How can I get the DateTime for the start of the week?

Question

How do I find the start of the week (both Sunday and Monday) knowing just the current time in C#?

Something like:

DateTime.Now.StartWeek(Monday);
         


        

Answer 1

Ugly but it at least gives the right dates back

With start of week set by system:

    public static DateTime FirstDateInWeek(this DateTime dt)
    {
        while (dt.DayOfWeek != System.Threading.Thread.CurrentThread.CurrentCulture.DateTimeFormat.FirstDayOfWeek)
            dt = dt.AddDays(-1);
        return dt;
    }

Without:

    public static DateTime FirstDateInWeek(this DateTime dt, DayOfWeek weekStartDay)
    {
        while (dt.DayOfWeek != weekStartDay)
            dt = dt.AddDays(-1);
        return dt;
    }