Question

I am developing an ASPX VB.NET file. My assignment is to convert an integer representing week of the year into that end date. For example, if user selects Week 4 for 2011, I want to get date = 1/22/11. How do I do this in VB.NET?

Answer 1

I’ve asked a similar question a short while ago. I also have an answer from J.Skeet for a RegularExpressionValidator(if you need one).

Here is what i have to get a date from a week of year:

Public Shared Function FirstDateOfWeek(ByVal year As Integer, ByVal weekOfYear As Integer) As DateTime
      Dim jan1 As New DateTime(year, 1, 1)
      Dim daysOffset As Integer = CInt(Globalization.CultureInfo.CurrentCulture.DateTimeFormat.FirstDayOfWeek) - CInt(jan1.DayOfWeek)
      Dim firstWeekDay As DateTime = jan1.AddDays(daysOffset)
      Dim curCulture As System.Globalization.CultureInfo = System.Globalization.CultureInfo.CurrentCulture
      Dim firstWeek As Integer = curCulture.Calendar.GetWeekOfYear(jan1, curCulture.DateTimeFormat.CalendarWeekRule, curCulture.DateTimeFormat.FirstDayOfWeek)
      If firstWeek <= 1 Then
          weekOfYear -= 1
      End If
      Return firstWeekDay.AddDays(weekOfYear * 7)
End Function

and here is the RegularExpressionValidator, although my format(07w42 means 42.week in year 2007) differs a little from yours.

<asp:RegularExpressionValidator ID="CalWeekFormat" runat="server" 
                                 ControlToValidate="TxtCalWeek" Display="None" EnableClientScript="true" 
                                 ErrorMessage="Enter valid Year/Calendarweek-Format: examplary format '09w23' or '9w23' for year 2009 and week 23" 
                                 style="visibility:hidden" 
                                 ValidationExpression="^\d{1,4}[wW](\d|[0-4]\d|5[0123])$" 
                                 ValidationGroup="VG_SAVE">*</asp:RegularExpressionValidator>