c# - Seemann 依赖注入(inject)， "Three Calls Pattern"与服务定位器反模式

Question

我使用依赖注入(inject) (DI) 和 Ninject 作为 DI 容器创建了一个 WinForms MVC 应用程序。基本架构如下

Program.cs(WinForms 应用程序的主要入口点):

static class Program
{
    [STAThread]
    static void Main()
    {
        ...

        CompositionRoot.Initialize(new DependencyModule());
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(CompositionRoot.Resolve<ApplicationShellView>());
    }
}

DependencyModule.cs

public class DependencyModule : NinjectModule
{
    public override void Load()
    {
        Bind<IApplicationShellView>().To<ApplicationShellView>();
        Bind<IDocumentController>().To<SpreadsheetController>();
        Bind<ISpreadsheetView>().To<SpreadsheetView>();
    }
}

CompositionRoot.cs

public class CompositionRoot
{
    private static IKernel ninjectKernel;

    public static void Initialize(INinjectModule module)
    {
        ninjectKernel = new StandardKernel(module);
    }

    public static T Resolve<T>()
    {
        return ninjectKernel.Get<T>();
    }

    public static IEnumerable<T> ResolveAll<T>()
    {
        return ninjectKernel.GetAll<T>();
    }
}

ApplicationShellView.cs(应用程序的主要形式)

public partial class ApplicationShellView : C1RibbonForm, IApplicationShellView
{
    private ApplicationShellController controller; 

    public ApplicationShellView()
    {
        this.controller = new ApplicationShellController(this);
        InitializeComponent();
    }

    public void InitializeView()
    {
        dockPanel.Extender.FloatWindowFactory = new CustomFloatWindowFactory();
        dockPanel.Theme = vS2012LightTheme;
    }

    private void ribbonButtonTest_Click(object sender, EventArgs e)
    {
        controller.OpenNewSpreadsheet();
    }

    public DockPanel DockPanel
    {
        get { return dockPanel; }
    }
}

在哪里

public interface IApplicationShellView
{
    void InitializeView();
    DockPanel DockPanel { get; }
}

ApplicationShellController.cs

public class ApplicationShellController
{
    private IApplicationShellView shellView;

    public ApplicationShellController(IApplicationShellView view)
    {
        this.shellView = view;
    }

    public void OpenNewSpreadsheet(DockState dockState = DockState.Document)
    {
        SpreadsheetController controller = (SpreadsheetController)GetDocumentController("new.xlsx");
        SpreadsheetView view = (SpreadsheetView)controller.New("new.xlsx");
        view.Show(shellView.DockPanel, dockState);
    }

    private IDocumentController GetDocumentController(string path)
    {
        return CompositionRoot.ResolveAll<IDocumentController>()
            .SingleOrDefault(provider => provider.Handles(path));
    }

    public IApplicationShellView ShellView { get { return shellView; } }
}

SpreadsheetController.cs

public class SpreadsheetController : IDocumentController 
{
    private ISpreadsheetView view;

    public SpreadsheetController(ISpreadsheetView view)
    {
        this.view = view;
        this.view.SetController(this);
    }

    public bool Handles(string path)
    {
        string extension = Path.GetExtension(path);
        if (!String.IsNullOrEmpty(extension))
        {
            if (FileTypes.Any(ft => ft.FileExtension.CompareNoCase(extension)))
                return true;
        }
        return false;
    }

    public void SetViewActive(bool isActive)
    {
        ((SpreadsheetView)view).ShowIcon = isActive;
    }

    public IDocumentView New(string fileName)
    {
        // Opens a new file correctly.
    }

    public IDocumentView Open(string path)
    {
        // Opens an Excel file correctly.
    }

    public IEnumerable<DocumentFileType> FileTypes
    {
        get
        {
            return new List<DocumentFileType>()
            {
                new DocumentFileType("CSV",  ".csv" ),
                new DocumentFileType("Excel", ".xls"),
                new DocumentFileType("Excel10", ".xlsx")
            };
        }
    }
}

实现的接口(interface)在哪里

public interface IDocumentController
{
    bool Handles(string path);

    void SetViewActive(bool isActive);

    IDocumentView New(string fileName);

    IDocumentView Open(string path);

