Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

Custom Class used as key in Dictionary but key not found

I have a class, show below, which is used as a key in a Dictionary<ValuesAandB, string> I'm having issues when trying to find any key within this dictionary, it never finds it at all. As you can see, I have overridden Equals and GetHashCode.

To look for the key I'm using

ValuesAandB key = new ValuesAandB(A,B);
if (DictionaryName.ContainsKey(key)) {
   ...
}

Is there anything else that I'm missing? Can anyone point out what I'm doing wrong?

private class ValuesAandB {
   public string valueA;
   public string valueB;

   // Constructor
   public ValuesAandB (string valueAIn, string valueBIn) {
     valueA = valueAIn;
     valueB = ValueBIn;
   }

   public class EqualityComparer : IEqualityComparer<ValuesAandB> {
      public bool Equals(ValuesAandB x, ValuesAandB y) {
         return ((x.valueA.Equals(y.valueA)) && (x.valueB.Equals(y.valueB)));
      }
      public int GetHashCode(ValuesAandB x) {
         return x.valueA.GetHashCode() ^ x.valueB.GetHashCode();
      }
   }
}

And before anyone asks, yes the values are in the Dictionary!

like image 376
Ian Devlin Avatar asked Oct 27 '09 18:10

Ian Devlin


3 Answers

How are you constructing the dictionary? Are you passing your custom equality comparer in to its constructor?

like image 185
2 revs, 2 users 57% Avatar answered Sep 30 '22 14:09

2 revs, 2 users 57%


You have not overridden Equals and GetHashCode. You have implemented a second class which can serve as an EqualityComparer. If you don't construct the Dictionary with the EqualityComparer, it will not be used.

The simplest fix would be to override GetHashCode and Equals directly rather than implementing a comparer (comparers are generally only interesting when you need to supply multiple different comparison types (case sensitive and case insensitive for example) or when you need to be able to perform comparisons on a class which you don't control.

like image 35
StarPacker Avatar answered Oct 23 '22 16:10

StarPacker


I had this problem, turns out the dictionary was comparing referances for my key, not the values in the object.

I was using a custom Point class as keys. I overrode the ToString() and the GetHashCode() methods and viola, key lookup worked fine.

like image 1
Muad'Dib Avatar answered Oct 23 '22 15:10

Muad'Dib