字典键存在时找不到它

本文关键字：找不到 存在 字典 | 更新日期: 2023-09-27 18:11:36

为什么我的字典说一个键不存在，当我刚刚插入它?是我的Equals方法还是双重比较?

代码如下:

// Test: I know the dictionary contains nCoord but its saying the key doesn't exist
Dictionary<UTMCoordinate, int> planes = new Dictionary<UTMCoordinate, int>();
UTMCoordinate nCoord    = new UTMCoordinate(337394.136407966, 6263820.40182064, 0, 56, UTMCoordinate.Hemisphere.H_SOUTHERN);
planes[nCoord]          = 1;
bool exists = planes.ContainsKey(nCoord);  // always returns false

我的UTMCoordinate实现如下:

public class UTMCoordinate
{
    public enum                 Hemisphere {H_NOTHERN, H_SOUTHERN};
    public const double         DIF_TOLERANCE    = 0.0005;
    public double               x               { get; set; }
    public double               y               { get; set; }
    public double               elev            { get; set; }
    public uint                 UTMZone         { get; set; }
    public Hemisphere           hemisphere      { get; set; }
    public UTMCoordinate(double x, double y, double elev=double.MinValue, uint utmZone=uint.MinValue, Hemisphere hemisphere=Hemisphere.H_SOUTHERN) {
        this.x          = x;
        this.y          = y;
        this.elev       = elev;
        this.UTMZone    = utmZone;
        this.hemisphere = hemisphere;
    }
    public override int GetHashCode() {
        unchecked // Overflow is fine, just wrap
        {
            int hash = 17;
            // Suitable nullity checks etc, of course :)
            hash = hash * 23 + x.GetHashCode();
            hash = hash * 23 + y.GetHashCode();
            hash = hash * 23 + elev.GetHashCode();
            hash = hash * 23 + UTMZone.GetHashCode();
            hash = hash * 23 + hemisphere.GetHashCode();
            return hash;
        }
    }
    public override bool Equals(object obj)
    {
        UTMCoordinate other = obj as UTMCoordinate;
        if (other == null)
            return false;
        return double.Equals(x, other.x) && double.Equals(y, other.y) && double.Equals(elev, other.elev) && uint.Equals(UTMZone, other.UTMZone) && double.Equals(hemisphere, other.hemisphere);
    }
}

编辑使用Daniel a . Whites的建议，我使用了不同的双重比较方法。不幸的是，它仍然没有识别密钥:

public override bool Equals(object obj)
{
    //return base.Equals (obj);
    UTMCoordinate other = obj as UTMCoordinate;
    if (other == null)
        return false;
    //return double.Equals(x, other.x) && double.Equals(y, other.y) && double.Equals(elev, other.elev) && uint.Equals(UTMZone, other.UTMZone) && double.Equals(hemisphere, other.hemisphere);
    return Math.Abs (x-other.x) <= DIF_TOLERANCE && Math.Abs (y-other.y) <= DIF_TOLERANCE && Math.Abs (elev-other.elev) <= DIF_TOLERANCE && uint.Equals(UTMZone, other.UTMZone) && hemisphere == other.hemisphere;
}

字典键存在时找不到它

如果我从你的问题中取出你的代码:

Dictionary<UTMCoordinate, int> planes = new Dictionary<UTMCoordinate, int>();
UTMCoordinate nCoord    = new UTMCoordinate(337394.136407966, 6263820.40182064, 0, 56, UTMCoordinate.Hemisphere.H_SOUTHERN);
planes[nCoord]          = 1;
bool exists = planes.ContainsKey(nCoord);

我得到的exists的值是true。

但是，如果我这样做:

nCoord.x = 1.0;
exists = planes.ContainsKey(nCoord);

exists的值突然变成了false，即使对象仍然在字典中。这是因为GetHashCode的值发生了变化。原来是-1473667404，但是在赋值了属性x之后，它变成了201352392。

字典使用GetHashCode的值来确定将键放在哪个桶中，因此当哈希码更改时，字典可能会尝试在错误的桶中找到键，然后报告它不包含键。

我怀疑你的代码就是这样。

所以你需要改变你的对象，使它是不可变的

public double               x               { get; private set; }
public double               y               { get; private set; }
public double               elev            { get; private set; }
public uint                 UTMZone         { get; private set; }
public Hemisphere           hemisphere      { get; private set; }
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