Using generics in abstract classes

Question

I'm working on an abstract class where the implementing class needs to implement a list of T. The problem is that this doesn't work:

public class AbstractClass {     public int Id { get; set; }     public int Name { get; set; }      public abstract List<T> Items { get; set; } }  public class Container : AbstractClass {     public List<Widgets> Items { get; set; } } 

I'm sure that there is an obvious answer that I'm missing, and I know that I can build an abstract base type to put in the list, but when I use my Linq command to build the list, the abstract type (ItemBase) doesn't play nicely with the .ToList() method. Is what I'm trying to do so unique?

Answer 1

You need the declaration on the class as well, to know what type T is:

public abstract class AbstractClass<T> {     public int Id { get; set; }     public int Name { get; set; }      public abstract List<T> Items { get; set; } }  public class Container : AbstractClass<Widgets> {     public override List<Widgets> Items { get; set; } } 

You can also restrict what T can be, like say it must implement IWidgets:

public class AbstractClass<T> where T : IWidgets