在学习(仍在学习)MVVM时，我真的为这个概念挣扎了一段时间。我的决定，以及我认为其他人已经决定但我不清楚的是:

我最初的想法是ViewModel不应该被允许直接调用对话框，因为它没有业务决定对话框应该如何显示。正因为如此，我开始思考如何像在MVP(即View.ShowSaveFileDialog())一样传递消息。然而，我认为这是错误的方法。

ViewModel直接调用对话框是可以的。然而，当您测试ViewModel时，这意味着对话框要么在测试期间弹出，要么全部失败(从未真正尝试过这个)。

因此，在测试时需要使用对话框的“测试”版本。这意味着，对于您拥有的任何对话，您都需要创建一个Interface，并模拟对话响应，或者创建一个具有默认行为的测试模拟。

您应该已经在使用某种服务定位器或IoC，您可以对其进行配置，以便根据上下文提供正确的版本。

使用这种方法，你的ViewModel仍然是可测试的，根据你如何模拟对话框，你可以控制行为。

希望这能有所帮助。

使用可冻结命令

<Grid>
        <Grid.DataContext>
            <WpfApplication1:ViewModel />
        </Grid.DataContext>


        <Button Content="Text">
            <Button.Command>
                <WpfApplication1:MessageBoxCommand YesCommand="{Binding MyViewModelCommand}" />
            </Button.Command>
        </Button>

</Grid>

public class MessageBoxCommand : Freezable, ICommand
{
    public static readonly DependencyProperty YesCommandProperty = DependencyProperty.Register(
        "YesCommand",
        typeof (ICommand),
        typeof (MessageBoxCommand),
        new FrameworkPropertyMetadata(null)
        );


    public static readonly DependencyProperty OKCommandProperty = DependencyProperty.Register(
        "OKCommand",
        typeof (ICommand),
        typeof (MessageBoxCommand),
        new FrameworkPropertyMetadata(null)
        );


    public static readonly DependencyProperty CancelCommandProperty = DependencyProperty.Register(
        "CancelCommand",
        typeof (ICommand),
        typeof (MessageBoxCommand),
        new FrameworkPropertyMetadata(null)
        );


    public static readonly DependencyProperty NoCommandProperty = DependencyProperty.Register(
        "NoCommand",
        typeof (ICommand),
        typeof (MessageBoxCommand),
        new FrameworkPropertyMetadata(null)
        );


    public static readonly DependencyProperty MessageProperty = DependencyProperty.Register(
        "Message",
        typeof (string),
        typeof (MessageBoxCommand),
        new FrameworkPropertyMetadata("")
        );

    public static readonly DependencyProperty MessageBoxButtonsProperty = DependencyProperty.Register(
        "MessageBoxButtons",
        typeof(MessageBoxButton),
        typeof(MessageBoxCommand),
        new FrameworkPropertyMetadata(MessageBoxButton.OKCancel)
        );

    public ICommand YesCommand
    {
        get { return (ICommand) GetValue(YesCommandProperty); }
        set { SetValue(YesCommandProperty, value); }
    }

    public ICommand OKCommand
    {
        get { return (ICommand) GetValue(OKCommandProperty); }
        set { SetValue(OKCommandProperty, value); }
    }

    public ICommand CancelCommand
    {
        get { return (ICommand) GetValue(CancelCommandProperty); }
        set { SetValue(CancelCommandProperty, value); }
    }

    public ICommand NoCommand
    {
        get { return (ICommand) GetValue(NoCommandProperty); }
        set { SetValue(NoCommandProperty, value); }
    }

    public MessageBoxButton MessageBoxButtons
    {
        get { return (MessageBoxButton)GetValue(MessageBoxButtonsProperty); }
        set { SetValue(MessageBoxButtonsProperty, value); }
    }

    public string Message
    {
        get { return (string) GetValue(MessageProperty); }
        set { SetValue(MessageProperty, value); }
    }

    public void Execute(object parameter)
    {
        var messageBoxResult = MessageBox.Show(Message);
        switch (messageBoxResult)
        {
            case MessageBoxResult.OK:
                OKCommand.Execute(null);
                break;
            case MessageBoxResult.Yes:
                YesCommand.Execute(null);
                break;
            case MessageBoxResult.No:
                NoCommand.Execute(null);
                break;
            case MessageBoxResult.Cancel:
                if (CancelCommand != null) CancelCommand.Execute(null); //Cancel usually means do nothing ,so can be null
                break;

