c# - 包装 List.Add() 给出 - 未将对象引用设置为对象的实例

Question

我想用我的自定义类包装 List 类。至于现在我有这样的东西;

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_);
    }
}

当我现在做

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

我也尝试过不使用 ref 但结果相同。我在这里做错了什么？

Answer 1

您实际上从未实例化 List<Node> .

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