为什么我的词典包含两个具有相同键的条目? [英] Why does my dictionary contain two entries with identical keys?

问题描述

我这样创建了字典:

Dictionary<byte[], MyClass> dic = new Dictionary<byte[], MyClass>();

假定密钥为20个字节的SHA1哈希.因此，在将两个条目添加到该字典中之后，我与调试器进行了检查，并且它们都具有相同的字节数组键.

the key is assumed to be a SHA1 hash of 20 bytes. So after having added two entries into that dictionary I checked with a debugger and both have the same byte array keys.

我以为字典不能做到这一点?

I thought dictionaries cannot do that?

PS:这是我添加它们的方式:

PS: Here's how I add them:

string strText1 = "text";

SHA1 sha1_1 = new SHA1CryptoServiceProvider();
byte[] bytesHash1 = sha1_1.ComputeHash(System.Text.Encoding.UTF8.GetBytes(strText1));

string strText2 = "text";

SHA1 sha1_2 = new SHA1CryptoServiceProvider();
byte[] bytesHash2 = sha1_2.ComputeHash(System.Text.Encoding.UTF8.GetBytes(strText2));

dic.Add(bytesHash1, 1);
dic.Add(bytesHash2, 2);

推荐答案

字典不能(具有重复的键).

Dictionaries can't do that (have duplicate keys).

但是，您的词典没有具有重复的键，因为比较器将byte[]视为引用，有效地使用了指针而不是数组的内容.

However, your dictionary doesn't have duplicate keys, because the comparator will treat byte[] as a reference, effectively using the pointer rather than the content of the array.

如果要使用byte[]作为键，可能最简单的解决方案是提供您自己的比较类，该类检查内容而不是参考值，例如:

If you want to use byte[] as the key, probably the easiest solution is to provide your own comparison class which checks the content rather than the reference value, something like:

public class BaComp: IEqualityComparer<byte[]> {
    public bool Equals (byte[] left, byte[] right) {
        // Handle case where one or both is null (equal only if both are null).

        if ((left == null) || (right == null))
            return (left == right);

        // Otherwise compare array sequences of two non-null array refs.

        return left.SequenceEqual (right);
    }

    public int GetHashCode (byte[] key) {
        // Complain bitterly if null reference.

        if (key == null)
            throw new ArgumentNullException ();

        // Otherwise just sum bytes in array (one option, there are others).

        int rc = 0;
        foreach (byte b in key)
            rc += b;
        return rc;
    }
}

然后像这样使用它:

Dictionary<byte[], MyClass> dic = new Dictionary<byte[], MyClass> (new BaComp());

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