【C#】Dictionary通過value獲取對應的key值

通過key值獲取value值方法想必大家都知道

private void GetDicValueByKey()  
{  
            Dictionary<string, string> dic = new Dictionary<string, string>();  
            dic.Add("1", "1");  
            dic.Add("2", "2");  
            dic.Add("3", "2");  
            string value;
            dic.TryGetValue("2",out value);//......value
            
}

1：最直白的循環遍歷方法，可以分爲遍歷key--value鍵值對以及所有的key兩種表現形式

2：用Linq的方式去查詢（添加對應的命名空間：using System.Linq）

 如下爲一個十分簡單的代碼示例：

private void GetDicKeyByValue()  
        {  
            Dictionary<string, string> dic = new Dictionary<string, string>();  
            dic.Add("1", "1");  
            dic.Add("2", "2");  
            dic.Add("3", "2");  
            //foreach KeyValuePair traversing  
            foreach (KeyValuePair<string, string> kvp in dic)  
            {  
                if (kvp.Value.Equals("2"))  
                {   
                    //...... kvp.Key;  
                }  
            }  
  
            //foreach dic.Keys  
            foreach (string key in dic.Keys)  
            {  
                if (dic[key].Equals("2"))  
                {   
                    //...... key  
                }  
            }  
  
            //Linq 方法 
            var keys = dic.Where(q => q.Value == "2").Select(q => q.Key);  //get all keys  
  
            List<string> keyList = (from q in dic  
                                    where q.Value == "2"  
                                    select q.Key).ToList<string>(); //get all keys  
  
            var firstKey = dic.FirstOrDefault(q => q.Value == "2").Key;  //get first key  
        }