c# - RuntimeBinderException - C# .NET 4 动态关键字 - 帮助我理解为什么方法不匹配

Question

我为 HttpModule 构建了一个通用配置系统，它允许可插入的 HTTP header 检查器。作为引用，这里是代码的基本布局——这应该足以让我了解我在做什么:

public interface IHttpHeaderInspectingAuthenticatorFactory<T>
    where T: HttpHeaderInspectingAuthenticatorConfigurationElement
{
    IHttpHeaderInspectingAuthenticator<T> Construct(T config);
}

public class BasicAuthenticationInspectingAuthenticatorFactory :
    IHttpHeaderInspectingAuthenticator<BasicAuthenticationHeaderInspectorConfigurationElement>
{
    public IHttpHeaderInspectingAuthenticator<BasicAuthenticationHeaderInspectorConfigurationElement> Construct(BasicAuthenticationHeaderInspectorConfigurationElement config)
    {
        return new BasicAuthenticationInspectingAuthenticator(config);
    }
}

public class BasicAuthenticationInspectingAuthenticator : HttpHeaderInspectingAuthenticatorBase<BasicAuthenticationHeaderInspectorConfigurationElement>
{
    internal BasicAuthenticationInspectingAuthenticator(BasicAuthenticationHeaderInspectorConfigurationElement config) 
        : base(config) {}

 //snip -- IHttpHeaderInspectingAuthenticator<T> and IHttpHeaderInspectingAuthenticator implementation
}


public class BasicAuthenticationHeaderInspectorConfigurationElement : HttpHeaderInspectingAuthenticatorConfigurationElement
{
 //extra properties
}


public class HttpHeaderInspectingAuthenticatorConfigurationElement : ConfigurationElement
{
 protected override void PostDeserialize()
 {
     base.PostDeserialize();

     //simple verification of info supplied in config
     var t = Type.GetType(Factory);
     if (null == t)
         throw new ConfigurationErrorsException(String.Format("The factory type specified [{0}] cannot be found - check configuration settings", Factory ?? ""));

     if (!typeof(IHttpHeaderInspectingAuthenticatorFactory<>).IsGenericInterfaceAssignableFrom(t))
         throw new ConfigurationErrorsException(String.Format("The factory type specified [{0}] must derive from {1} - check configuration settings", Factory ?? "", typeof(IHttpHeaderInspectingAuthenticatorFactory<>).Name));

     var c = t.GetConstructor(Type.EmptyTypes);
     if (null == c)
         throw new ConfigurationErrorsException(String.Format("The factory type specified [{0}] must have a parameterless constructor - check configuration settings", Factory ?? ""));
 }

 [ConfigurationProperty("factory", IsRequired = true)]
 public string Factory
 {
  get { return (string)this["factory"]; }
  set { this["factory"] = value; }
 }

 //this allows us to use types derived from HttpHeaderInspectingAuthenticatorConfigurationElement
    protected override bool OnDeserializeUnrecognizedAttribute(string name, string value)
    {                    
        ConfigurationProperty property = new ConfigurationProperty(name, typeof(string), value);
        Properties.Add(property);
        base[property] = value;            
        return true;
    }

 public IHttpHeaderInspectingAuthenticator GetInspector()
 {
     dynamic factoryInstance = Activator.CreateInstance(Type.GetType(Factory));
     return factoryInstance.Construct(this);
 }
}

现在问题出现在 GetInspector 调用中——所提供的工厂名称的所有实例都必须实现 IHttpHeaderInspectingAuthenticatorFactor<>(如 PostDeserialize 中的规范)。因此，它们都有一个 Construct 方法，其中提供的类型 T 实际上是实现 GetInspector() 方法的类的实际类型。因此，例如，将在 BasicAuthenticationHeaderInspectorConfigurationElement 的实例上调用 GetInspector——因此“this”将是 BasicAuthenticationHeaderInspectorConfigurationElement 的实例。

但是，对 Construct 的调用失败了。它发现该方法很好，但显然参数类型与抛出的 RuntimeBinderException 不匹配。根据 CallSite.Target，动态代理期望的预期类型似乎是 HttpHeaderInspectingAuthenticatorConfigurationElement——我传递的“this”是 BasicAuthenticationHeaderInspectorConfigurationElement，派生自该基础。

