3

考虑以下结构作为 Autofac 3.0.0 的注册主体：

class Something
{
    public int Result { get; set; }
}

class SomethingGood : Something
{
    private int _good;
    public int GoodResult {
        get { return _good + Result; }
        set { _good = value; }
    }
}

interface IDo<in T> where T : Something
{
    int Calculate( T input );
}

class MakeSomethingGood : IDo<SomethingGood>
{
    public int Calculate( SomethingGood input ) {
        return input.GoodResult;
    }
}

class ControlSomething
{
    private readonly IDo<Something> _doer;
    public ControlSomething( IDo<Something> doer ) {
        _doer = doer;
    }

    public void Show() {
        Console.WriteLine( _doer.Calculate( new Something { Result = 5 } ) );
    }
}

我正在尝试注册具体类型 MakeSomethingGood ，然后通过逆变接口解决它。

var builder = new ContainerBuilder();
builder.Register( c => new MakeSomethingGood() ).As<IDo<SomethingGood>>();
builder.Register( c => new ControlSomething( c.Resolve<IDo<Something>>() ) ).AsSelf();

var container = builder.Build();
var controller = container.Resolve<ControlSomething>();

...并Resolve失败，因为没有找到组件IDo<Something>

我究竟做错了什么？

谢谢

4

1 回答 1

1

您注册一个IDo<SomethingGood>并尝试解决一个IDo<Something>. 那应该怎么工作？为此，IDo<T>应将其定义为协变：IDo<out T>.

由于IDo<in T>被定义为逆变（使用in关键字），你不能简单地分配一个IDo<SomethingGood>to IDo<Something>。这不会在 C# 中编译：

IDo<SomethingGood> good = new MakeSomethingGood();

// Won't compile
IDo<Something> some = good;

这就是 Autofac 无法解决它的原因，即使使用ContravariantRegistrationSource.

于 2013-02-07T09:45:50.853 回答