Question

I have ControlA which accepts an IInterfaceB which has a property of type List<unknownType>

In an event of ControlA i need to add a new instance of unknownType to the List in IInterfaceB…

unknownType needs specific properties so i immediately thought it could be an interface, but quickly realised interfaces cannot be instantiated…

How would you design this system?

EDIT the current inheritance chain looks like this:

topLevelClass -> baseObject -> IBaseObject (which is implemented in topLevelClass) 

so if i added a new class to the chain it would need to do the inheriting and implementing which would be impossible (afaik)

Answer 1

If I’m interpreting this correctly, you could add a constraint on unknownType to be of some interface that contains the properties you need:

class ControlA {     void Frob<T>(IInterfaceB<T> something) where T : IHasSomeProperties, new()     {         something.ListOfT.Add(new T() { SomeProperty = 5 });         something.ListOfT.Add(new T() { SomeProperty = 14 });     } }