输出自定义日期格式

通过实现IFormatProvider, ICustomFormatter接口可以实现自定义的格式输现，这里有实现一个例子，以输出日期格式为例(显示今天、明天、后天和"x月x日"等)

1、假设我们有多种显示日期格式的需求，我们可以定义一个枚举如下：

     public   enum  DateTimeFormat
    {
        WithDayName, // 含"前天、昨天、今天、明天、后天的显示"
        WithWeek // 含星期几的显示
    }

 

2、每种类型实现 IFormatProvider, ICustomFormatter接口。

internal   class  WithDayNameFormat : IFormatProvider, ICustomFormatter
    {
         public   object  GetFormat(Type formatType)
        {
             if  (formatType  ==   typeof (ICustomFormatter))
            {
                 return   this ;
            }
             else
            {
                 return  Thread.CurrentThread.CurrentCulture.GetFormat(formatType);
            }
        }

         public   string  Format( string  format,  object  arg, IFormatProvider formatProvider)
        {
             string  str;
            IFormattable formatable  =  arg  as  IFormattable;
             if  (formatable  ==   null )
            {   str  =  arg.ToString();}
             else
            {
                str  =  formatable.ToString(format, formatProvider);
            }
             if  (arg.GetType()  ==   typeof (DateTime))
            {
                DateTime dt  =  (DateTime)arg;
                 int  days  =  (DateTime.Now  -  dt).Days;
                 switch (days)
                {
                     case   - 2 :
                        str = " 前天 " ;
                         break ;
                     case   - 1 :
                        str  =   " 明天 " ;
                         break ;
                     case   0 :
                        str  =   " 今天 " ;
                         break ;
                     case   1 :
                        str  =   " 明天 " ;
                         break ;
                     case   2 :
                        str  =   " 后天 " ;
                         break ;
                     default :
                        str  =   string .Format( " {0}月{1}日 " , dt.Month, dt.Day);
                         break ;
                }
            }
             return  str;
        }

    }

 

internal   class  WithWeekFormat : IFormatProvider, ICustomFormatter
    {
         public   object  GetFormat(Type formatType)
        {
             if  (formatType  ==   typeof (ICustomFormatter))
            {
                 return   this ;
            }
             else
            {
                 return  Thread.CurrentThread.CurrentCulture.GetFormat(formatType);
            }
        }

         public   string  Format( string  format,  object  arg, IFormatProvider formatProvider)
        {
             string  str;
            IFormattable formatable  =  arg  as  IFormattable;
             if  (formatable  ==   null )
            { str  =  arg.ToString(); }
             else
            {
                str  =  formatable.ToString(format, formatProvider);
            }
             if  (arg.GetType()  ==   typeof (DateTime))
            {
                DateTime dt  =  (DateTime)arg;
                 string  dayOfWeef  =  dt.DayOfWeek.ToString().Trim();
                 switch  (dayOfWeef)
                {
                     case   " Monday " :
                        dayOfWeef  =   " 一 " ;
                         break ;
                     case   " Tuesday " :
                        dayOfWeef  =   " 二 " ;
                         break ;
                     case   " Wednesday " :
                        dayOfWeef  =   " 三 " ;
                         break ;
                     case   " Thursday " :
                        dayOfWeef  =   " 四 " ;
                         break ;
                     case   " Friday " :
                        dayOfWeef  =   " 五 " ;
                         break ;
                     case   " Saturday " :
                        dayOfWeef  =   " 六 " ;
                         break ;
                     case   " Sunday " :
                        dayOfWeef  =   " 日 " ;
                         break ;
                }
                 return   string .Format( " {0}年{1}月{2}日 星期{3} " , dt.Year, dt.Month, dt.Day, dayOfWeef);
            }
             return  str;
        }
    }

3、使用扩展方法对使用进行封装

     public   static   class  DateTimeExtention
    {
         public   static   string  ToCustomFormat( this  DateTime dt, DateTimeFormat format)
        {
             string  str;
             switch  (format)
            {
                 case  DateTimeFormat.WithDayName:
                    str  =   string .Format( new  WithDayNameFormat(),  " {0} " , dt);
                     break ;
                 case  DateTimeFormat.WithWeek:
                      str  =   string .Format( new  WithWeekFormat(),  " {0} " , dt);
                       break ;
                 default :
                     throw   new  NotSupportedException( " 不支持的日期格式类型DateTimeFormat " );
                     break ;
            }
             return  str;
        }
    }

 

4、客户端使用：

 

 

         static   void  Main( string [] args)
        {
            Console.WriteLine(DateTime.Now.AddDays( - 3 ).ToCustomFormat(DateTimeFormat.WithDayName));
            Console.WriteLine(DateTime.Now.AddDays( - 2 ).ToCustomFormat(DateTimeFormat.WithDayName));
            Console.WriteLine(DateTime.Now.AddDays( - 1 ).ToCustomFormat(DateTimeFormat.WithDayName));
            Console.WriteLine(DateTime.Now.AddDays( 0 ).ToCustomFormat(DateTimeFormat.WithDayName));
            Console.WriteLine(DateTime.Now.AddDays( 1 ).ToCustomFormat(DateTimeFormat.WithDayName));
            Console.WriteLine(DateTime.Now.AddDays( 2 ).ToCustomFormat(DateTimeFormat.WithDayName));
            Console.WriteLine(DateTime.Now.AddDays( 3 ).ToCustomFormat(DateTimeFormat.WithDayName));

            Console.WriteLine(DateTime.Now.AddDays( - 3 ).ToCustomFormat(DateTimeFormat.WithWeek));
            Console.WriteLine(DateTime.Now.AddDays( - 2 ).ToCustomFormat(DateTimeFormat.WithWeek));
            Console.WriteLine(DateTime.Now.AddDays( - 1 ).ToCustomFormat(DateTimeFormat.WithWeek));
            Console.WriteLine(DateTime.Now.AddDays( 0 ).ToCustomFormat(DateTimeFormat.WithWeek));
            Console.WriteLine(DateTime.Now.AddDays( 1 ).ToCustomFormat(DateTimeFormat.WithWeek));
            Console.WriteLine(DateTime.Now.AddDays( 2 ).ToCustomFormat(DateTimeFormat.WithWeek));
            Console.WriteLine(DateTime.Now.AddDays( 3 ).ToCustomFormat(DateTimeFormat.WithWeek));

            Console.ReadKey();
        }