LINQ orderby on date字段降序

Question

如何在下面的代碼中更改LINQ查詢以按降序排序（最新的第一個，最早的最後一個）？

using System; 
using System.Linq; 
using System.Collections.Generic; 


namespace Helloworld 
{ 
    class MainClass 
    { 
     public static void Main (string[] args) 
     { 
      List<Envelops> env = new List<Envelops>(); 
      Envelops e = new Envelops { ReportDate = DateTime.Now }; 
      env.Add (e); 
      e = new Envelops { ReportDate = DateTime.Now.AddDays (5) }; 
      env.Add (e); 
      e = new Envelops { ReportDate = new DateTime (2011, 3, 3) }; 
      env.Add (e); 
      e = new Envelops { ReportDate = DateTime.Now }; 
      env.Add (e); 

      foreach (Envelops r in env) { 
       Console.WriteLine ( r.ReportDate.ToString("yyyy-MMM")); 
      } 

      var ud = (from d in env     
       select d.ReportDate.ToString("yyyy-MMM")).Distinct();  

      Console.WriteLine ("After distinct"); 

      foreach (var r in ud) { 
       Console.WriteLine (r); 
      } 

     } 
    } 

    class Envelops 
    { 
     public DateTime ReportDate { get; set; } 
    } 

}`enter code here` 

電流輸出：

2011-Apr 
2011-May 
2011-Mar 
2011-Apr 
After distinct 
2011-Apr 
2011-May 
2011-Mar 

我要在以下順序輸出：

may 
april 
march order 

Answer 1

我不相信鮮明（）保證維持集合的順序。

嘗試拉出一個匿名類型第一和獨特/排序上，你轉換爲字符串之前：

var ud = env.Select(d => new 
         { 
          d.ReportDate.Year, 
          d.ReportDate.Month, 
          FormattedDate = d.ReportDate.ToString("yyyy-MMM") 
         }) 
      .Distinct() 
      .OrderByDescending(d => d.Year) 
      .ThenByDescending(d => d.Month) 
      .Select(d => d.FormattedDate); 

Answer 2

env.OrderByDescending(x => x.ReportDate)

Answer 3

這種說法一定會幫你的，

`ENV = env.OrderByDescending（ c => c.ReportDate）.ToList（）;