moment.js方便了javascript中日期的计算，所以我也写这些函数方便vb.net中日期的计算。
求今年的最后一天的23:59:59，这个月的最后一天等等。
Function EndOf(Unit As String) As Date
Dim mydate As Date = Now()
Dim myyear As Integer = Year(mydate)
Dim mymonth As Integer = Month(mydate)
Dim myday As Integer = Day(mydate)
Dim myhour As Integer = Hour(mydate)
Dim myminute As Integer = Minute(mydate)
Dim mysecond As Integer = Second(mydate)
Select Case Unit
Case "year"
Console.WriteLine("year")
EndOf = New Date(myyear, 12, 31, 23, 59, 59)
Case "month"
Console.WriteLine("month")
Dim NextMonth As Date = DateAdd(DateInterval.Month, 1, mydate)
Dim Date2 As Date = DateAdd(DateInterval.Day, -1, setDay(1, NextMonth))
Dim myyear2 As Integer = Year(Date2)
Dim mymonth2 As Integer = Month(Date2)
Dim myday2 As Integer = Day(Date2)
EndOf = New Date(myyear2, mymonth2, myday2, 23, 59, 59)
Case "week"
Dim Date1 = DateAdd(DateInterval.Day, 6, StartOf("week"))
Dim myyear1 As Integer = Year(Date1)
Dim mymonth1 As Integer = Month(Date1)
Dim myday1 As Integer = Day(Date1)
EndOf = New Date(myyear1, mymonth1, myday1, 23, 59, 59)
Case "day"
EndOf = New Date(myyear, mymonth, myday, 23, 59, 59)
Case "hour"
EndOf = New Date(myyear, mymonth, myday, myhour, 59, 59)
Case "minute"
EndOf = New Date(myyear, mymonth, myday, myhour, myminute, 59)
End Select
End Function
EndOf("year")
EndOf("month")
EndOf("week")
EndOf("day")
EndOf("hour")
EndOf("minute")
这个月有多少天？
Function DaysInMonth() As Integer
Dim lastDay As Date = EndOf("month")
DaysInMonth = Day(lastDay)
End Function
Date1是否在Date2之前？
Function IsBefore(Date1 As Date, Date2 As Date) As Boolean
IsBefore = DateDiff(DateInterval.Second, Date1, Date2) > 0
End Function
两个日期是否相等？
Function IsSame(Date1 As Date, Date2 As Date) As Boolean
IsSame = DateDiff(DateInterval.Second, Date1, Date2) = 0
End Function
Date1是否在Date2之后？
Function IsAfter(Date1 As Date, Date2 As Date) As Boolean
IsAfter = DateDiff(DateInterval.Second, Date1, Date2) < 0
End Function
Date1是否小于或等于Date2？
Function IsSameOrBefore(Date1 As Date, Date2 As Date) As Boolean
IsSameOrBefore = IsSame(Date1, Date2) Or IsBefore(Date1, Date2)
End Function
Target是否在Date1和Date2之间？
Function IsBetween(Target As Date, Date1 As Date, Date2 As Date)
IsBetween = IsSameOrAfter(Target, Date1) And IsSameOrBefore(Target, Date2)
End Function
判断是否是闰年？
Function IsLeapYear(MyDate As Date) As Boolean
Dim YearNum As Integer = Year(MyDate)
Dim Result As Boolean
If (YearNum Mod 4 = 0 And YearNum Mod 100 <> 0) Or YearNum Mod 400 = 0 Then
Result = True
Else
Result = False
End If
IsLeapYear = Result
End Function
