使用VB.NET查找星期一的日期

Question

我需要找到一種方法來查找我們所在星期一的星期一的日期（DD/MM/YYYY）。

例如，本週，星期一將是09/11/2009，如果這是下週，它將是16/11/2009。

我設法得到代碼形式的地方，但我得到的是'不能轉換爲整數'的錯誤。我使用Date.Today和AddDays（）。

感謝您的任何幫助。 :)

Answer 1

DateTime.DayOfWeek是一個枚舉，指示給定日期的某一天。

Dim monday As DateTime = Today.AddDays((Today.DayOfWeek - DayOfWeek.Monday) * -1) 

Answer 2

=Format(DateAdd("d", (-1 * WeekDay(Date.Today()) + 2), Date.Today()), "dd/MM/yyyy") 

Answer 3

如果週日是一週的第一天，你可以簡單地這樣做：

Dim today As Date = Date.Today 
Dim dayDiff As Integer = today.DayOfWeek - DayOfWeek.Monday 
Dim monday As Date = today.AddDays(-dayDiff) 

由於週一是1，你可以用下面的代碼中找到當前周的星期一

如果星期一是一週的第一天：

Dim today As Date = Date.Today 
Dim dayIndex As Integer = today.DayOfWeek 
If dayIndex < DayOfWeek.Monday Then 
    dayIndex += 7 'Monday is first day of week, no day of week should have a smaller index 
End If 
Dim dayDiff As Integer = dayIndex - DayOfWeek.Monday 
Dim monday As Date = today.AddDays(-dayDiff) 

Answer 4

一個簡單的方法應該得到你想要的東西：

private static DateTime GetMondayForWeek(DateTime inputDate) 
    { 
     int daysFromMonday = inputDate.DayOfWeek - DayOfWeek.Monday; 
     return inputDate.AddDays(-daysFromMonday); 
    } 

您還可以擴展它，你想和任何一天：

private static DateTime GetDayForWeek(DateTime inputDate, DayOfWeek inputDay) 
    { 
     int daysAway = inputDate.DayOfWeek - inputDay; 
     return inputDate.AddDays(-daysAway); 
    } 

調用第一個例子，是使用類似：

DateTime mondayDate = GetMondayForWeek(new DateTime(2009, 11, 15)); 
Console.WriteLine(mondayDate); 

Answer 5

有一週中的一天可以使用的方法

Dim instance As DateTime 
Dim value As DayOfWeek 

value = instance.DayOfWeek 

請參閱：http://msdn.microsoft.com/en-us/library/system.datetime.dayofweek.aspx

Answer 6

我只是在我正在進行的一個項目中做到這一點 - 我保證，這是正確的。這是返回給定日期後第n個星期一的方法。如果給定的日期是星期一，它將返回下一個星期一。

Public Function GetSubsequentMonday(ByVal startDate As DateTime, ByVal subsequentWeeks As Integer) As DateTime 
    Dim dayOfWeek As Integer = CInt(startDate.DayOfWeek) 
    Dim daysUntilMonday As Integer = (Math.Sign(dayOfWeek) * (7 - dayOfWeek)) + 1 
    'number of days until the next Monday 
    Return startDate.AddDays(CDbl((daysUntilMonday + (7 * (subsequentWeeks - 1))))) 
End Function 

Answer 7

從我的意見元騎士的回答繼，這裏是一個簡短的功能，使我在評論中提到的修正：

Public Function GetFirstOfLastWeek() As DateTime 
Dim today As DateTime, daysSinceMonday As Integer 
    today = DateTime.Today 
    daysSinceMonday = today.DayOfWeek - DayOfWeek.Monday 
    If daysSinceMonday < 0 Then 
     daysSinceMonday += 7 
    End If 
    Return today.AddDays(-daysSinceMonday) 
End Function 

Answer 8

如果你每週從週一開始，那麼你可以使用這樣的事情：

DateTime mondayDate = DateTime.Now.AddDays(((DateTime.Now.DayOfWeek == DayOfWeek.Sunday?7: (int)DateTime.Now.DayOfWeek) - 1)*-1); 

DateTime sundayDate = DateTime.Now.AddDays(7 - (DateTime.Now.DayOfWeek == DayOfWeek.Sunday?7: (int)DateTime.Now.DayOfWeek)); 

Answer 9

另一種方法，如果週一是第一天，是這樣的：

Dim today As Date = Date.Today 
       Dim dayDiff As Integer = today.DayOfWeek - DayOfWeek.Monday 
       Dim monday As Date = today.AddDays(-dayDiff) 

       dayDiff = DayOfWeek.Saturday - today.DayOfWeek + 1 
       Dim sunday As Date = today.AddDays(dayDiff)