如何在 Avalonia.ReactiveUI 中使用 Autofac 作为 DI 容器？

Question

我正在尝试使用 Autofac 覆盖在 Avalonia 和 ReactiveUI 中使用的 DI 容器。到目前为止，我已经尝试关注instructions in the Splat.Autofac repository，但我无法让 Avalonia 工作。

作为一个工作示例，我采用了HelloWorld example from the ReactiveUI.Samples 存储库。

我可以想到两个地方来覆盖 Splat。在App.xaml.cs 中OnFrameworkInitializationCompleted 方法中：

using System.Reflection;

using Autofac;

using Avalonia;
using Avalonia.Markup.Xaml;
using Avalonia.ReactiveUI;
using Avalonia.Threading;

using ReactiveUI;

using Splat;
using Splat.Autofac;

namespace ReactiveAvalonia.HelloWorld {
    public class App : Application {
        public override void Initialize() {
            AvaloniaXamlLoader.Load(this);
        }

        public override void OnFrameworkInitializationCompleted()
        {
            // Build a new Autofac container.
            var builder = new ContainerBuilder();
            builder.RegisterAssemblyTypes(Assembly.GetExecutingAssembly()).AsImplementedInterfaces();

            // Use Autofac for ReactiveUI dependency resolution.
            // After we call the method below, Locator.Current and
            // Locator.CurrentMutable start using Autofac locator.
            AutofacDependencyResolver resolver = new AutofacDependencyResolver(builder);
            Locator.SetLocator(resolver);

            // These .InitializeX() methods will add ReactiveUI platform 
            // registrations to your container. They MUST be present if
            // you *override* the default Locator.
            Locator.CurrentMutable.InitializeSplat();
            Locator.CurrentMutable.InitializeReactiveUI();

            var container = builder.Build();
            resolver.SetLifetimeScope(container);
        }
    }
}

但是在运行时，启动失败并出现以下异常：

System.ArgumentException: '不知道如何检测 ReactiveAvalonia.HelloWorld.MainView 何时激活/停用，您可能需要实现 IActivationForViewFetcher'

我的另一个想法是在Program.cs 的Main 中进行覆盖：

using System.Reflection;

using Autofac;

using Avalonia;
using Avalonia.Controls;
using Avalonia.Logging.Serilog;
using Avalonia.ReactiveUI;
using Avalonia.Threading;

using ReactiveUI;

using Splat;
using Splat.Autofac;

namespace ReactiveAvalonia.HelloWorld {

    // You may want to start here:
    // https://reactiveui.net/docs/getting-started/

    class Program {
        // http://avaloniaui.net/docs/reactiveui/
        // https://github.com/AvaloniaUI/Avalonia/wiki/Application-lifetimes
        public static AppBuilder BuildAvaloniaApp() {
            return AppBuilder
                .Configure<App>()
                .UseReactiveUI()
                .UsePlatformDetect()
                .LogToDebug();
        }

        private static void AppMain(Application app, string[] args) {
            app.Run(new MainView());
        }

        public static void Main(string[] args) {
            // Build a new Autofac container.
            var builder = new ContainerBuilder();
            builder.RegisterAssemblyTypes(Assembly.GetExecutingAssembly()).AsImplementedInterfaces();

            // Use Autofac for ReactiveUI dependency resolution.
            // After we call the method below, Locator.Current and
            // Locator.CurrentMutable start using Autofac locator.
            AutofacDependencyResolver resolver = new AutofacDependencyResolver(builder);
            Locator.SetLocator(resolver);

            // These .InitializeX() methods will add ReactiveUI platform 
            // registrations to your container. They MUST be present if
            // you *override* the default Locator.
            Locator.CurrentMutable.InitializeSplat();
            Locator.CurrentMutable.InitializeReactiveUI();

            var container = builder.Build();
            resolver.SetLifetimeScope(container);

            BuildAvaloniaApp().Start(AppMain, args);
        }
    }
}

但这失败了，还有一个例外：

System.Exception: '容器已经构建并且生命周期范围设置，所以不能再修改它。'

我该怎么做才能让它发挥作用？

Answer 1

通常，Avalonia 文档会告诉您使用 AppBuilder 上的 UseReactiveUI extension method 才能使用 ReactiveUI。它的作用是将一些 Avalonia 组件注册到 DI 容器：

    public static TAppBuilder UseReactiveUI<TAppBuilder>(this TAppBuilder builder)
        where TAppBuilder : AppBuilderBase<TAppBuilder>, new()
    {
        return builder.AfterPlatformServicesSetup(_ =>
        {
            RxApp.MainThreadScheduler = AvaloniaScheduler.Instance;
            Locator.CurrentMutable.RegisterConstant(new AvaloniaActivationForViewFetcher(), typeof(IActivationForViewFetcher));
            Locator.CurrentMutable.RegisterConstant(new AutoDataTemplateBindingHook(), typeof(IPropertyBindingHook));
        });
    }

对于问题中的两种解决方案，出现问题的可能方式有两种：

在App 中设置 Autofac

当您在 OnFrameworkInitializationCompleted 中设置 Autofac 时，这会发生在 UseReactiveUI 中的注册设置完成之后，基本上会覆盖它们。

