MEF和WPF无棱镜

Question

有人可以告诉我一个在app.xaml.cs文件中构建MEF合成容器的示例，而无需使用棱镜或控制台应用程序，这没有问题。

导出有效，但导入无效，我看到的所有示例仅适用于我不想使用的Prism。 如果在App.xaml.cs文件中，导入将起作用，但是我不明白为什么在MainWindow.cs中导入将不起作用，并且一切都在根程序集中。

如果我在MainWindow构造函数中进行合成，则可以编写它，但是如果可能的话，我想在app.xaml.cs中编写。

这是一个示例（我实际上正在使用mvvm，但此示例的行为与后面的代码相同）。

 public partial class App : Application
{
    public App()
    {
        ShutdownMode = ShutdownMode = ShutdownMode.OnMainWindowClose;

    }

    protected override void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);



        Compose();

       var window = new MainWindow();
        window.Show();

    }

    public void Compose()
    {
        var catalog = new AggregateCatalog(new AssemblyCatalog(Assembly.GetExecutingAssembly()), new DirectoryCatalog("."));
        var container = new CompositionContainer(catalog);
        container.ComposeParts(this);
    }


}

 [Export]
public class MessagePlugin
{
    public string GetMessage()
    {
        return "Successfully composed message";
    }

}

 public partial class MainWindow : Window
{
    [Import]
    public MessagePlugin plugin { get; set; }

    public MainWindow()
    {
        InitializeComponent();
        Loaded += MainWindow_Loaded;

    }


    private void MainWindow_Loaded(object sender, RoutedEventArgs e)
    {
        var p = plugin; <-------------------------------NULL
        MessageBox.Show(p.GetMessage());

    }
}

Answer 1

public partial class App : Application
{
   private CompositionContainer container;

    [Import(typeof(Window))]
    public Window TheMainWindow { get; set; }


    public App()
    {
        ShutdownMode = ShutdownMode = ShutdownMode.OnMainWindowClose;
    }


    protected override void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);

        TheMainWindow = new MainWindow();

        Compose();

        Application.Current.MainWindow = TheMainWindow;
        Application.Current.MainWindow.Show();

    }

    public void Compose()
    {
        var catalog = new AggregateCatalog();
        catalog.Catalogs.Add(new AssemblyCatalog(typeof(App).Assembly));  
        container = new CompositionContainer(catalog);
        container.ComposeParts(this);
    }

}

[Export（typeof（Window））]公共部分类MainWindow：Window {[Import]公共MessagePlugin插件{get; 组; }

    public MainWindow()
    {
        InitializeComponent();
        Loaded += MainWindow_Loaded;

    }


    private void MainWindow_Loaded(object sender, RoutedEventArgs e)
    {
        var p = plugin;

        if (p != null)
        {
            MessageBox.Show(p.GetMessage());
        }
        else
        {
            MessageBox.Show("Plugin NOT Composed");
        }


    }
}