Question

I’m writing a program in C# that has a custom collection. The custom collection performs some useful aggregate functions (AllSuccessful, %Successful, etc) over it’s members which are of type ResultInfo. I have several classes that derive from ResultInfo (UploadResultInfo, XUploadResultInfo, and YUploadResultInfo), and would like to have additional collections that inherit from ResultInfoCollection that have additional aggregate functions. The only problem with doing this as specified is that it leaves a useless

public void Add(ResultInfo item) {   } 

on the collection. Clarification: This method takes an argument of type ResultInfo, but a ResultInfo added to an UploadResultInfoCollection will throw an error. Is there an elegant way of solving my problem? I’ve considered generics but I don’t quite know how that would work.

Answer 1

To define a generic class that handles any child of ResultInfo you just define it like

public class MyCollection<T> : ICollection<T> where T : ResultInfo {       ... the required methods ... just use 'T' instead of 'ResultInfo' ...      public void Add(T item) {} } 

Later on you can use it by

 MyCollection<FooResultInfo> coll = new MyCollection<FooResultInfo>(); 

Just try using them, they are not too difficult and learning by doing is the best way …