为什么不Hashtable的回报如此"&的containsKey QUOT;类型为byte []在C＃中的关键？ [英] Why won't a Hashtable return true for "ContainsKey" for a key of type byte[] in C#?

问题描述

考虑下面的代码：

byte[] bytes = new byte[] { 1, 2, 5, 0, 6 };
byte[] another = new byte[] { 1, 2, 5, 0, 6 };

Hashtable ht = new Hashtable();
ht.Add(bytes, "hi");
Assert.IsTrue(ht.ContainsKey(another));

为什么这个断言失败？作为一个基本类型的数组不应该使用对象引用中使用，它应该？因此，它为什么会返回false？有什么我可以做，使此哈希表的工作。

Why does this assertion fail? Being an array of a primitive type shouldn't use using the object reference, should it? So why would it return false? Is there anything I can do to make this hashtable work?

推荐答案

下面是一个示例实现：

  class Program {
    static void Main(string[] args) {
      byte[] bytes = new byte[] { 1, 2, 5, 0, 6 };
      byte[] another = new byte[] { 1, 2, 5, 0, 6 };

      Hashtable ht = new Hashtable(new ByteArrayComparer());
      ht.Add(bytes, "hi");
      System.Diagnostics.Debug.Assert(ht.ContainsKey(another));
    }

    private class ByteArrayComparer : IEqualityComparer {
      public int GetHashCode(object obj) {
        byte[] arr = obj as byte[];
        int hash = 0;
        foreach (byte b in arr) hash ^= b;
        return hash;
      }
      public new bool Equals(object x, object y) {
        byte[] arr1 = x as byte[];
        byte[] arr2 = y as byte[];
        if (arr1.Length != arr2.Length) return false;
        for (int ix = 0; ix < arr1.Length; ++ix)
          if (arr1[ix] != arr2[ix]) return false;
        return true;
      }
    }
  }

您应该使用更强大的散列如果你把成千上万的阵列中的哈希表。检查这篇文章为例。

You should use a stronger hash if you put thousands of arrays in the hash table. Check this post for an example.

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