Getting a NullReferenceException when trying to compare to null

Question

first time posting on here and a bit of a noob in c#. Basically I'm creating a linkedlist and initializing it to null at the beginning of my class. When I'm ready to use it, I check to make sure that it's not equal to the string passed by the method. I immediately get a NullReferenceException, and i'm supposed to be comparing it to null. Any fixes?

private DoubleLinkedListCell<DoubleLinkedListCell<GamePiece>> _columns = null;

public void FindColumn(string columnId)
    {

        bool right = true;
        while (_columns.Id != columnId)
        {
            if (_columns.Next == null)
            {
                right = false;
            }
            if (right)
            {
                Columns = Columns.Next;
            }
            else
            {
                Columns = Columns.Prev;
            }
        }

    }

Check the line you get the exception on. It's probably not where you think it's happening... — lc., Sep 29 '17 at 04:00
`_columns` is null. You are not initializing it before using it looks like — Chetan Ranpariya, Sep 29 '17 at 04:03

score 0 · Answer 1 · answered Sep 29 '17 at 04:06

0

You will get null reference if u try to access any property or member of _columns List (ex _columns.Id,_columns.Next etc..) so initialize it in constructor or direct when u declare field

answered Sep 29 '17 at 04:06

G.L

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Getting a NullReferenceException when trying to compare to null

1 Answers1