Problem with generics collections

demitry · November 21st, 2005, 11:26 AM

Problem with Generic.Dictionary and Generic.SortedDictionary.
ContainsValue function of both of these classes work with usuall datatypes. But when you make a collection of the objects of a class that you have defined yourself it doesnt work.

I know that it requires you to implement IComparable which i have done. And this implementation works fine for the other function - Sort- that demands.

Please help.

Apologies for posting this query more than once. But i'm just making sure that it gets attention of people in all the relevant forums.

Jeff Mason · November 21st, 2005, 01:41 PM

I think you have to implement the IEquatable interface to define the Equals method for the class in question. IComparable is for ordering instances of a class (e.g. for sorting), but I'm pretty sure ContainsValue doesn't use IComparable, but instead IEquatable.

Jeff Mason
Custom Apps, Inc.
www.custom-apps.com

demitry · November 21st, 2005, 05:28 PM

Perfact. Jeff, u saved some of my hair from being uprooted. This forum lived up to its reputation. It's my first expereriance and it has been a life saver. Thanks.
But now I'm wondering why is the documentation misleading people. It hardly said anything about this interface.

Demitry

Jeff Mason · November 22nd, 2005, 01:56 PM

Well, not that I am trying to defend the documentation (since IMO it has many problems) but if you look at the docs for the Dictionary.ContainsValue method, you'll see:

Quote:

quote:
This method determines equality using the default equality comparer EqualityComparer.Default for TValue, the type of values in the dictionary.

and if you then follow the entry for EqualityComparer.Default you'll see

Quote:

quote:
The Default property checks whether type T implements the System.IEquatable generic interface and if so returns an EqualityComparer that uses that implementation. Otherwise it returns an EqualityComparer that uses the overrides of Object.Equals and Object.GetHashCode provided by T.

I say it's hard to get much clearer than that.

I guess you just need to know where to look. ;)

Jeff Mason
Custom Apps, Inc.
www.custom-apps.com

demitry · November 24th, 2005, 06:39 AM

U are right Jeff, probably i should have checked the online docs as well. In the documentation that ships with the .NET 2.0 beta theye didnt say anything about this interface. So- lesson learned- and from now on I'm gonna rely only on the online version of the documentation. Thanks for time.