        }
    }

    public bool CanExecute(object parameter)
    {
        return true;
    }

    public event EventHandler CanExecuteChanged;


    protected override Freezable CreateInstanceCore()
    {
        throw new NotImplementedException();
    }
}

我遇到了同样的情况，并将MessageBox包装成一个设计器不可见控件。详情在我的博客里

http://geekswithblogs.net/mukapu/archive/2010/03/12/user-prompts-messagebox-with-mvvm.aspx

同样可以扩展到任何模态对话框，文件浏览控件等。

标准方法

在花了几年时间在WPF中处理这个问题之后，我终于找到了在WPF中实现对话框的标准方法。以下是这种方法的优点:

清洁 不违反MVVM设计模式 ViewModal从不引用任何UI库(WindowBase, PresentationFramework等) 非常适合自动化测试 对话框可以很容易地被替换。

那么关键是什么呢?是DI + IoC。

下面是它的工作原理。我正在使用MVVM Light，但这种方法也可以扩展到其他框架:

Add a WPF Application project to your solution. Call it App. Add a ViewModal Class Library. Call it VM. App references VM project. VM project doesn't know anything about App. Add NuGet reference to MVVM Light to both projects. I'm using MVVM Light Standard these days, but you are okay with the full Framework version too. Add an interface IDialogService to VM project: public interface IDialogService { void ShowMessage(string msg, bool isError); bool AskBooleanQuestion(string msg); string AskStringQuestion(string msg, string default_value); string ShowOpen(string filter, string initDir = "", string title = ""); string ShowSave(string filter, string initDir = "", string title = "", string fileName = ""); string ShowFolder(string initDir = ""); bool ShowSettings(); } Expose a public static property of IDialogService type in your ViewModelLocator, but leave registration part for the View layer to perform. This is the key.: public static IDialogService DialogService => SimpleIoc.Default.GetInstance<IDialogService>(); Add an implementation of this interface in the App project. public class DialogPresenter : IDialogService { private static OpenFileDialog dlgOpen = new OpenFileDialog(); private static SaveFileDialog dlgSave = new SaveFileDialog(); private static FolderBrowserDialog dlgFolder = new FolderBrowserDialog(); /// <summary> /// Displays a simple Information or Error message to the user. /// </summary> /// <param name="msg">String text that is to be displayed in the MessageBox</param> /// <param name="isError">If true, Error icon is displayed. If false, Information icon is displayed.</param> public void ShowMessage(string msg, bool isError) { if(isError) System.Windows.MessageBox.Show(msg, "Your Project Title", MessageBoxButton.OK, MessageBoxImage.Error); else System.Windows.MessageBox.Show(msg, "Your Project Title", MessageBoxButton.OK, MessageBoxImage.Information); } /// <summary> /// Displays a Yes/No MessageBox.Returns true if user clicks Yes, otherwise false. /// </summary> /// <param name="msg"></param> /// <returns></returns> public bool AskBooleanQuestion(string msg) { var Result = System.Windows.MessageBox.Show(msg, "Your Project Title", MessageBoxButton.YesNo, MessageBoxImage.Question) == MessageBoxResult.Yes; return Result; } /// <summary> /// Displays Save dialog. User can specify file filter, initial directory and dialog title. Returns full path of the selected file if /// user clicks Save button. Returns null if user clicks Cancel button. /// </summary> /// <param name="filter"></param> /// <param name="initDir"></param> /// <param name="title"></param> /// <param name="fileName"></param> /// <returns></returns> public string ShowSave(string filter, string initDir = "", string title = "", string fileName = "") { if (!string.IsNullOrEmpty(title)) dlgSave.Title = title; else dlgSave.Title = "Save"; if (!string.IsNullOrEmpty(fileName)) dlgSave.FileName = fileName; else dlgSave.FileName = ""; dlgSave.Filter = filter; if (!string.IsNullOrEmpty(initDir)) dlgSave.InitialDirectory = initDir; if (dlgSave.ShowDialog() == DialogResult.OK) return dlgSave.FileName; else return null; } public string ShowFolder(string initDir = "") { if (!string.IsNullOrEmpty(initDir)) dlgFolder.SelectedPath = initDir; if (dlgFolder.ShowDialog() == DialogResult.OK) return dlgFolder.SelectedPath; else return null; } /// <summary> /// Displays Open dialog. User can specify file filter, initial directory and dialog title. Returns full path of the selected file if /// user clicks Open button. Returns null if user clicks Cancel button. /// </summary> /// <param name="filter"></param> /// <param name="initDir"></param> /// <param name="title"></param> /// <returns></returns> public string ShowOpen(string filter, string initDir = "", string title = "") { if (!string.IsNullOrEmpty(title)) dlgOpen.Title = title; else dlgOpen.Title = "Open"; dlgOpen.Multiselect = false; dlgOpen.Filter = filter; if (!string.IsNullOrEmpty(initDir)) dlgOpen.InitialDirectory = initDir; if (dlgOpen.ShowDialog() == DialogResult.OK) return dlgOpen.FileName; else return null; } /// <summary> /// Shows Settings dialog. /// </summary> /// <returns>true if User clicks OK button, otherwise false.</returns> public bool ShowSettings() { var w = new SettingsWindow(); MakeChild(w); //Show this dialog as child of Microsoft Word window. var Result = w.ShowDialog().Value; return Result; } /// <summary> /// Prompts user for a single value input. First parameter specifies the message to be displayed in the dialog /// and the second string specifies the default value to be displayed in the input box. /// </summary> /// <param name="m"></param> public string AskStringQuestion(string msg, string default_value) { string Result = null; InputBox w = new InputBox(); MakeChild(w); if (w.ShowDialog(msg, default_value).Value) Result = w.Value; return Result; } /// <summary> /// Sets Word window as parent of the specified window. /// </summary> /// <param name="w"></param> private static void MakeChild(System.Windows.Window w) { IntPtr HWND = Process.GetCurrentProcess().MainWindowHandle; var helper = new WindowInteropHelper(w) { Owner = HWND }; } } While some of these functions are generic (ShowMessage, AskBooleanQuestion etc.), others are specific to this project and use custom Windows. You can add more custom windows in the same fashion. The key is to keep UI-specific elements in the View layer and just expose the returned data using POCOs in the VM layer. Perform IoC Registration your interface in the View layer using this class. You can do this in your main view's constructor (after InitializeComponent() call): SimpleIoc.Default.Register<IDialogService, DialogPresenter>(); There you go. You now have access to all your dialog functionality at both VM and View layers. Your VM layer can call these functions like this: var NoTrump = ViewModelLocator.DialogService.AskBooleanQuestion("Really stop the trade war???", ""); So clean you see. The VM layer doesn't know nothing about how a Yes/No question will be presented to the user by the UI layer and can still successfully work with the returned result from the dialog.

