使用新对象作为键时字典找不到值

Question

在 Unity 3D 中，我正在尝试构建一个由 NodeCoordinates 键入的 PathNodes 字典。我已经在 NodeCoordinate 中覆盖了 GetHashCode，它应该返回一个恒定的唯一值。如果我遍历字典的键，查找工作正常，但如果我使用应该存在的 PathNode 的坐标创建一个新的 NodeCoordinate，即使哈希码相等，查找也会失败。

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class PathNode : MonoBehaviour {

    public static Dictionary<NodeCoordinate, PathNode> pathNodes;

    public PathNode left;
    public PathNode right;
    public PathNode forward;
    public PathNode backward;

    private NodeCoordinate coord;

    void Awake()
    {
        if (PathNode.pathNodes == null)
        {
            PathNode.pathNodes = new Dictionary<NodeCoordinate, PathNode>();
        }

        NodeCoordinate coord = new NodeCoordinate(transform.position.x, transform.position.z);
        this.coord = coord;
        PathNode.pathNodes.Add(coord, this);

        NodeCoordinate leftChord = new NodeCoordinate(coord.x - 1, coord.z);
        NodeCoordinate rightChord = new NodeCoordinate(coord.x + 1, coord.z);
        NodeCoordinate forwardChord = new NodeCoordinate(coord.x, coord.z + 1);
        NodeCoordinate backwardChord = new NodeCoordinate(coord.x, coord.z - 1);

        if (PathNode.pathNodes.ContainsKey(leftChord))
        {
            this.left = PathNode.pathNodes[leftChord];
            this.left.right = this;
        }
        if (PathNode.pathNodes.ContainsKey(rightChord))
        {
            this.right = PathNode.pathNodes[rightChord];
            this.right.left = this;
        }
        if (PathNode.pathNodes.ContainsKey(forwardChord))
        {
            this.forward = PathNode.pathNodes[forwardChord];
            this.forward.backward = this;
        }
        if (PathNode.pathNodes.ContainsKey(backwardChord))
        {
            this.backward = PathNode.pathNodes[backwardChord];
            this.backward.forward = this;
        }
    }

    private static bool debug = true;

    void Update()
    {
        if (debug)
        {
            foreach (NodeCoordinate coord in PathNode.pathNodes.Keys)
            {
                Debug.Log(coord + " : " + PathNode.pathNodes[coord] + " : " + coord.GetHashCode());
            }

            foreach (PathNode node in PathNode.pathNodes.Values)
            {
                NodeCoordinate leftChord = new NodeCoordinate(node.coord.x - 1, node.coord.z);
                PathNode leftNode;
                Debug.Log("Left: " + leftChord + " : " + PathNode.pathNodes.TryGetValue(leftChord, out leftNode) + " : " + leftChord.GetHashCode());
            }

            debug = false;
        }
    }
}

public class NodeCoordinate
{
    public float x;
    public float z;

    public NodeCoordinate(float x, float z)
    {
        this.x = x;
        this.z = z;
    }

    public bool Equals(NodeCoordinate coord)
    {
        return (this.x == coord.x && this.z == coord.z);
    }

    public override int GetHashCode()
    {
        return string.Format("{0}x{1}", this.x, this.z).GetHashCode();
    }

    public override string ToString()
    {
        return "Coordinate: " + this.x + " x " + this.z;
    }
}

这是我的小调试的输出： debug log

如您所见，在遍历键时，哈希码为 2137067561 和 1824497336 的查找有效，但是当我实例化一个新的 NodeCoordinate 并尝试查找它时，它具有相同的哈希码但查找失败。知道为什么会这样吗？谢谢。

Answer 1

问题在于您的NodeCoordinate 类没有以字典使用的方式定义相等性。你有这样的方法：

public bool Equals(NodeCoordinate coord)

...但您既不覆盖IEquatable<NodeCoordinate>，也不覆盖Equals(object)。

我个人建议两者都做 - 并实现一个不需要字符串格式化的更简单的哈希码：

public sealed class NodeCoordinate : IEquatable<NodeCoordinate>
{
    public float X { get; }
    public float Z { get; }

    public NodeCoordinate(float x, float z)
    {
        X = x;
        Z = z;
    }

    public override Equals(object other) => Equals(other as NodeCoordinate);

    public bool Equals(NodeCoordinate coord) =>
        coord != null && this.X == coord.X && this.Z == coord.Z;

    public override int GetHashCode()
    {
        int hash = 23;
        hash = hash * 31 + X;
        hash = hash * 31 + Z;
        return hash;
    }

    public override string ToString() => $"Coodinate: {X} x {Z}";
}

（请注意，我也将其设为不可变并使用属性而不是公共字段。为简单起见，我使用了 C# 6 语法，但如果需要，将其转换为 C# 5 并不难。）

Answer 2

因此，由于某种原因，当我添加具有完全相同逻辑的 IEqualityComparer 时，它可以工作。

将字典的声明改为：

if (PathNode.pathNodes == null)
        {
            PathNode.pathNodes = new Dictionary<NodeCoordinate, PathNode>(new NodeCoordinateComparer());
        }

添加了这个：

public class NodeCoordinateComparer : IEqualityComparer<NodeCoordinate>
{
    public bool Equals(NodeCoordinate a, NodeCoordinate b)
    {
        return (a.x == b.x && a.z == b.z);
    }

    public int GetHashCode(NodeCoordinate coord)
    {
        return string.Format("{0}x{1}", coord.x, coord.z).GetHashCode();
    }


}