用switch case處理一個很長的判斷，例如56個民族01代表漢族，02代表藏族，03代表壯族...，當傳入數字想獲取民族名稱時就得寫56個case，當傳入民族獲取背後的數字時，又得再寫56個case，如下所示：

private string GetNationValue(string s)
{
    string result = "5";                      
    switch (s)
    {
        case "01":
            result = "漢族";
            break;
        case "02":
            result = "藏族";
            break;
        case "03":
            result = "壯族";
            break;
        case "04":
            result = "朝鮮族";
            break;
        //這裡省略其它......
    }         
    return result;
}
private string GetNationKey(string s)
{
    string result = "5";                      
    switch (s)
    {
        case "漢族":
            result = "01";
            break;
        case "藏族":
            result = "02";
            break;
        case "壯族":
            result = "03";
            break;
        case "朝鮮族":
            result = "04";
            break;
        //這裡省略其它......
    }         
    return result;
} 
 

這麼長的程式碼很醜陋，要修改也不容易，可以通過Dictionary來改進，鍵和值是成對寫在一起的，非常容易維護，改寫後代碼如下：

public enum FormatType
{
    GetKey,
    GetValue
}
public class Format
{
    private static string Get(Dictionary<string, string> dict, FormatType formatType, string code)
    {           
        if (formatType == FormatType.GetKey)
             return dict.FirstOrDefault(d => d.Value == code).Key;
        else
             return dict.FirstOrDefault(d => d.Key == code).Value;  
    }
    public static string GetNation(FormatType formatType, string code)
    {
       Dictionary<string, string> dict = new Dictionary<string, string>{  
                {"01","漢族"},
                {"02","藏族"},
                {"03","壯族"},
                {"04","朝鮮族"}
                //這裡省略其它......
        };
       return Get(dict, formatType, code);
   }
}
 

使用：
獲取"漢族"的編碼
string key = Format.GetNation(FormatType.GetKey, "漢族");
獲取"01"代表的民族
string value = Format.GetNation(FormatType.GetValue, "01");