通用集合中的协方差

Question

I would like to do this

List<anotherclass> ls = new List<anotherclass> {new anotherclass{Name = "me"}};    
myGrid.ItemSource = ls;

at some other place

var d = myGrid.ItemSource as IEnumerable<Object>;    
var e = d as ICollection<dynamic>;
e.Add(new anotherclass());

I need to access the itemsource at different areas of the program. I need to add items to the List without compile time type information. Casting to IEnumerable works, but because I need to add items to the collection I need more than that, hence trying to cast it to a collection.

How can it be possible?

Answer 1

List<T> implements IList . So as long as you're sure you're adding the right type of object, you can use the Add method of this interface:

var d = (IList)myGrid.ItemSource;        
d.Add(new anotherclass());

Answer 2

The question is not: "Why does it work?", because, in fact, it doesn't work. It compiles but it will throw a NullReferenceException .
d as ICollection<dynamic> will return null because an List<anotherclass> isn't an ICollection<dynamic> but an ICollection<anotherclass> and ICollection<T> is not covariant.

The solution already has been provided by KooKiz .

Answer 3

Try this instead:

var d =(List<anotherclass>) myGrid.ItemSource;
d.Add(new anotherclass());

I think it is better to do a direct cast. If you use as it will throw a nullreferenceException when trying to add. It is better to have the invalidCastException that better describes what went wrong.