    IEnumerable<DocumentFileType> FileTypes { get; }
}

现在与这个 Controller 关联的 View 是

public partial class SpreadsheetView : DockContent, ISpreadsheetView
{
    private IDocumentController controller;

    public SpreadsheetView()
    {
        InitializeComponent();
    }

    private void SpreadsheetView_Activated(object sender, EventArgs e)
    {
        controller.SetViewActive(true);
    }

    private void SpreadsheetView_Deactivate(object sender, EventArgs e)
    {
        controller.SetViewActive(false);
    }

    public void SetController(IDocumentController controller)
    {
        this.controller = controller;
        Log.Trace("SpreadsheetView.SetController(): Controller set successfully");
    }

    public string DisplayName
    {
        get { return Text; }
        set { Text = value; }
    }

    public WorkbookView WorkbookView
    {
        get { return workbookView; }
        set { workbookView = value; }
    }
    ...
}

最后是 View 界面

public interface ISpreadsheetView : IDocumentView
{
    WorkbookView WorkbookView { get; set; } 
}

和

public interface IDocumentView
{
    void SetController(IDocumentController controller);

    string DisplayName { get; set; }

    bool StatusBarVisible { get; set; }
}

现在是我的问题。在 Seemann 的书“.NET 中的依赖注入(inject)”中，他谈到了“三次调用模式”，这就是我在上面试图实现的。代码有效，shell View 显示并通过 MVC 模式我的 Controller 正确打开 View 等。但是，我很困惑，因为上面肯定有“服务定位器反模式”的味道。在 Seemann 的书的第 3 章中，他说

The COMPOSITION ROOT pattern describes where you should use a DI CONTAINER. However, it doesn’t state how to use it. The REGISTER RESOLVE RELEASE pattern addresses this question [...] A DI CONTAINER should be used in three successive phases called Register, Resolve, and Release.

In its pure form, the REGISTER RESOLVE RELEASE pattern states that you should only make a single method call in each phase. Krzysztof Kozimic calls this the Three Calls Pattern.

Configuring a DI CONTAINER in a single method call requires more explanation. The reason that registration of components should happen in a single method call is because you should regard configuration of a DI CONTAINER as a single, atomic action. Once configuration is completed, the container should be regarded as read-only.

这听起来像是被挖出的“服务定位器”，为什么这不被视为服务位置？

---

为了调整我的代码以使用 Contstructor Injection，我将入口代码更改为

[STAThread]
static void Main()
{
    var kernel = new StandardKernel();
    kernel.Bind(t => t.FromThisAssembly()
                      .SelectAllClasses()
                      .BindAllInterfaces());

    FileLogHandler fileLogHandler = new FileLogHandler(Utils.GetLogFilePath());
    Log.LogHandler = fileLogHandler;
    Log.Trace("Program.Main(): Logging initialized");

    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);
    Application.Run(kernel.Get<ApplicationShellView>());
}

使用 Ninject.Extensions.Conventions ，然后我更改了ApplicationShellController为了更正我的代码以注入(inject) IDocumentController s 通过 ctor 注入(inject):

public class ApplicationShellController
{
    private IApplicationShellView shellView;
    private IEnumerable<IDocumentController> controllers; 

    public ApplicationShellController(IApplicationShellView shellView, IEnumerable<IDocumentController> controllers)
    {
        this.shellView = shellView;
        this.controllers = controllers;
        Log.Trace("ApplicationShellController.Ctor(): Shell initialized successfully"); 
    }
    ...
}

在哪里

public class SpreadsheetController : IDocumentController 
{
    private ISpreadsheetView view;

    public SpreadsheetController(ISpreadsheetView view)
    {
        this.view = view;
        this.view.SetController(this);
    }
    ...
}

但这会导致循环依赖，我该如何处理呢？

问题总结:

1. 为什么我最初使用 Ninject 使用“Thee Calls Pattern”和 CompositionRoot.Resolve<T>()服务定位器反模式不好或不同？
2. 如果我想切换到纯 ctor 注入(inject)，如何解决上述循环依赖问题？

非常感谢您的宝贵时间。

Answer 1

在流程的某个时刻，您必须使用服务位置。然而，DI 和 SL 之间的区别在于，在 SL 中，您在请求它们时解析您的服务，而在 DI 中，您在某种工厂(例如 Controller 工厂)中解析它们，然后构造您的对象并通过中的引用。

您应该创建某种基础设施来分派(dispatch)您的命令并使用某种工厂来定位所创建对象所使用的依赖项。

通过这种方式，您的其余代码没有依赖项解析，并且除了构造点外，您都遵循 DI 模式。