选择具有特定属性值的属性

Question

我正在寻找一种方法来选择在单个LINQ语句中具有特定值的特定自定义属性的属性。

我得到的属性，我想要的属性，但我不知道如何选择其特定的值。

<AttributeUsage(AttributeTargets.Property)> 
Public Class PropertyIsMailHeaderParamAttribute 
    Inherits System.Attribute 

    Public Property HeaderAttribute As String = Nothing 
    Public Property Type As ParamType = Nothing 

    Public Sub New() 

    End Sub 

    Public Sub New(ByVal headerAttribute As String, ByVal type As ParamType) 
     Me.HeaderAttribute = headerAttribute 
     Me.Type = type 
    End Sub 

    Public Enum ParamType 
     base = 1 
     open 
     closed 
    End Enum 
    End Class 


    private MsgData setBaseProperties(MimeMessage mailItem, string fileName) 
    { 
     var msgData = new MsgData(); 
     Type type = msgData.GetType(); 
     var props = from p in this.GetType().GetProperties() 
        let attr = p.GetCustomAttributes(typeof(Business.IT._21c.AddonFW.PropertyIsMailHeaderAttribute), true) 
        where attr.Length == 1 
        select new { Property = p, Attribute = attr.FirstOrDefault() as Business.IT._21c.AddonFW.PropertyIsMailHeaderAttribute }; 
    } 

[解决方法]

var baseProps = from p in this.GetType().GetProperties() 
       let attr = p.GetCustomAttribute<PropertyIsMailHeaderParamAttribute>() 
       where attr != null && attr.Type == PropertyIsMailHeaderParamAttribute.ParamType.@base 
select new { Property = p, Attribute = attr as Business.IT._21c.AddonFW.PropertyIsMailHeaderParamAttribute }; 

Answer 1

您可能已投下Attribute对象（使用使用OfType<>扩展名的常规演员或通过例如）你的类型，但最简单的方法是使用通用版本GetCustomAttribute<>：

var props = from p in this.GetType().GetProperties() 
      let attr = p.GetCustomAttribute<PropertyIsMailHeaderAttribute>() 
      where attr != null && attr.HeaderAttribute == "FooBar" 
           && attr.Type = ParamType.open 
      select whatever;