLifetimeObjects>
        <ct:WebContext>
            <ct:WebContext.Authentication>
                <as:FormsAuthentication DomainContextType="MyProj.Data.AuthenticationContext, MyProj.Client.Common, Version=1.0.0." />
            </ct:WebContext.Authentication>
        </ct:WebContext>
    </Application.ApplicationLifetimeObjects>
    <Application.Resources>
        <ResourceDictionary>

            <ct:ViewModelLocator x:Key="Locator"
                                 d:IsDataSource="True" />
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="Assets/Styles.xaml" />
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>

---

在应用程序构造函数中实例化WebContext。然后在调用之前，将其添加到App_启动中的资源中

public App()
        {
            Startup += Application_Startup;
            Exit += Application_Exit;
            UnhandledException += Application_UnhandledException;

            if (IsInDesignModeStatic)
            {
                Services.ServiceLoader.LoadDesignTimeServices();
                DispatcherHelper.Initialize();
            }
            else
            {
                try
                {

                    ServiceLoader.LoadRunTimeServices();
                    DispatcherHelper.Initialize();

                    WebContext webContext = new WebContext();
                    ApplicationLifetimeObjects.Add(WebContext.Current);

                    FormsAuthentication fa = new FormsAuthentication();
                    fa.DomainContext = new Web.Services.AuthenticationDomainContext();
                    WebContext.Current.Authentication = fa;
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.ToString());
                }
            }

            InitializeComponent();
        }



private void Application_Startup(object sender, StartupEventArgs e)
        {
            this.Resources.Add("WebContext", WebContext.Current);

            RootVisual = new MainPage();

        }

由于我的自定义AuthenticationDomainContext和Membershipprovider，我发现在代码隐藏中执行这一部分更容易…但是Dereks也很好，我只是在使用代码隐藏，而我正在让一切正常工作

public App()
        {
            Startup += Application_Startup;
            Exit += Application_Exit;
            UnhandledException += Application_UnhandledException;

            if (IsInDesignModeStatic)
            {
                Services.ServiceLoader.LoadDesignTimeServices();
                DispatcherHelper.Initialize();
            }
            else
            {
                try
                {

                    ServiceLoader.LoadRunTimeServices();
                    DispatcherHelper.Initialize();

                    WebContext webContext = new WebContext();
                    ApplicationLifetimeObjects.Add(WebContext.Current);

                    FormsAuthentication fa = new FormsAuthentication();
                    fa.DomainContext = new Web.Services.AuthenticationDomainContext();
                    WebContext.Current.Authentication = fa;
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.ToString());
                }
            }

            InitializeComponent();
        }



private void Application_Startup(object sender, StartupEventArgs e)
        {
            this.Resources.Add("WebContext", WebContext.Current);

            RootVisual = new MainPage();

        }