我只想在每个月的最后一天发射代码，就是这么简单……

if (DateTime.UtcNow.AddDays(1).Day != 1)
{
    // Tomorrow is not the first...
    return;
}

你可以通过下面的代码找到任何月份的最后一天:

var now = DateTime.Now;
var startOfMonth = new DateTime(now.Year, now.Month, 1);
var DaysInMonth = DateTime.DaysInMonth(now.Year, now.Month);
var lastDay = new DateTime(now.Year, now.Month, DaysInMonth);

您可以按以下方式扩展DateTime;

public static class DateTimeMethods
{
    public static DateTime StartOfMonth(this DateTime date)
    {
        return new DateTime(date.Year, date.Month, 1, 0, 0, 0);
    }

    public static DateTime EndOfMonth(this DateTime date)
    {
        return date.StartOfMonth().AddMonths(1).AddSeconds(-1);
    }
}

像这样使用它;

DateTime today = DateTime.Now;

DateTime startOfMonth = today.StartOfMonth();
DateTime endOfMonth = today.EndOfMonth();

var lastDayOfMonth = DateTime.DaysInMonth(date.Year, date.Month);

例如2021年5月7日

DateTime.Now.Day;

结果:5

DateTime.Now.AddMonths（+1）.AddDays（-DateTime.Now.Day）.ToString（“yyyy-MM-dd”）;

结果:2021/07/31

这将显示下个月的最后日期。可以从AddMonths(x)中添加或减去想要返回的月份。

DateTime.Now.AddMonths(2).AddDays(-DateTime.Now.Day)