问题描述
我这里有代码，曾经在 Autofac 2.6 中工作，但现在在 Autofac 6.2 中不再工作：
class Program
{
static void Main(string[] args)
{
Holder holder = null;
Build(c =>
{
holder = new Holder() { Verifiers = c.Resolve<Verifiers>() };
});
var res = holder.Verifiers;
Console.WriteLine("Success");
}
private static void Build(Action<IContainer> container)
{
var builder = new ContainerBuilder();
builder.RegisterassemblyTypes(typeof(Verifiers).Assembly).AsSelf().AsImplementedInterfaces();
builder.RegisterType<ConsoleOutput>().As<IoUtput>();
builder.RegisterGeneric(typeof(Entitydisplay<>.Params));
builder.RegisterGeneric(typeof(EntitydisplayFactory<,>));
builder.Register<Func<displayFactories>>(c => () => new displayFactories() { Instances = c.Resolve<IEntitydisplayFactory<object>>() });
container(builder.Build());
}
}
public interface IoUtput
{
void Write(string content);
}
public class ConsoleOutput : IoUtput
{
public ConsoleOutput()
{
}
public void Write(string content)
{
Console.WriteLine(content);
}
}
public interface IEntitydisplay
{
void display(object parameter);
}
public class Entitydisplay<T> : IEntitydisplay
{
public struct Params
{
private readonly IoUtput _output;
public Params(IoUtput output)
{
_output = output;
}
}
private readonly T _entity;
public Entitydisplay(T entity)
{
_entity = entity;
}
public void display(object parameter)
{
}
}
public interface IEntitydisplayFactory<in T>
{
IEntitydisplay Create(T entity);
}
public class InstanceEntitydisplayFactory : EntitydisplayFactory<object,object>
{
public InstanceEntitydisplayFactory(Entitydisplay<object>.Params parameters) : base(parameters)
{
}
}
public class EntitydisplayFactory<T,I> : IEntitydisplayFactory<T>
{
private readonly Entitydisplay<T>.Params _param;
public EntitydisplayFactory(Entitydisplay<T>.Params parameters)
{
_param = parameters;
}
public IEntitydisplay Create(T entity)
{
return new Entitydisplay<T>(entity);
}
}
public class displayFactories
{
public IEntitydisplayFactory<object> Instances { get; set; }
}
public class Verifiers
{
private readonly displayFactories _displayFunc;
public Verifiers(Func<displayFactories> displayFunc)
{
_displayFunc = displayFunc();
}
public void Show()
{
displayFactories res = _displayFunc;
res.Instances.Create(null);
}
}
public class Holder
{
public Verifiers Verifiers { get; set; }
}
在 Autofac 6.2 中抛出的异常是
> Autofac.Core.DependencyResolutionException HResult=0x80131500
> Message=An exception was thrown while activating
> AutofacTest46.InstanceEntitydisplayFactory. Source=Autofac
> StackTrace: at
> Autofac.Core.Resolving.Middleware.ActivatorErrorHandlingMiddleware.Execute(ResolveRequestContext
> context,Action`1 next) at
> Autofac.Core.Resolving.Pipeline.ResolvePipelineBuilder.<>c__displayClass14_0.<BuildPipeline>b__1(ResolveRequestContext
> ctxt) at
> Autofac.Core.Pipeline.ResolvePipeline.Invoke(ResolveRequestContext
> ctxt) at
> Autofac.Core.Resolving.Middleware.RegistrationPipelineInvokeMiddleware.Execute(ResolveRequestContext
> context,Action`1 next) at
> Autofac.Core.Resolving.Pipeline.ResolvePipelineBuilder.<>c__displayClass14_0.<BuildPipeline>b__1(ResolveRequestContext
> ctxt) at
> Autofac.Core.Resolving.Middleware.SharingMiddleware.Execute(ResolveRequestContext
> context,Action`1 next) at
> Autofac.Core.Resolving.Pipeline.ResolvePipelineBuilder.<>c__displayClass14_0.<BuildPipeline>b__1(ResolveRequestContext
> ctxt) at
> Autofac.Core.Resolving.Middleware.ScopeSelectionMiddleware.Execute(ResolveRequestContext
> context,Action`1 next) at
> Autofac.Core.Resolving.Pipeline.ResolvePipelineBuilder.<>c__displayClass14_0.<BuildPipeline>b__1(ResolveRequestContext
> ctxt) at
> Autofac.Core.Resolving.Middleware.CircularDependencyDetectorMiddleware.Execute(ResolveRequestContext
> context,Action`1 next) at
> Autofac.Core.Resolving.Pipeline.ResolvePipelineBuilder.<>c__displayClass14_0.<BuildPipeline>b__1(ResolveRequestContext
> ctxt) at
> Autofac.Core.Pipeline.ResolvePipeline.Invoke(ResolveRequestContext
> ctxt) at
> Autofac.Core.Resolving.ResolveOperation.GetorCreateInstance(ISharingLifetimeScope
> currentOperationScope,ResolveRequest request) at
> Autofac.Core.Resolving.Pipeline.DefaultResolveRequestContext.ResolveComponent(ResolveRequest
> request) at
> Autofac.ResolutionExtensions.TryResolveService(IComponentContext
> context,Service service,IEnumerable`1 parameters,Object& instance)
> at Autofac.ResolutionExtensions.ResolveService(IComponentContext
> context,IEnumerable`1 parameters) at
> Autofac.ResolutionExtensions.Resolve[TService](IComponentContext
> context,IEnumerable`1 parameters) at
> Autofac.ResolutionExtensions.Resolve[TService](IComponentContext
> context) at
> AutofacTest46.Program.<>c__displayClass1_0.<Build>b__1() in D:\.net
> Samples project\May 2021\AutofacTest46\Program.cs:line 34 at
> AutofacTest46.Verifiers..ctor(Func`1 displayFunc) in D:\.net Samples
> project\May 2021\AutofacTest46\Outputs.cs:line 94 at
> Autofac.Core.Activators.Reflection.BoundConstructor.Instantiate()
>
> This exception was originally thrown at this call stack:
> [External Code]
>
> Inner Exception 1: ArgumentException: Expression of type
> 'AutofacTest46.Entitydisplay`1+Params[System.Object]' cannot be used
> for return type 'System.Object'
解决方法
问题在于 EntityDisplay<>.Params 是一种值类型 - struct。将其更改为 class 就可以了。
由于 DI 和反射以及其他目前结合在一起的方式，我们必须能够将基于反射的操作的输出转换为 object。 You can see the current wire-up code here. 不幸的是，值类型的构造函数调用程序不返回 object，因此我们无法解析它，一切都崩溃了。
我们可能会为此接受带有修复代码的拉取请求，但是人们通常不会对值类型进行 DI。
无论如何，切换到 class 就可以了。
顺便说一句，这有点难以解决 - 在未来的问题中它可能有助于减少重复（例如，您根本不需要 Holder 类，它只是噪音；您不需要 Verifiers 等。在问题中的异常消息上获得更清晰的格式也会有所帮助，并确保包含所有内部异常。重要的关键是指向构造函数的内部异常调用者。我只能通过复制/粘贴此代码并调试来看到它，不幸的是，我通常没有时间这样做。否则我不得不继续回答这个问题。