Xamarin Forms/Prism/Shiny中DryIoc服务注册ContainerException异常排查

启动iOS应用时抛出DryIoc容器异常，提示无法解析IInitService服务：

DryIoc.ContainerException: code: Error.UnableToResolveUnknownService;
message: Unable to resolve resolution root PS.Forms.VoiceApp.Base.Interfaces.IInitService
  from container with scope {Name=null}
 with Rules with {TrackingDisposableTransients, UseDynamicRegistrationsAsFallbackOnly, FuncAndLazyWithoutRegistration, SelectLastRegisteredFactory} and without {ThrowOnRegisteringDisposableTransient, UseFastExpressionCompilerIfPlatformSupported}
 with FactorySelector=SelectLastRegisteredFactory
 with Made={FactoryMethod=ConstructorWithResolvableArguments}
Where no service registrations found
  and no dynamic registrations found in 1 of Rules.DynamicServiceProviders
  and nothing found in 0 of Rules.UnknownServiceResolvers
  at DryIoc.Throw.It (System.Int32 error, System.Object arg0, System.Object arg1, System.Object arg2, System.Object arg3) [0x00000] in /_/src/DryIoc/Container.cs:13642
  at DryIoc.Container.TryThrowUnableToResolve (DryIoc.Request request) [0x0006d] in /_/src/DryIoc/Container.cs:1088
  at DryIoc.Container.DryIoc.IContainer.ResolveFactory (DryIoc.Request request) [0x00072] in /_/src/DryIoc/Container.cs:1068
  at DryIoc.Container.ResolveAndCache (System.Int32 serviceTypeHash, System.Type serviceType, DryIoc.IfUnresolved ifUnresolved) [0x00021] in /_/src/DryIoc/Container.cs:367
  at DryIoc.Container.DryIoc.IResolver.Resolve (System.Type serviceType, DryIoc.IfUnresolved ifUnresolved) [0x0011c] in /_/src/DryIoc/Container.cs:356
  at DryIoc.Container.DryIoc.IResolver.Resolve (System.Type serviceType, System.Object serviceKey, DryIoc.IfUnresolved ifUnresolved, System.Type requiredServiceType, DryIoc.Request preResolveParent, System.Object[] args) [0x00039] in /_/src/DryIoc/Container.cs:428
  at DryIoc.Resolver.Resolve (DryIoc.IResolver resolver, System.Type serviceType, System.Object[] args, DryIoc.IfUnresolved ifUnresolved, System.Type requiredServiceType, System.Object serviceKey) [0x00000] in /_/src/DryIoc/Container.cs:8087
  at Prism.DryIoc.DryIocContainerExtension.Resolve (System.Type type, System.ValueTuple`2[System.Type,System.Object][] parameters) [0x0001c] in /_/src/Containers/Prism.DryIoc.Shared/DryIocContainerExtension.cs:294

我在AppDelegate.cs中注册了IInitService的iOS实现IOSInitService：

public override bool FinishedLaunching(UIApplication application, NSDictionary launchOptions) {
            this.PreventLinkerFromStrippingCommonLocalizationReferences();
            Rg.Plugins.Popup.Popup.Init();
            this.ShinyFinishedLaunching(new VoiceAppStartup {
                RegisterPlatformServices = services =>
                {
                    services.AddSingleton<IInitService, IOSInitService>();
                }
            });
            global::Xamarin.Forms.Forms.Init();
            FormsControls.Touch.Main.Init();
            this.LoadApplication(new App());
            return base.FinishedLaunching(application, launchOptions);
        }

同时在App.xaml.cs中注册了其他跨平台服务（运行正常）：

protected override void RegisterTypes(IContainerRegistry containerRegistry) {
            containerRegistry.RegisterPopupNavigationService();
            containerRegistry.RegisterSingleton<IAppInfo, AppInfoImplementation>();
            containerRegistry.RegisterSingleton<IShare, ShareImplementation>();
...}

请问异常原因是什么？是否遗漏了某些步骤？

• 服务注册容器不匹配
  你通过Shiny的RegisterPlatformServices注册的服务，并未进入Prism使用的DryIoc容器实例。Prism的容器是在new App()初始化时创建的，Shiny的注册逻辑独立于Prism容器，导致服务无法被Prism容器识别。
  解决方式：使用Prism的平台特定初始化机制：

  1. 在iOS项目中实现IPlatformInitializer接口：

     using Prism.Ioc;
     
     public class iOSPlatformInitializer : IPlatformInitializer
     {
         public void RegisterTypes(IContainerRegistry containerRegistry)
         {
             containerRegistry.RegisterSingleton<IInitService, IOSInitService>();
         }
     }
     

  2. 修改App.xaml.cs的构造函数，接收平台初始化器：

     public App(IPlatformInitializer initializer) : base(initializer)
     {
     }
     

  3. 在AppDelegate.cs中调整LoadApplication的调用：

     this.LoadApplication(new App(new iOSPlatformInitializer()));
     

• iOS链接器剥离了实现类
  iOS的链接器会移除未被直接引用的代码，如果IOSInitService没有被代码直接实例化，链接器可能会将其从编译包中移除，导致容器找不到实现。
  解决方式：

  • 给IOSInitService添加[Preserve]特性：

    using Xamarin.Forms;
    
    [Preserve(AllMembers = true)]
    public class IOSInitService : IInitService
    {
        // 实现代码
    }
    

  • 或者在iOS项目的Linker.xml中添加保留规则：

    <assembly fullname="你的iOS项目名称">
        <type fullname="你的命名空间.IOSInitService" preserve="all"/>
    </assembly>
    

• 注册时机错误
  当前代码先执行Shiny初始化，再加载App，Prism容器可能在Shiny注册时还未创建，导致服务未被正确注入。通过Prism的平台初始化器注册，可以确保服务在Prism容器初始化时被注册。

• 接口与实现的引用/拼写问题
  检查IInitService所在的程序集是否被iOS项目正确引用，IOSInitService是否正确实现了IInitService，确认接口名称、命名空间没有拼写错误。

内容的提问来源于stack exchange，提问作者user16291322