c# – Wrapping List.Add()给出 – 对象引用未设置为对象的实例

我想用自定义类包装List类.至于现在我有这样的事情;

public class PrioritylistofNodes
{

    private List<Node>          list_;
    private IComparer<Node>     sorter_;

    public List<Node> List_ {
            get {return list_;}
            set {list_ = value;}
    }

    public PrioritylistofNodes ()
    {
            sorter_ = new NodeSorter_fValueDescending ();
    }

    public Node PopFromEnd ()
    {
            Node temp = new Node (list_ [list_.Count - 1]);
            list_.RemoveAt (list_.Count - 1);
            return temp;
    }

    public Node PeekFromEnd ()
    {
            return list_ [list_.Count - 1];
    }

    public void Add (ref Node toAdd)
    {
            Debug.Log (toAdd);
            list_.Add (toAdd);
            list_.sort (sorter_);
    }
}

我什么时候做

Node temp = new Node(10,20); //custom constructor
PrioritylistofNodes l = new PrioritylistofNodes();
l.add(temp);

我得到运行时异常：

Object reference not set to an instance of an object

我也试过没有参考,但结果相同.我在这做错了什么？

解决方法

您永远不会实际实例化List< Node>.

public PrioritylistofNodes ()
    {
            sorter_ = new NodeSorter_fValueDescending ();
            list_ = new List<Node>();
    }