Question

I have a generic class containing a special collection. An instance of this collection is passed to a method as object. Now I have to call one of the generic class’ methods. The problem I see is that I don’t know which type the items in the collection are of so that I can’t cast before using the property.

public class MyGenericCollection<T>: ReadOnlyObservableCollection<T>
{
  public bool MyProperty
  {
    get
    {
      // do some stuff and return
    }
  }
}

public bool ProblematicMethod(object argument)
{
  MyGenericCollection impossibleCast = (MyGenericCollection) argument;
  return impossibleCast.MyProperty;
}

Is there a way around this problem?

Answer 1

In this case, it may be worth adding an interface containing all your non-generic members:

public IHasMyProperty
{
    bool MyProperty { get; }
}

then make the collection implement it:

public class MyGenericCollection<T>: ReadOnlyObservableCollection<T>,
    IHasMyProperty

then take an IHasMyProperty in your method:

public bool ProblematicMethod(IHasMyProperty argument)
{
    return argument.MyProperty;
}

or keep taking object, but cast to the interface:

public bool ProblematicMethod(object argument)
{
    return ((IHasMyProperty)argument).MyProperty;
}

In other cases you could have a non-generic abstract base class which your generic class extends, but in this case you’re already deriving from a generic class (ReadOnlyObservableCollection<T>) which removes that option.