C# Dictionary已知value擷取對應的key

標籤：

1：迴圈遍曆法，分為遍曆key-value索引值對和遍曆所有key兩種形式

2：使用Linq查詢法

 1     private void GetDictKeyByValue() 2     { 3         Dictionary<int, string> dict = new Dictionary<int, string>(); 4         dict.Add(1, "1"); 5         dict.Add(2, "2"); 6         dict.Add(3, "2"); 7         dict.Add(4, "4"); 8  9         // foreach KeyValuePair10         List<int> list = new List<int>();11         foreach (KeyValuePair<int, string> kvp in dict)12         {13             if (kvp.Value.Equals("2"))14             {15                 list.Add(kvp.Key); // kvp.Key;16             }17         }18 19         // foreach dic.Keys20         list.Clear();21         foreach (int key in dict.Keys)22         {23             if (dict[key].Equals("2"))24             {25                 list.Add(key); // key26             }27         }28 29         // Linq30         List<int> keyList = dict.Where(q => q.Value == "2")31                         .Select(q => q.Key).ToList<int>(); //get all keys32 33         keyList = (from q in dict34                     where q.Value == "2"35                     select q.Key).ToList<int>(); //get all keys36 37         var firstKey = dict.FirstOrDefault(q => q.Value == "2").Key; //get first key38     }

C# Dictionary已知value擷取對應的key