Why does List<T> blow up when i index into it?

I created a list as a class level field like this:

private readonly IList<int> _intCol = new List<int>();

I then index into it and it blows up with the exception below:

_intCol[0] = 0;

Exception:

Index was out of range. Must be non-negative and less than the size of the开发者_StackOverflow collection.Parameter name: index

At this point, _intCol is a list of the size 0, it does not have an element on the first position.

You can use _intCol.Add(0);.

See also:

• List<T>.Add(T)
• List<T>.Insert(int, T)

If you do want to insert elements that way, you can use a Dictionary<int,int>, but note that your elements are not ordered - you just map numbers to numbers. For example:

Dictionary<int, int> integers = new Dictionary<int, int>();
integers[0] = 13;
integers[42] = 14;

integers now has two items, in no particular order:

{42: 14, 0: 13}

If you haven't populated the list with any elements, then trying to reference element 0 will fail just like that. You should check the Count first, and not reference any element index greater than Count-1.