如果您在覆盖 DI 容器后再次添加这些代码行，应用程序将启动：

    public override void OnFrameworkInitializationCompleted()
    {
        // Build a new Autofac container.
        var builder = new ContainerBuilder();
        builder.RegisterAssemblyTypes(Assembly.GetExecutingAssembly()).AsImplementedInterfaces();

        // Use Autofac for ReactiveUI dependency resolution.
        // After we call the method below, Locator.Current and
        // Locator.CurrentMutable start using Autofac locator.
        AutofacDependencyResolver resolver = new AutofacDependencyResolver(builder);
        Locator.SetLocator(resolver);

        // These .InitializeX() methods will add ReactiveUI platform 
        // registrations to your container. They MUST be present if
        // you *override* the default Locator.
        Locator.CurrentMutable.InitializeSplat();
        Locator.CurrentMutable.InitializeReactiveUI();

        Locator.CurrentMutable.RegisterConstant(new AvaloniaActivationForViewFetcher(), typeof(IActivationForViewFetcher));
        Locator.CurrentMutable.RegisterConstant(new AutoDataTemplateBindingHook(), typeof(IPropertyBindingHook));
        RxApp.MainThreadScheduler = AvaloniaScheduler.Instance;

        var container = builder.Build();
        resolver.SetLifetimeScope(container);
    }

在Main 中设置 Autofac

在这里，我们已经在 Avalonia 尝试注册其组件之前覆盖了 DI 容器，此时，Autofac 容器已经创建，并且它是只读的，这会导致第二个异常。同样，这可以通过与其他代码一起进行相同的注册来解决。那么AppBuilder.UseReactiveUI扩展方法可以省略：

using System.Reflection;

using Autofac;

using Avalonia;
using Avalonia.Controls;
using Avalonia.Logging.Serilog;
using Avalonia.ReactiveUI;
using Avalonia.Threading;

using ReactiveUI;

using Splat;
using Splat.Autofac;

namespace ReactiveAvalonia.HelloWorld {

    // You may want to start here:
    // https://reactiveui.net/docs/getting-started/

    class Program {
        // http://avaloniaui.net/docs/reactiveui/
        // https://github.com/AvaloniaUI/Avalonia/wiki/Application-lifetimes
        public static AppBuilder BuildAvaloniaApp() {
            return AppBuilder
                .Configure<App>()
                //.UseReactiveUI()
                .UsePlatformDetect()
                .LogToDebug();
        }

        private static void AppMain(Application app, string[] args) {
            app.Run(new MainView());
        }

        public static void Main(string[] args) {
            // Build a new Autofac container.
            var builder = new ContainerBuilder();
            builder.RegisterAssemblyTypes(Assembly.GetExecutingAssembly()).AsImplementedInterfaces();

            // Use Autofac for ReactiveUI dependency resolution.
            // After we call the method below, Locator.Current and
            // Locator.CurrentMutable start using Autofac locator.
            AutofacDependencyResolver resolver = new AutofacDependencyResolver(builder);
            Locator.SetLocator(resolver);

            // These .InitializeX() methods will add ReactiveUI platform 
            // registrations to your container. They MUST be present if
            // you *override* the default Locator.
            Locator.CurrentMutable.InitializeSplat();
            Locator.CurrentMutable.InitializeReactiveUI();

            Locator.CurrentMutable.RegisterConstant(new AvaloniaActivationForViewFetcher(), typeof(IActivationForViewFetcher));
            Locator.CurrentMutable.RegisterConstant(new AutoDataTemplateBindingHook(), typeof(IPropertyBindingHook));
            RxApp.MainThreadScheduler = AvaloniaScheduler.Instance;

            var container = builder.Build();
            resolver.SetLifetimeScope(container);
            BuildAvaloniaApp().Start(AppMain, args);
        }
    }
}

扩展方法

现在，在类似于我们用来设置 Splat 和 ReactiveUI 的扩展方法中，这看起来会更好：

    public static void InitializeAvalonia(this IMutableDependencyResolver resolver)
    {
        resolver.RegisterConstant(new AvaloniaActivationForViewFetcher(), typeof(IActivationForViewFetcher));
        resolver.RegisterConstant(new AutoDataTemplateBindingHook(), typeof(IPropertyBindingHook));
        RxApp.MainThreadScheduler = AvaloniaScheduler.Instance;
    }  

和

    public static void Main(string[] args) {
        // Build a new Autofac container.
        var builder = new ContainerBuilder();
        builder.RegisterAssemblyTypes(Assembly.GetExecutingAssembly()).AsImplementedInterfaces();

        // Use Autofac for ReactiveUI dependency resolution.
        // After we call the method below, Locator.Current and
        // Locator.CurrentMutable start using Autofac locator.
        AutofacDependencyResolver resolver = new AutofacDependencyResolver(builder);
        Locator.SetLocator(resolver);

        // These .InitializeX() methods will add ReactiveUI platform 
        // registrations to your container. They MUST be present if
        // you *override* the default Locator.
        Locator.CurrentMutable.InitializeSplat();
        Locator.CurrentMutable.InitializeReactiveUI();
        Locator.CurrentMutable.InitializeAvalonia();

        var container = builder.Build();
        resolver.SetLifetimeScope(container);
        BuildAvaloniaApp().Start(AppMain, args);
    }