關於Dictionary的TryGetValue方法

這個方法時常會用到，而且很有效。TryGetValue：獲取與指定的鍵相關聯的值

比如我們讀取一個xml文件，讓後將其寫入到Dictionary中存儲：

private static Dictionary<string, string> SqlKeyValues = null;
       /// <summary>
       /// 必要用戶字段及別名
       /// </summary>
       internal static void InitUserFields(XmlDocument xml)
       {
           LoadXml(xml);

           XmlNode fields = xml.SelectSingleNode("/configs/users/fields");
           UserFields = new Dictionary<string, string>();
           if (fields.ChildNodes.Count > 0)
           {
               foreach (XmlNode n in fields.ChildNodes)
               {
                   if (n.NodeType != XmlNodeType.Comment && n.Name.ToLower() == "item")
                   {
                       XmlAttribute fieldName = n.Attributes["name"];
                       UserFields.Add(fieldName.Value, n.InnerXml);
                   }
               }
           }
       }

我們可以通過下面方面來獲取對應key的值

public static string GetUserField(string fieldName)
       {
           string finfo = "";
           UserFields.TryGetValue(fieldName, out finfo);
           return finfo;
       }

(bool)(UserFields.TryGetValue(fieldName, out finfo))可將其轉爲boo類型，它方便的是避免了判斷key知否存在而引發“給定關鍵字不在字典中。”的錯誤。可以通過下面的測試來更進一步瞭解：

Dictionary<string, string> dic = new Dictionary<string, string>();
            dic.Add("aaa", "123");
            dic.Add("bbb", "456");
            dic.Add("ccc", "789");
            dic.Add("ddd", "321");

            string outStr = "999";
            dic.TryGetValue("ttt", out outStr);
            Response.Write(outStr + "<br />");
            dic.TryGetValue("bbb", out outStr);
            Response.Write(outStr + "<br />");
            //Response.Write(dic["ttt"] + "<br />");