c# - 创建 SqlCeLockTimeoutException 的实例

Question

出于单元测试目的，我想创建一个类型为 SqlCeLockTimeoutException 的模拟对象

因为它的构造函数是 protected ，所以我在测试中创建了一个扩展类:

[Serializable]
private class TestableSqlCeLockTimeoutException : SqlCeLockTimeoutException
{
    public TestableSqlCeLockTimeoutException()
           : this(new SerializationInfo(typeof (TestableSqlCeLockTimeoutException), 
                                        new FormatterConverter()), 
                  new StreamingContext())
    {
    }

    protected TestableSqlCeLockTimeoutException(SerializationInfo info,
                                                StreamingContext context) 
           : base(info, context)
    {
    }
}

但是，我在创建实例时不断收到以下异常:

Test method Foo threw exception:
System.Runtime.Serialization.SerializationException: Member 'ClassName' was not found.

为什么我总是收到它？我尝试使用 Serializable 属性但无济于事。

任何解决方法也会有所帮助。

Answer 1

@Mugan 你问了一个非常有趣的问题!为了回答这个问题，我不得不反编译 SqlCeLockTimeoutException。当我试图帮助你时，我学到了很多东西。谢谢。

出现问题是因为 System.Exception C`tor 需要反序列化一些属性:

[System.Security.SecuritySafeCritical]  // auto-generated
protected Exception(SerializationInfo info, StreamingContext context) 
{
 //some validation
    _className = info.GetString("ClassName");
    _message = info.GetString("Message");
    _data = (IDictionary)(info.GetValueNoThrow("Data",typeof(IDictionary)));
    _innerException = (Exception)(info.GetValue("InnerException",typeof(Exception)));
    _helpURL = info.GetString("HelpURL");
    _stackTraceString = info.GetString("StackTraceString");
    _remoteStackTraceString = info.GetString("RemoteStackTraceString");
    _remoteStackIndex = info.GetInt32("RemoteStackIndex");
    _exceptionMethodString = (String)(info.GetValue("ExceptionMethod",typeof(String)));
    HResult = info.GetInt32("HResult");
    _source = info.GetString("Source");
//some bla bla....

为了解决上面的问题我把protected C`tor改成了public然后使用:

var info = new SerializationInfo(typeof (TestableSqlCeLockTimeoutException), 
           new FormatterConverter());
info.AddValue("ClassName", string.Empty);
info.AddValue("Message", string.Empty);
info.AddValue("InnerException", new ArgumentException());
info.AddValue("HelpURL", string.Empty);
info.AddValue("StackTraceString", string.Empty);
info.AddValue("RemoteStackTraceString", string.Empty);
info.AddValue("RemoteStackIndex", 0);
info.AddValue("ExceptionMethod", string.Empty);
info.AddValue("HResult", 1);
info.AddValue("Source", string.Empty);
new TestableSqlCeLockTimeoutException(info,new StreamingContext());

然后这次从 SqlCeException 引发了新的异常。 SqlCeException Ctor还需要一个属性__Errors__:

protected SqlCeException(SerializationInfo info, StreamingContext context)
  : base(info, context)
{
  if (info == null)
    throw new ArgumentNullException("info");
  this.Errors = (SqlCeErrorCollection) info.GetValue("__Errors__", typeof (SqlCeErrorCollection));
}

SqlCeErrorCollection Ctor 是内部的，因此我使用了 Reflaction 来创建一个实例:

BindingFlags flags = BindingFlags.NonPublic | BindingFlags.Instance;
CultureInfo culture = null; // use InvariantCulture or other if you prefer
object instantiatedType =
       Activator.CreateInstance(typeof(SqlCeErrorCollection), flags, null, null, culture);
info.AddValue("__Errors__", instantiatedType);

现在一切正常。我最终得到了一个创建方法:

private static SqlCeLockTimeoutException CreateSqlCeLockTimeoutExceptionForTest()
{
    var info = new SerializationInfo(typeof (TestableSqlCeLockTimeoutException), 
               new FormatterConverter());
    info.AddValue("ClassName", string.Empty);
    info.AddValue("Message", string.Empty);
    info.AddValue("InnerException", new ArgumentException());
    info.AddValue("HelpURL", string.Empty);
    info.AddValue("StackTraceString", string.Empty);
    info.AddValue("RemoteStackTraceString", string.Empty);
    info.AddValue("RemoteStackIndex", 0);
    info.AddValue("ExceptionMethod", string.Empty);
    info.AddValue("HResult", 1);
    info.AddValue("Source", string.Empty);
    BindingFlags flags = BindingFlags.NonPublic | BindingFlags.Instance;
    CultureInfo culture = null; // use InvariantCulture or other if you prefer
    object instantiatedType = Activator.CreateInstance(typeof (SqlCeErrorCollection), 
                                flags, null, null, culture);
    info.AddValue("__Errors__", instantiatedType);
    return new TestableSqlCeLockTimeoutException(info, new StreamingContext());
}

您还可以使用 Reflaction 创建 SqlCeLockTimeoutException 的新实例，而不是 TestableSqlCeLockTimeoutException:

private static SqlCeLockTimeoutException CreateSqlCeLockTimeoutExceptionForTest()
{
    BindingFlags flags = BindingFlags.NonPublic | BindingFlags.Instance;
    CultureInfo culture = null; // use InvariantCulture or other if you prefer
    object instantiatedType = Activator.CreateInstance(typeof (SqlCeErrorCollection), 
                  flags, null, null, culture);

    object result = Activator.CreateInstance(typeof(SqlCeLockTimeoutException), 
                  flags, null, new []{instantiatedType}, culture);

    return (SqlCeLockTimeoutException)result;
}