那么是什么给了？我在这里没有得到什么吗？我尝试传递(this as dynamic)或((HttpHeaderInspectingAuthenticatorConfigurationElement)this)——但都因同样的问题而失败。

Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: The best overloaded method match for 'Redcated.Authentication.BasicAuthenticationInspectingAuthenticatorFactory.Construct(Redcated.Authentication.Configuration.BasicAuthenticationHeaderInspectorConfigurationElement)' has some invalid arguments
  at CallSite.Target(Closure , CallSite , Object , HttpHeaderInspectingAuthenticatorConfigurationElement )
  at System.Dynamic.UpdateDelegates.UpdateAndExecute2[T0,T1,TRet](CallSite site, T0 arg0, T1 arg1)
  at Redcated.Authentication.Configuration.HttpHeaderInspectingAuthenticatorConfigurationElement.GetInspector() in D:\Users\ebrown\Documents\Visual Studio 2010\Projects\Utility\source\Authentication Library\Configuration\HttpHeaderInspectingAuthenticatorConfigurationElement.cs:line 79
  at Redcated.Authentication.Configuration.HttpHeaderInspectingAuthenticatorConfigurationElementCollection.<GetInspectors>b__0(HttpHeaderInspectingAuthenticatorConfigurationElement i) in D:\Users\ebrown\Documents\Visual Studio 2010\Projects\Utility\source\Authentication Library\Configuration\HttpHeaderInspectingAuthenticatorConfigurationElementCollection.cs:line 78
  at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
  at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
  at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector)
  at Redcated.Authentication.HttpHeaderInspectingAuthenticationModule.AuthenticateRequest(Object sender, EventArgs e) in D:\Users\ebrown\Documents\Visual Studio 2010\Projects\Utility\source\Authentication Library\HttpHeaderInspectingAuthenticationModule.cs:line 49
  at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
  at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

仅供引用——我已经通过稍微改变接口(interface)的架构来解决这个问题:

public interface IHttpHeaderInspectingAuthenticatorFactory
{
    IHttpHeaderInspectingAuthenticator Construct(HttpHeaderInspectingAuthenticatorConfigurationElement config);
}

public interface IHttpHeaderInspectingAuthenticatorFactory<T> : IHttpHeaderInspectingAuthenticatorFactory
    where T: HttpHeaderInspectingAuthenticatorConfigurationElement
{
    IHttpHeaderInspectingAuthenticator<T> Construct(T config);
}

public abstract class HttpHeaderInspectingAuthenticatorFactoryBase<T> : IHttpHeaderInspectingAuthenticatorFactory<T>
            where T : HttpHeaderInspectingAuthenticatorConfigurationElement
{
    protected static readonly ILog log = LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);

    public abstract IHttpHeaderInspectingAuthenticator<T> Construct(T config);

    public IHttpHeaderInspectingAuthenticator Construct(HttpHeaderInspectingAuthenticatorConfigurationElement config)
    {
        return Construct((T)config);
    }
}

 public class BasicAuthenticationInspectingAuthenticatorFactory :
    HttpHeaderInspectingAuthenticatorFactoryBase<BasicAuthenticationHeaderInspectorConfigurationElement>
{
    public override IHttpHeaderInspectingAuthenticator<BasicAuthenticationHeaderInspectorConfigurationElement> Construct(BasicAuthenticationHeaderInspectorConfigurationElement config)
    {
        return new BasicAuthenticationInspectingAuthenticator(config);
    }
}

当然，GetInspector 调用变成了

public IHttpHeaderInspectingAuthenticator GetInspector()
{
    var factoryInstance = (IHttpHeaderInspectingAuthenticatorFactory)Activator.CreateInstance(Type.GetType(Factory));
    return factoryInstance.Construct(this);
}

所以我认为我的理解一定有失误...希望有人能给出一些启示。

谢谢!

Answer 1

我认为您需要将 this 转换为动态的。例如 factoryInstance.Construct((dynamic)this); 我认为问题是动态调用默认使用缓存委托(delegate)(目标)签名的编译时信息。

因为动态调用的实现是在基类中，它是它用于签名的，但是因为你的后期绑定(bind)签名是一个子类，你不能去 HttpHeaderInspectingAuthenticatorConfigurationElement -> BasicAuthenticationHeaderInspectorConfigurationElement，因此通过将参数转换为 dynamic，您告诉 DLR 参数类型是在运行时确定的。