using System;

using System.Globalization;

using System.Linq;

// see: https://stackoverflow.com/q/5366285/1016343

public class Program

{

    public static void Main()

    {

        var dtStr = "2011-03-21 13:26";

​

        var dt1 = dtStr.ToDate("yyyy-MM-dd HH:mm");

        Console.WriteLine(dt1.HasValue ? $"Parsed date: {dt1.Value.ToString()}" : "no valid date");

​

        var dt2 = dtStr.ToDate(new string[] { "yyyy-MM-dd HH:mm", "M/d/yyyy h:mm:ss tt" });

        Console.WriteLine(dt2.HasValue ? $"Parsed date: {dt2.Value.ToString()}" : "no valid date");

​

        int? year = dtStr?.ToDate("yyyy-MM-dd HH:mm")?.Year;

        Console.WriteLine(year.HasValue ? $"The year is: {year.Value.ToString()}" : "no valid year");

        var patterns=new[] { "dd-MM-yyyy", "dd.MM.yyyy" };

        (new[] { "15-01-2019", "15.01.2019" }).Select(s => s.ToDate(patterns)).Dump(); 

        (new[] { "15-01-2019", "15.01.2019" }).Select(s => s.ToDate("dd-MM-yyyy", "dd.MM.yyyy")).Dump(); 

    }

}

​

// using System.Globalization;

public static class Extensions

{

    public static DateTime? ToDate(this string dateTimeStr, params string[] dateFmt)

    {

        // example: var dt = "2011-03-21 13:26".ToDate(new string[]{"yyyy-MM-dd HH:mm", 

        //                                                  "M/d/yyyy h:mm:ss tt"});

        const DateTimeStyles style = DateTimeStyles.AllowWhiteSpaces;

        if (dateFmt == null)

        {

            var dateInfo = System.Threading.Thread.CurrentThread.CurrentCulture.DateTimeFormat;

            dateFmt=dateInfo.GetAllDateTimePatterns();

        }

        var result = (DateTime.TryParseExact(dateTimeStr, dateFmt,

            CultureInfo.InvariantCulture, style, out var dt)) ? dt : null as DateTime?;

        return result;

    }

}