VBA从一年中的周数获取开始日期

Question

我想检索一周的第一天的日期（一周从星期一开始）知道年份和周数。（1年52周）

Dim nYear As Integer, _
    nWeek, As Integer
    startDate As Date

    nYear = 2018
    nWeek= 1


'startDate = ?

预期结果 ：01/01/2018

有没有一种简单而动态的方法来做到这一点？

谢谢

Answer 1

Dim nTrimester As Integer, _
    nYear As Integer, _
    nWeek As Integer, _
    wd As Integer, _
    startDate As Date, _
    inputDate As Date

nYear = 2019
nWeek = 1    

inputDate = DateSerial(nYear, 1, 1)
inputDate = DateAdd("ww", nWeek - 1, inputDate)
wd = Weekday(inputDate, vbMonday)   

startDate = DateAdd("d", 1 - wd, inputDate)

编辑：上面的答案将一年中的第一周视为一年中第一天的那一周。根据 ISO 8601，一年的第一周是一年中的第一个星期四，因此，应该是

Dim nTrimester As Integer, _
    nYear As Integer, _
    nWeek As Integer, _
    wd As Integer, _
    startDate As Date, _
    inputDate As Date

nYear = 2021
nWeek = 1

inputDate = DateSerial(nYear, 1, 1)

If Weekday(inputDate, vbMonday) > 4 Then
    nWeek = nWeek + 1
End If
    
inputDate = DateAdd("ww", nWeek - 1, inputDate)
wd = Weekday(inputDate, vbMonday)

startDate = DateAdd("d", 1 - wd, inputDate)

两种方法的区别在于，第一种方法是2021年第一周的第一天是2020-12-28，第二种方法是2021-01-04