C# List<T> Contains test

Question

Is this kind of if-testing necessary when removing an item?

if (_items.Contains(item))
{
    _items.Remove(item);
}

And, what about this test?

if (!_items.Contains(item))
{
    _items.Add(item);
}

Answer 1

You don't have to test to remove. Remove() will return false if it didn't remove anything.

If you don't want duplicate items in your list you can test, before adding. Otherwise, you'll have duplicates.

See also: http://msdn.microsoft.com/en-us/library/6sh2ey19.aspx

Answer 2

You could also use a HashSet<T> if you want to be able to Add() an item multiple times and have it only exist in the collection once, without checking Contains() first.