在询问任务或对话框的视图模型应该是什么样子时，我也在思考一个类似的问题。

我目前的解决方案是这样的:

public class SelectionTaskModel<TChoosable> : ViewModel
    where TChoosable : ViewModel
{
    public SelectionTaskModel(ICollection<TChoosable> choices);
    public ReadOnlyCollection<TChoosable> Choices { get; }
    public void Choose(TChoosable choosen);
    public void Abort();
}

当视图模型决定需要用户输入时，它会调出一个SelectionTaskModel实例，其中包含用户可能的选择。基础设施负责调出相应的视图，该视图在适当的时候根据用户的选择调用Choose()函数。

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。

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。

编辑:10多年后，我可以看出使用Mediator或任何其他消息传递模式在很多层面上都是一个非常糟糕的主意。不要这样做，只需实现Jeffrey的答案或在视图模型中注入一个IDialogService即可。

你应该找个中间人。 Mediator是一种常见的设计模式，在某些实现中也称为Messenger。 它是一种Register/Notify类型的范例，允许ViewModel和Views通过低耦合消息传递机制进行通信。

你应该看看谷歌WPF门徒组，然后搜索调解员。 你会很高兴得到答案的……

但是你可以这样开始:

http://joshsmithonwpf.wordpress.com/2009/04/06/a-mediator-prototype-for-wpf-apps/

享受吧!

编辑:你可以看到这个问题的答案与MVVM轻工具包在这里:

http://mvvmlight.codeplex.com/Thread/View.aspx?ThreadId=209338

我已经实现了一个从ViewModel监听消息的行为。它基于Laurent Bugnion的解决方案，但由于它不使用代码，而且更可重用，所以我认为它更优雅。

如何使WPF的行为，如果MVVM是支持开箱即用

我也遇到过同样的问题。我已经提出了一种在视图和视图模型之间进行交互的方法。您可以发起从ViewModel向View发送消息，告诉它显示一个消息框，然后它将报告返回结果。然后ViewModel可以响应从View返回的结果。

我在博客中对此进行了说明: