我正在开发一个测试程序，该程序可以帮助我弄清楚 Microsoft.Practices.EnterpriseLibrary.ExceptionHandling 框架是如何工作的。该程序定义了几种自定义异常类型并将自定义异常处理程序与每种类型相关联。在运行时，程序提示用户抛出异常的类型，抛出异常，并使用 ExceptionHandling 框架为异常类型调用适当的异常处理程序：
using System;
using System.Collections.Specialized;
using Microsoft.Practices.EnterpriseLibrary.Common.Configuration;
using Microsoft.Practices.EnterpriseLibrary.ExceptionHandling;
using Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.Configuration;
namespace ConsoleApplication1
{
public class AException : Exception { public AException(string message) : base(message) { } }
public class BException : Exception { public BException(string message) : base(message) { } }
public class BBException : BException { public BBException(string message) : base(message) { } }
public class WrapperException : Exception
{
public WrapperException(Exception innerException)
: base("Wrapped exception: [" + innerException.Message + "]", innerException) { }
}
public class MyExceptionHandler<T> : IExceptionHandler
{
protected NameValueCollection Ignore { get; set; }
public MyExceptionHandler(NameValueCollection ignore)
{
Ignore = ignore;
}
#region IExceptionHandler Members
public virtual Exception HandleException(Exception exception, Guid handlingInstanceId)
{
if (exception is T)
{
Console.WriteLine("Exception Handled:");
Console.WriteLine(" Expected Type : [{0}]", typeof(T).ToString());
Console.WriteLine(" Actual Type : [{0}]", exception.GetType().ToString());
Console.WriteLine(" Message : [{0}]", exception.Message);
Console.WriteLine();
}
else
{
Console.WriteLine("Unexpected Exception Type: [{0}]", exception.GetType().ToString());
}
return exception;
}
#endregion
}
[ConfigurationElementType(typeof(CustomHandlerData))]
public class AExceptionHandler : MyExceptionHandler<AException>
{
public AExceptionHandler(NameValueCollection ignore) : base(ignore) { }
}
[ConfigurationElementType(typeof(CustomHandlerData))]
public class BExceptionHandler : MyExceptionHandler<BException>
{
public BExceptionHandler(NameValueCollection ignore) : base(ignore) { }
}
[ConfigurationElementType(typeof(CustomHandlerData))]
public class ExceptionHandler : MyExceptionHandler<Exception>
{
public ExceptionHandler(NameValueCollection ignore) : base(ignore) { }
public override Exception HandleException(Exception exception, Guid handlingInstanceId)
{
var wrapper = new WrapperException(exception);
return base.HandleException(wrapper, handlingInstanceId);
}
}
class Program
{
static void ThrowSomething()
{
Console.Write("Enter the exception type: ");
var x = Console.ReadLine();
if (x.Equals("a"))
{
throw new AException(x);
}
else if (x.Equals("b"))
{
throw new BException(x);
}
else if (x.Equals("bb"))
{
throw new BBException(x);
}
else
{
throw new Exception(x);
}
}
static void Main(string[] args)
{
ExceptionManager xm = EnterpriseLibraryContainer.Current.GetInstance<ExceptionManager>();
while (true)
{
//xm.Process(ThrowSomething, "Policy");
try
{
ThrowSomething();
}
catch(Exception ex)
{
Exception exToThrow = null;
if (ExceptionPolicy.HandleException(ex, "policy", out exToThrow))
{
if (exToThrow == null)
{
throw;
}
else
{
throw exToThrow;
}
}
}
Console.WriteLine();
}
}
}
}
在该程序的第一次迭代中，我使用 ExceptionManager.Process() 方法来调用我的 ThrowSomething() 方法。使用这种方法，一切都很好。然后我修改了 Main 以使用 ExceptionPolicy.HandleException() 代替。当我这样做时，我开始收到此异常：
未处理的异常：Microsoft.Practices.ServiceLocation.ActivationException：尝试获取 ExceptionPolicyImpl 类型的实例时发生激活错误，键“策略”---> Microsoft.Practices.Unity.ResolutionFailedException：依赖项解析失败，类型 =“Microsoft. Practices.EnterpriseLibrary.ExceptionHandling.ExceptionPolicyImpl”，名称 = “策略”。异常发生时：解决时。例外是： InvalidOperationException - ExceptionPolicyImpl 类型有多个长度为 2 的构造函数。无法消除歧义。
我的 App.config 文件包含以下内容：
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<configSections>
<section name="exceptionHandling" type="Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.Configuration.ExceptionHandlingSettings, Microsoft.Practices.EnterpriseLibrary.ExceptionHandling, Version=5.0.414.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" requirePermission="true" />
</configSections>
<exceptionHandling>
<exceptionPolicies>
<add name="Policy">
<exceptionTypes>
<add name="AException" type="ConsoleApplication1.AException, ConsoleApplication1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"
postHandlingAction="None">
<exceptionHandlers>
<add type="ConsoleApplication1.AExceptionHandler, ConsoleApplication1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"
name="AExceptionHandler" />
</exceptionHandlers>
</add>
<add name="BException" type="ConsoleApplication1.BException, ConsoleApplication1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"
postHandlingAction="None">
<exceptionHandlers>
<add type="ConsoleApplication1.BExceptionHandler, ConsoleApplication1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"
name="BExceptionHandler" />
</exceptionHandlers>
</add>
<add name="All Other Exceptions" type="System.Exception, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
postHandlingAction="NotifyRethrow">
<exceptionHandlers>
<add type="ConsoleApplication1.ExceptionHandler, ConsoleApplication1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"
name="ExceptionHandler" />
</exceptionHandlers>
</add>
</exceptionTypes>
</add>
</exceptionPolicies>
</exceptionHandling>
</configuration>
谁能告诉我为什么会出现此异常以及如何解决该问题？