给定的DateTime键在词典中不存在

Question

I am a very beginner of C# and programming. I am trying to calculate a few DateTime variables. The first one is called dDate and second dDate1 (the previous day of dDate ), third dDate2 (the second previous day of dDate , ie, the previous day of dDate1 ), the fourth dDate3 (the third previous day of dDate , ie, the second previous day of dDate1 and the previous day of dDate2 ). They must be not holidays or weekends!

I've had all holidays and weekends stored in a dictionary called nd<DateTime, string> . The key DateTime has a series of date from 2011-01-01 to 2013-01-01 , step by one day and the value string is either TR or NT , a string variable but not boolean. If it is weekend or holiday, string is NT , otherwise TR .

What I am trying to do is when dDate is weekend or holiday, minus one day. For example, dDate is 2012-01-02 which is a holiday, change dDate to 2012-01-01 , and because it is weekend (Sunday), change it to 2011-12-31 , and it is weekend again, change dDate to 2011-12-30 . Same to dDate1 , dDate2 and dDate3 .

The problem here is my code works fine for dDate . But it gives an error:

the given key was not present in the dictionary

when I am doing the same thing for dDate1 , dDate2 or dDate3 . The code is attached below:

 private Dictionary<DateTime, string> noDates;
 ...
 noDates = new Dictionary<DateTime, string>();

 public void ImportNoDate()
 {
      string str;
      string[] line = new string[0];
      while ((str = reader.ReadLine()) != null) 
      {
         line = str.Split(',');
         String date = line[1];
         String flag = line[2];//flag is "NT" or "TR"
         String[] tmp = date.Split('-');
         date = Convert.ToInt32(tmp[0]) + "-" + Convert.ToInt32(tmp[1]) + "-" + Convert.ToInt32(tmp[2]);

         DateTime noDate = DateTime.Parse(date);
         noDates.Add(noDate, flag);
     }
  }

public void ImportdDate()
{
    ...
    DDates dd = new DDates(dDate, noDates); //dDate is defined similar to noDate, it is just another //series of date
}

    //DDates is an auxiliary cs file called DDates.cs
    public DDates(DateTime dd, Dictionary<DateTime, string> nd)
    {
         dDate1 = dDate.AddDays(-1);
         dDate1 = dDate.AddDays(-2);
         dDate3 = dDate.AddDays(-3);

       // dDate is imported from data file and has been Parse
      // to DateTime and it is something like
      // 2012-01-01 12:00:00 AM

     if (nd.ContainsKey(dDate))
     {
        while (nd[dDate].Contains("NT"))
       {
          dDate = dDate.AddDays(-1);
       }
    }

   //It works fine till here:
   if (nd.ContainsKey(dDate1))
   {
      //It gives "the given key was not present in the dictionary" here:
      while (nd[dDate1].Contains("NT"))
      {
        dDate1 = dDate1.AddDays(-1);
      }
   }
}

Answer 1

From your description it looks like what you are trying to do is for a given date find the first non holiday date.

Using a dictionary and storing every possible date is not the correct solution for this.

Personally I think a HashSet<DateTime> plus a little math would be the best solution. In fact I was bored so I wrote it up

static class HolidayTester
{
    private static HashSet<DateTime> fixedHolidays = new HashSet<DateTime>(new DayOnlyComparer())
        {
            new DateTime(1900,1,1), //New Years
            new DateTime(1900,7,4), //4th of july
            new DateTime(1900,12, 25) //Christmas
        };


    /// <summary>
    /// Finds the most recent workday from a given date.
    /// </summary>
    /// <param name="date">The date to test.</param>
    /// <returns>The most recent workday.</returns>
    public static DateTime GetLastWorkday(DateTime date)
    {
        //Test for a non working day
        if (IsDayOff(date))
        {
            //We hit a non working day, recursively call this function again on yesterday.
            return GetLastWorkday(date.AddDays(-1));
        }

        //Not a holiday or a weekend, return the current date.
        return date;
    }


    /// <summary>
    /// Returns if the date is work day or not.
    /// </summary>
    /// <param name="testDate">Date to test</param>
    /// <returns>True if the date is a holiday or weekend</returns>
    public static bool IsDayOff(DateTime testDate)
    {
      return date.DayOfWeek == DayOfWeek.Saturday ||
             date.DayOfWeek == DayOfWeek.Sunday || //Test for weekend
             IsMovingHolidy(testDate) || //Test for a moving holiday
             fixedHolidays.Contains(testDate); //Test for a fixed holiday
    }


    /// <summary>
    /// Tests for each of the "dynamic" holidays that do not fall on the same date every year.
    /// </summary>
    private static bool IsMovingHolidy(DateTime testDate)
    {
        //Memoral day is the last Monday in May
        if (testDate.Month == 5 && //The month is May 
                testDate.DayOfWeek == DayOfWeek.Monday && //It is a Monday
                testDate.Day > (31 - 7)) //It lands within the last week of the month.
            return true;

        //Labor day is the first Monday in September
        if (testDate.Month == 9 && //The month is september
                testDate.DayOfWeek == DayOfWeek.Monday &&
                testDate.Day <= 7) //It lands within the first week of the month
            return true;


        //Thanksgiving is the 4th Thursday in November
        if (testDate.Month == 11 && //The month of November
            testDate.DayOfWeek == DayOfWeek.Thursday &&
            testDate.Day > (7*3) && testDate.Day <= (7*4)) //Only durning the 4th week
            return true;

        return false;
    }


    /// <summary>
    /// This comparer only tests the day and month of a date time for equality
    /// </summary>
    private class DayOnlyComparer : IEqualityComparer<DateTime>
    {
        public bool Equals(DateTime x, DateTime y)
        {
            return x.Day == y.Day && x.Month == y.Month;
        }

        public int GetHashCode(DateTime obj)
        {
            return obj.Month + (obj.Day * 12);
        }
    }
}

Now it does not follow your rules exactly, this code tests if a day is a work day and keeps walking backwards till it hits the first non work day. It would be easy enough to modify, however I did not want to solve your problem exactly so you could learn a little (Unless I misunderstood the algorithm and I did solve the problem, in that case... your welcome)

The way you would use it is simply put in a date and then use that to decide if you are going to return TR or NT

public static string GetDateLabel(DateTime testDate)
{
    if(HolidayTester.IsDayOff(testDate))
        return "NT";
    else
        return "TR";
}

If you want to know the last working day you can call that directly from HolidayTester.GetLastWorkday(DateTime)