每个匹配生存期范围的实例，默认值

Question

我想在 Autofac 中为每个匹配的生存期范围注册提供一个实例，但偶尔需要从全局容器（其中没有匹配的生存期范围）请求一个实例。在不存在匹配生存期范围的情况下，我想提供一个顶级实例，而不是引发异常。

这可能吗？

Answer 1

我认为您最好通过引入新的终身选项来扩展Autofac。我采用了Autofac源并对其进行了一点修改：

public static class RegistrationBuilderExtensions
{
    public static IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> InstancePerMatchingOrRootLifetimeScope<TLimit, TActivatorData, TRegistrationStyle>(this IRegistrationBuilder<TLimit, TActivatorData, TRegistrationStyle> builder, params object[] lifetimeScopeTag)
    {
        if (lifetimeScopeTag == null) throw new ArgumentNullException("lifetimeScopeTag");
        builder.RegistrationData.Sharing = InstanceSharing.Shared;
        builder.RegistrationData.Lifetime = new MatchingScopeOrRootLifetime(lifetimeScopeTag);
        return builder;
    }
}
public class MatchingScopeOrRootLifetime: IComponentLifetime
{
    readonly object[] _tagsToMatch;
    public MatchingScopeOrRootLifetime(params object[] lifetimeScopeTagsToMatch)
    {
        if (lifetimeScopeTagsToMatch == null) throw new ArgumentNullException("lifetimeScopeTagsToMatch");
        _tagsToMatch = lifetimeScopeTagsToMatch;
    }
    public ISharingLifetimeScope FindScope(ISharingLifetimeScope mostNestedVisibleScope)
    {
        if (mostNestedVisibleScope == null) throw new ArgumentNullException("mostNestedVisibleScope");
        var next = mostNestedVisibleScope;
        while (next != null)
        {
            if (_tagsToMatch.Contains(next.Tag))
                return next;
            next = next.ParentLifetimeScope;
        }
        return mostNestedVisibleScope.RootLifetimeScope;
    }
}

只需将这些类添加到项目中，并将组件注册为：

builder.RegisterType<A>.InstancePerMatchingOrRootLifetimeScope("TAG");

我自己没有尝试过，但它应该有效。

Answer 2

可能的解决方案是在子生存期内覆盖注册。

样本：

public enum Scopes
{
    TestScope
}
public class Test
{
   public string Description { get; set; }
}
public class Tester
{
    public void DoTest()
    {
        ContainerBuilder builder = new ContainerBuilder();
        builder.RegisterType<Test>()
            .OnActivating(args => args.Instance.Description = "FromRoot")
            .SingleInstance();
        var container = builder.Build();
        var scope = container.BeginLifetimeScope(Scopes.TestScope, b => b
            .RegisterType<Test>()
            .InstancePerMatchingLifetimeScope(Scopes.TestScope)
            .OnActivating(args => args.Instance.Description = "FromScope"));
        var test1 = container.Resolve<Test>();
        Console.WriteLine(test1.Description); //writes FromRoot
        var test2 = scope.Resolve<Test>();
        Console.WriteLine(test2.Description); //writes FromScope
        Console.ReadLine();
    }
}

Answer 3

根容器本身是一个生命周期范围，其标记名称为 ： root ，在 LifetimeScope.RootTag 中定义

所以你可以做：

using Autofac.Core.Lifetime;
builder.RegisterType<Service>().As<IService>()
    .InstancePerMatchingLifetimeScope(LifetimeScope.RootTag, "foobar");