如何在C#中从TKey获取字典TValue？

Question

我宣布了字典obj.

Dictionary<string, string> aDict = new Dictionary<string, string>(); 
        aDict .Add("IP", "Host"); 

我记得,

表达式aDict[IP]可以返回值(Host).

现在,如果我走向相反的方向.

如何从价值中获取关键？aDict[Host]？

字典是否是C#中的单行道,只能从Key运行到Value？谢谢.

Answer 1

字典不是这样工作的,它们也不打算这样做.您将如何解决以下问题:

key = "1", value = "x",
key = "2", value = "x"

你可以这样做:

var keys = dict.Where(kvp => kvp.Value == someValue).Select(kvp => kvp.Key);
foreach(var key in keys) {
    Console.WriteLine(key);
}

但是如果你真的需要在键和值之间来回切换,你应该考虑将问题封装到双向映射中.这是一个非常简单的实现,您可以根据您的需求定制:

class TwoWayDictionary<TLeft, TRight> {
    IDictionary<TLeft, TRight> leftToRight = new Dictionary<TLeft, TRight>();
    IDictionary<TRight, TLeft> rightToLeft = new Dictionary<TRight, TLeft>();

    public void Add(TLeft left, TRight right) {
        if (leftToRight.ContainsKey(left)) {
            throw new InvalidOperationException("key left is duplicate");
        }
        if (rightToLeft.ContainsKey(right)) {
            throw new InvalidOperationException("key right is duplicate");
        }
        leftToRight.Add(left, right);
        rightToLeft.Add(right, left);
    }

    public bool TryGetRightByLeft(TLeft left, out TRight right) {
        return leftToRight.TryGetValue(left, out right);
    }

    public bool TryGetLeftByRight(out TLeft left, TRight right) {
        return rightToLeft.TryGetValue(right, out left);
    }
}

请注意,这假设没有密钥被复制.

现在你可以说:

TwoWayDictionary<string, string> dict = new TwoWayDictionary<string, string>();
dict.Add("127.0.0.1", "localhost");

string host;
dict.TryGetRightByLeft("127.0.0.1", out host);
// host is "localhost"

string ip;
dict.TryGetLeftByRight("localhost", out ip);
// ip is "127.0.0.1"