其他免费福利

For writing unit test, you can provide a custom implementation of IDialogService in your Test project and register that class in IoC in the constructor your test class. You'll need to import some namespaces such as Microsoft.Win32 to access Open and Save dialogs. I have left them out because there is also a WinForms version of these dialogs available, plus someone might want to create their own version. Also note that some of the identifier used in DialogPresenter are names of my own windows (e.g. SettingsWindow). You'll need to either remove them from both the interface and implementation or provide your own windows. If your VM performs multi-threading, call MVVM Light's DispatcherHelper.Initialize() early in your application's life cycle. Except for DialogPresenter which is injected in the View layer, other ViewModals should be registered in ViewModelLocator and then a public static property of that type should be exposed for the View layer to consume. Something like this: public static SettingsVM Settings => SimpleIoc.Default.GetInstance<SettingsVM>(); For the most part, your dialogs should not have any code-behind for stuff like binding or setting DataContext etc. You shouldn't even pass things as constructor parameters. XAML can do that all for you, like this: <Window x:Class="YourViewNamespace.SettingsWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:local="clr-namespace:YourViewProject" xmlns:vm="clr-namespace:YourVMProject;assembly=YourVMProject" DataContext="{x:Static vm:ViewModelLocator.Settings}" d:DataContext="{d:DesignInstance Type=vm:SettingsVM}" /> Setting DataContext this way gives you all kinds of design-time benefits such as Intellisense and auto-completion.

希望这对大家都有帮助。

我认为视图可以有代码来处理来自视图模型的事件。

根据事件/场景的不同，它还可以具有订阅视图模型事件的事件触发器，以及响应中要调用的一个或多个操作。

为什么不只是在VM中引发一个事件，然后在视图中订阅该事件呢?这将保持应用程序逻辑和视图分离，并且仍然允许您为对话框使用子窗口。