如何获取嵌入在自定义属性中的类型？

Question

我有几个包含各种属性的类。这里有一个例子：

[XmlInclude(typeof(AFReader))] 
[XmlInclude(typeof(SQLReader))] 
[XmlInclude(typeof(MySQLReader))] 
[Serializable] 
[DataContract] 
public class DataSource  
{ 
    ...      
} 

我需要能够通过这些属性来过滤和选择其BaseType的是，在这里它继承（DataSource在这种情况下）的类型。

所以最后，我想是这样的：

static private List<Type> AttributeFilter(IEnumerable<Attribute> attributes, Type baseType) 
    { 
     List<Type> filteredAttributes = new List<Type>(); 
     foreach (Attribute at in attributes) 
     { 

      // if (at.TypeId.GetType().BaseType == baseType) 
      //  filteredAttributes.Add(at.GetType()); 

      // if (at.GetType().BaseType == baseType) 
      //  filteredAttributes.Add(at.GetType()); 

     } 

     return filteredAttributes; 
    } 

与调用：

  Type test = typeof(DataSource); 

      IEnumerable<Attribute> customAttributes = test.GetCustomAttributes(); 
      List<Type> filteredAttributes = AttributeFilter(customAttributes, test); 

Answer 1

首先，你要，我试过

List<Type> filteredAttributes = {typeof(AFReader), typeof(SQLReader), typeof(MySQLReader)}; 

//List<MemberInfo> .. would work as well 

事将您的属性限制为XmlIncludeAttribute。然后，您可以检查属性'Type属性。所以，你的函数如下所示：

static private List<Type> AttributeFilter(IEnumerable<XmlIncludeAttribute> attributes, Type baseType) 
{ 
    List<Type> filteredAttributes = new List<Type>(); 
    foreach (XmlIncludeAttribute at in attributes) 
    { 
     if (at.Type.BaseType == baseType) 
     { 
      filteredAttributes.Add(at.Type); 
     } 
    } 
    return filteredAttributes; 
} 

你可以这样调用：

IEnumerable<XmlIncludeAttribute> customAttributes = test.GetCustomAttributes().Where(x => x is XmlIncludeAttribute).Select(x => x as XmlIncludeAttribute); 
List<Type> filteredAttributes = AttributeFilter(customAttributes, test); 

Answer 2

您的代码看属性本身的Type通过调用GetType()，而不是Type简称由它的构造函数中的属性。尝试是这样的：

public static IEnumerable<Type> GetXmlIncludeTypes(Type type) { 
    foreach (var attr in Attribute.GetCustomAttributes(type)) { 
     if (attr is XmlIncludeAttribute) { 
      yield return ((XmlIncludeAttribute)attr).Type; 
     } 
    } 
} 

你会这样称呼它：

foreach (var t in GetXmlIncludeTypes(typeof(Foo))) { 
    //whatever logic you are looking for in the base types 
}