c# - 反射:Property-GetValue by Class-Type(因此没有实例化的对象)

Question

在我们的项目中，我们有多个所谓的Projections。这些 Projection 类都有一个带有 get 的字符串属性，称为 ProjectionTypeName。此 ProjectionTypeName 对于所有投影应该是唯一的。

今天我遇到了两个投影具有相同 ProjectionTypeName 的问题，这造成了很多麻烦。所以我决定进行单元测试以防止这种情况再次发生。

我使用以下方法获取所有 Projections 的所有 Types:

// The excluded abstract projections
private static readonly List<Type> AbstractProjections = new List<Type>
{
    typeof(AbstractRavenDbChangesProjection),
    typeof(AbstractRavenDbTimelineProjection)
};

private static IEnumerable<Type> GetAllProjectionTypes()
{
    return typeof(AbstractRavenDbChangesProjection)
        .Assembly
        .GetTypes()
        .Where(x => typeof(AbstractRavenDbChangesProjection).IsAssignableFrom(x) && !x.IsInterface)
        .Except(AbstractProjections)
        .ToList();
}

然后我进行了实际测试:

[Test]
public void TestNoDuplicated()
{
    var noDuplicatedList = new Dictionary<Type, string>();
    var projectionTypes = GetAllProjectionTypes();
    foreach (var type in projectionTypes)
    {
        // TODO: Get projectionTypeName-value by Projection's Type
        var projectionTypeName = ??;

        Assert.IsFalse(noDuplicatedList.ContainsValue(projectionTypeName),
            "{0} has been found as ProjectionTypeName in two different Projections: {1} & {2}",
                projectionTypeName,
                noDuplicatedList.First(x => x.Value == projectionTypeName).Key,
                type);
            noDuplicatedList.Add(type, projectionTypeName);
    }   
}

我四处看了看，甚至尝试了 a piece of code by @JohnSkeet ，即使他说(我引用):

Please don't do this. Ever. It's ghastly. It should be trampled on, cut up into little bits, set on fire, then cut up again. Fun though, isn't it? ;)

但自 2012 年(发布答案时)以来，这似乎已经发生了变化，现在当您尝试这种反射时，.NET 会给出错误:"System.Security.VerificationException : Operation could destabilize the runtime ”。

所以，我的问题。当我只有类的 Type 可供我使用(而不是实际实例化的对象)时，如何获取字符串属性 ProjectionTypeName 的值。

如果我有一个实例化的对象，我将能够做这样的事情:

myInstantiatedObject.GetType().GetProperty("ProjectionTypeName")
    .GetValue(myInstantiatedObject, null);

Answer 1

改用自定义属性怎么样？

[AttributeUsage(System.AttributeTargets.Class)]
public sealed class ProjectionTypeNameAttribute : Attribute
{
  private string m_Name;

  public string Name
  {
    get { return m_Name; }
  }

  public ProjectionTypeNameAttribute(string name)
  {
    m_Name = name;
  }
}

[ProjectionTypeNameAttribute(ProjectionWhatever.PROJECTION_NAME)]
public class ProjectionWhatever
{
  public const string PROJECTION_NAME = "Whatever";

  // if you want to have property as well
  public string ProjectionTypeName
  {
    get
    {
      return PROJECTION_NAME;
    }
  }
}   

// query if type has attribute
var type = typeof(ProjectionWhatever);
var attributes = type.GetCustomAttributes(typeof(ProjectionTypeNameAttribute), false);
if (attributes != null && attributes.Length > 0)
{
  var attribute = (ProjectionTypeNameAttribute)attributes[0];
  // use attribute.Name
}