日历无法在第一周显示前几个月的天数

Question

I'm learning C# and I wanted to make a calendar to learn DateTime. I did make a calendar but now I want to see previous months days in first week like in this photo . I tried few things but I really don't remember all. Here is my code and if there any way to improve it just say. I'm using WinForms for ui.

            DateTime now = DateTime.Now;

            Month = now.Month;
            Year = now.Year;

            // count of days of the month
            int days = DateTime.DaysInMonth(Year, Month);
            // first day of the month
            DateTime startofthemonth = new DateTime(Year, Month,1);
            // last day of the month
            var endofthemonth = startofthemonth.AddDays(-1);
            // convert the startofthemonth to int
            int dayoftheweek = Convert.ToInt32(startofthemonth.DayOfWeek.ToString("d")) + 6;
            // convert the endofthemonth to int
            int lastdayinmonth = Convert.ToInt32(endofthemonth.DayOfWeek.ToString("d"));
            // blank user control
            for (int i = lastdayinmonth; i <= lastdayinmonth; i--)
            {
                UCBlankDay uCBlankDay = new UCBlankDay();
                uCBlankDay.BlankDays(i);
                flowLayoutPanel1.Controls.Add(uCBlankDay);
            }
            // day user control
            for (int i = 1; i <= days; i++)
            {
                UCDay uCDay = new UCDay();
                uCDay.Days(i);
                flowLayoutPanel1.Controls.Add(uCDay);
            }
        }

to be clear code works without showing previous months days in first week

Answer 1

I've recently done a calendar and I found that when you are in the month view, it's better to divide your month in weeks first instead of days right away.

I would use your 1st day of the month and find the first day of the week doing something like this:

    public static DateTime StartOfWeek(this DateTime dt, DayOfWeek startOfWeek)
    {
        int diff = (7 + (dt.DayOfWeek - startOfWeek)) % 7;
        return dt.AddDays(-1 * diff).Date;
    }

    startofthemonth = date.StartOfMonth().StartOfWeek(startDay);

I would then iterate by weeks instead of days like this

        do
        {
            Weeks.Add(new UCBlankWeek(**Your day logic will be inside this constructor**));

            startofthemonth = startofthemonth.AddDays(7);
            currentMonth = startofthemonth.Month;
        }
        while (currentMonth == MonthNumber);

You can loop 7 times inside the constructor of everyweek and put you logic in there.

Hope this helps with your issue!