验证用户时关闭登录对话框？

Question

Pretty new at MVVM, so excuse the clumsiness of my code...

My program (App.xaml.cs) starts out by opening the main window (MainView)

        protected override void OnStartup(StartupEventArgs e)
    {            
        Window window = new MainView();
        window.DataContext = new MainViewModel();
        window.WindowStyle = WindowStyle.None;
        window.ResizeMode = ResizeMode.NoResize;
        window.Show();

        base.OnStartup(e);
    }

and the constructor of MainView starts out by opening the login dialog (LoginView)

        public MainView()
    {
        var login = new LoginView();
        login.DataContext = new LoginViewModel();
        DataContext = new MainViewModel();
        login.ShowDialog();
        InitializeComponent();
    }

In my LoginViewModel (this is probably the wrong place for it, but I'll be refactoring to be more MVVM compliant later on) I verify the password

            if (user.PasswordHash == newHash)
        {
            MyGlobals.userLoggedIn = user.UserName;
            ShowMessageBox("Hurra.");
        }

and when that's done I want to close the dialog, which would leave me with the MainView again - I've tried just about everything I can think of, but... my inexperience is definitely holding me back.

Any ideas on how I can approach this? Google hasn't been that much of a help so far...

Answer 1

The MVVM purest way of closing a View from its ViewModel is via an attached property.

public static class perWindowHelper
{
    public static readonly DependencyProperty CloseWindowProperty = DependencyProperty.RegisterAttached(
        "CloseWindow",
        typeof(bool?),
        typeof(perWindowHelper),
        new PropertyMetadata(null, OnCloseWindowChanged));

    private static void OnCloseWindowChanged(DependencyObject target, DependencyPropertyChangedEventArgs args)
    {
        if (!(target is Window view))
        {
            return;
        }

        if (view.IsModal())
        {
            view.DialogResult = args.NewValue as bool?;
        }
        else
        {
            view.Close();
        }
    }

    public static void SetCloseWindow(Window target, bool? value)
    {
        target.SetValue(CloseWindowProperty, value);
    }

    public static bool IsModal(this Window window)
    {
        var fieldInfo = typeof(Window).GetField("_showingAsDialog", BindingFlags.Instance | BindingFlags.NonPublic);
        return fieldInfo != null && (bool)fieldInfo.GetValue(window);
    }
}

Usage is

<Window x:Class= ...
    vhelp:perWindowHelper.CloseWindow="{Binding ViewClosed}">

which is bound to a corresponding bool? property on your ViewModel, that you set to true when you want to close the View.

More details on my blog post .

Answer 2

You can use a NuGet package called MvvmDialogs for all dialog related operations. The one capable of opening modal dialogs is called ShowDialog . You can see an example of it here .