Sort month and year in listbox C#

string[] names = listBox1.Items.Cast<string>().ToArray();

int month = DateTime.ParseExact(MonthNameStr, "MMMM", CultureInfo.CurrentCulture).Month;

It is not as difficult as it seems if you are familiar with LINQ.

//read the lines into an array
var lines = File.ReadAllLines(@"C:\temp\TestDates.txt");
List<DateTime> dates = new List<DateTime>();
//parse the dates and add then to a list
foreach (var line in lines)
{
    string format = "yyyy - MMMM";
    var date = DateTime.ParseExact(line, format, CultureInfo.InvariantCulture);
    dates.Add(date);
}
//from the dates select a value tuple of type (DateTime date,int index)
var index = dates.Select((d, i) => (d, i))
                 //Sort by DateTime
                 .OrderBy(t => t.d)
                 //Select the index value
                 .Select(t => t.i);
//use the index value to index into the original lines
foreach (var i in index)
{
    //write out the lines in sorted order
    Console.WriteLine(lines[i]);
}

Console.ReadLine();