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();
}
CustomFormat.rar