设计原则：消除Switch...Case的过程，可能有点过度设计了。

备注

不要重复自己，也不要重复别人，一旦养成了“拷贝和粘贴”的习惯，写程序的时候非常容易导致重复，好在一直暗示自己要稍后进行重构，本文给出一个重构的示例。

需求

需求：按照年、月和日显示销售数据，根据不同的周期类型，有三个问题需要注意：

1. 默认的日期范围不同
2. 图表中显示的格式不同
3. 默认的模拟数据不同（发布环境会使用真实的数据）

如下图：

第一遍代码（重复的代码）

最爱的拷贝和粘贴。

默认的日期范围不同

         private void ResetStartDateAndEndDate()
         {
             this.EndDate = DateTime.Now;

             switch (_currentCircle)
             {
                 case "日":
                     this.StartDate = this.EndDate.AddMonths(-);
                     break;
                 case "月":
                     this.StartDate = this.EndDate.AddMonths(-);
                     break;
                 case "年":
                     this.StartDate = this.EndDate.AddMonths(- * );
                     break;
             }

             this.StartDate = this.StartDate.AddDays();
         }

图表中显示的格式不同

         public string DisplayDate
         {
             get
             {
                 switch (this.Cycle)
                 {
                     case "日":
                         return this.Date.ToString("yyyy-MM-dd");
                     case "月":
                         return this.Date.ToString("yyyy-MM");
                     case "年":
                         return this.Date.ToString("yyyy");
                     default:
                         throw new InvalidOperationException("周期类型不匹配");
                 }
             }
         }

默认的模拟数据不同

         public IEnumerable<SalesViewModel> Find(string cycle, DateTime startDate, DateTime endDate)
         {
             switch (cycle)
             {
                 case "日":
                     return new List<SalesViewModel>
                     {
                         new SalesViewModel{ Date = DateTime.Now.AddDays(-).AddDays(), Total = , Cycle = cycle },
                         new SalesViewModel{ Date = DateTime.Now, Total = , Cycle = cycle }
                     };
                 case "月":
                     return new List<SalesViewModel>
                     {
                         new SalesViewModel{ Date = DateTime.Now.AddMonths(-).AddDays(), Total = , Cycle = cycle },
                         new SalesViewModel{ Date = DateTime.Now, Total = , Cycle = cycle }
                     };
                 case "年":
                     return new List<SalesViewModel>
                     {
                         new SalesViewModel{ Date = DateTime.Now.AddYears(-).AddDays(), Total = , Cycle = cycle },
                         new SalesViewModel{ Date = DateTime.Now, Total = , Cycle = cycle }
                     };
                 default:
                     return new List<SalesViewModel>();
             }
         }

第二遍代码（消除重复）

“门面类型+多态+私有内部类”消除重复

 using System;
 using System.Net;
 using System.Windows;
 using System.Windows.Controls;
 using System.Windows.Documents;
 using System.Windows.Ink;
 using System.Windows.Input;
 using System.Windows.Media;
 using System.Windows.Media.Animation;
 using System.Windows.Shapes;
 using System.Collections.Generic;

 namespace Marking.Dashboard.Infrastructures
 {
     public static class CycleTypeHelper
     {
         private static Dictionary<string, CycleType> _CycleTypeMaps = new Dictionary<string, CycleType>
         {
             { "日", new DayCycleType() },
             { "月", new MonthCycleType() },
             { "年", new YearCycleType() }
         };

         public static IEnumerable<string> CircleTypes
         {
             get
             {
                 return _CycleTypeMaps.Keys;
             }
         }

         public static DateTime GetDefaultStartDate(string cycleType, DateTime endDate)
         {
             return _CycleTypeMaps[cycleType].GetDefaultStartDate(endDate);
         }

         public static string GetDisplayDateString(string cycleType, DateTime date)
         {
             return _CycleTypeMaps[cycleType].GetDisplayDateString(date);
         }

         public static IEnumerable<DateTime> SimulateDates(string cycleType, DateTime startDate, DateTime endDate)
         {
             return _CycleTypeMaps[cycleType].SimulateDates(startDate, endDate);
         }

         private abstract class CycleType
         {
             public abstract DateTime GetDefaultStartDate(DateTime endDate);

             public abstract string GetDisplayDateString(DateTime date);

             public abstract IEnumerable<DateTime> SimulateDates(DateTime startDate, DateTime endDate);
         }

         private class YearCycleType : CycleType
         {
             public override DateTime GetDefaultStartDate(DateTime endDate)
             {
                 return endDate.AddMonths(- * );
             }

             public override string GetDisplayDateString(DateTime date)
             {
                 return date.ToString("yyyy");
             }

             public override IEnumerable<DateTime> SimulateDates(DateTime startDate, DateTime endDate)
             {
                 for (var i = startDate; i <= endDate; i = i.AddYears())
                 {
                     yield return i;
                 }
             }
         }

         private class MonthCycleType : CycleType
         {
             public override DateTime GetDefaultStartDate(DateTime endDate)
             {
                 return endDate.AddMonths(-);
             }

             public override string GetDisplayDateString(DateTime date)
             {
                 return date.ToString("yyyy-MM");
             }

             public override IEnumerable<DateTime> SimulateDates(DateTime startDate, DateTime endDate)
             {
                 for (var i = startDate; i <= endDate; i = i.AddMonths())
                 {
                     yield return i;
                 }
             }
         }

         private class DayCycleType : CycleType
         {
             public override DateTime GetDefaultStartDate(DateTime endDate)
             {
                 return endDate.AddMonths(-);
             }

             public override string GetDisplayDateString(DateTime date)
             {
                 return date.ToString("MM-dd");
             }

             public override IEnumerable<DateTime> SimulateDates(DateTime startDate, DateTime endDate)
             {
                 for (var i = startDate; i <= endDate; i = i.AddDays())
                 {
                     yield return i;
                 }
             }
         }
     }
 }

备注

完成第一遍后，差点不想进行重构了，战胜自己非常不容易，继续努力。