1 private void GetDicKeyByValue() 2         { 3             Dictionary
     
       dic = new Dictionary
      
       (); 4             dic.Add("1", "1"); 5             dic.Add("2", "2"); 6             dic.Add("3", "2"); 7             //foreach KeyValuePair traversing 8             foreach (KeyValuePair
       
         kvp in dic) 9             {10                 if (kvp.Value.Equals("2"))11                 { 12                     //...... kvp.Key;13                 }14             }15 16             //foreach dic.Keys17             foreach (string key in dic.Keys)18             {19                 if (dic[key].Equals("2"))20                 { 21                     //...... key22                 }23             }24 25             //Linq26             var keys = dic.Where(q => q.Value == "2").Select(q => q.Key);  //get all keys27 28             List
        
          keyList = (from q in dic29                                     where q.Value == "2"30                                     select q.Key).ToList
         
          (); //get all keys31 32             var firstKey = dic.FirstOrDefault(q => q.Value == "2").Key;  //get first key33         }