Error: Cannot implicitly convert type 'void' to 'System.Collections.Generic.List'

Question

I am trying to set a property of my .ascx controls from an .aspx using that control.

So in one of my .aspx which has this control in it, I have the

Answer 1

new List<Item>().Add(item);

This line returns void.

Try:

var list = new List<Item>();
list.Add(item);
ItemListt.ItemList = list;

Answer 2

You can't do that because the Add function returns void, not a reference to the list. You can do this:

mycontrol.ItemList = new List<Item>();
mycontrol.ItemList.Add(item);

or use a collection initializer:

mycontrol.ItemList = new List<Item> { item };

Answer 3

So long as ItemList is instantiated on your usercontrol, you can just do UserControl.ItemList.Add(item)

Answer 4

The Add method doesn't return a reference to the list. You have to do this in two steps:

ItemListt.ItemList = new List<Item>();
ItemListt.ItemList.Add(item);

Alternatively use a local variable to hold the reference before you put it in the property:

List<Item> list = new List<Item>();
list.Add(item);
ItemListt.ItemList = list;

Answer 5

ItemListt.ItemList = new List<Item>().Add(item);

Does Add method return an instance of a list based class?

EDIT: No, see this link for documentation on List<T>.Add

EDIT2: Try writing this piece of code & see what is the return value of Add method.

List<Item> items = new List<Item>();
var modifiedList = items.Add(myItem);

You will see that, the code should fail at Add because it returns void.

Answer 6

After creating the List<Item> you're immediately calling Add on it, which is a method returning void. This cannot be converted to the type of ItemList.ItemList.

You should do this instead:

var list = new List<Item>();
list.Add(item);
ItemList.ItemList = list;