這邊就以Google API裡有段JSON字串當作練習怎麼產生：
以下整理幾種我見過的方式(個人推薦的放在最後^_^)
1. 字串拼接
最麻煩的方式，可讀性也差，若遇到Boolean型別的變數要記得轉小寫
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)//Get Method
{
//準備資料
string collapse_key = "score_update";
int time_to_live = 108;
bool delay_while_idle = true;
string score = "4x8";
string time = "15:16.2342";
List<string> registration_ids = new List<string>() { "4","8","15","16","23","42"};
//開始拼接字串
StringBuilder sb = new StringBuilder();
sb.AppendLine("{");
sb.AppendLine("\"collapse_key\":\""+collapse_key+"\",");
sb.AppendLine("\"time_to_live\":"+time_to_live+",");
sb.AppendLine("\"delay_while_idle\":"+delay_while_idle.ToString().ToLower()+",");
sb.AppendLine("\"data\":{");
sb.AppendLine("\"score\":\""+score+"\",");
sb.AppendLine("\"time\":\""+time+"\"");
sb.AppendLine("},");
sb.AppendLine("\"registration_ids\":[");
foreach (string item in registration_ids)
{
sb.Append("\""+item+"\",");
}
sb = new StringBuilder(sb.ToString().TrimEnd(','));//移除最後一個「,」字元
sb.AppendLine("]");
sb.AppendLine("}");
//輸出結果
Response.Write(sb.ToString());
}
}
↑所以很多人會尋找第三方套件來處理吧
以下便介紹Json.net，因為威力太強大了~
有了Json.net後就可以使用Json.net的函數產生JSON字串
2. 使用
JsonTextWriter用法很像XmlTextWriter，寫起來有點囉嗦，平常工作我不會用這個
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)//Get Method
{
//準備資料
string collapse_key = "score_update";
int time_to_live = 108;
bool delay_while_idle = true;
string score = "4x8";
string time = "15:16.2342";
List<string> registration_ids = new List<string>() { "4","8","15","16","23","42"};
//要輸出的變數
StringWriter sw = new StringWriter();
//建立JsonTextWriter
JsonTextWriter writer = new JsonTextWriter(sw);
writer.WriteStartObject();
writer.WritePropertyName("collapse_key"); writer.WriteValue(collapse_key);
writer.WritePropertyName("time_to_live"); writer.WriteValue(time_to_live);
writer.WritePropertyName("delay_while_idle"); writer.WriteValue(delay_while_idle);
writer.WritePropertyName("data");
writer.WriteStartObject();
writer.WritePropertyName("score"); writer.WriteValue(score);
writer.WritePropertyName("time"); writer.WriteValue(time);
writer.WriteEndObject();
writer.WritePropertyName("registration_ids");
writer.WriteStartArray();
foreach (string item in registration_ids)
{
writer.WriteValue(item);
}
writer.WriteEndArray();
writer.WriteEndObject();
//輸出結果
Response.Write(sw.ToString());
}
}
3. 使用JObject匿名物件
比起JsonTextWriter簡化了許多，不過大概是每個Property和值都要再寫一次建構子名稱，我覺得還是有點麻煩
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)//Get Method
{
//準備資料
string collapse_key = "score_update";
int time_to_live = 108;
bool delay_while_idle = true;
string score = "4x8";
string time = "15:16.2342";
List<string> registration_ids = new List<string>() { "4","8","15","16","23","42"};
//JObject匿名物件
JObject obj = new JObject(
new JProperty("collapse_key",collapse_key),
new JProperty("time_to_live",time_to_live),
new JProperty("delay_while_idle",delay_while_idle),
new JProperty("data",
new JObject(
new JProperty("score",score),
new JProperty("time",time))),
new JProperty("registration_ids",registration_ids)
);
//序列化為JSON字串並輸出結果
Response.Write(JsonConvert.SerializeObject(obj,Formatting.Indented));
}
}
那有沒有寫起來直覺，程式碼又短少的方式呢？
請看以下兩個
4. 物件序列化
這個要先知道輸出的json字串長什麼樣子
貼到http://json2csharp.com/去產生類別程式碼
然後
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)//Get Method
{
//準備資料
string collapse_key = "score_update";
int time_to_live = 108;
bool delay_while_idle = true;
string score = "4x8";
string time = "15:16.2342";
List<string> registration_ids = new List<string>() { "4","8","15","16","23","42"};
//建立物件，塞資料
RootObject root = new RootObject();
root.collapse_key = collapse_key;
root.time_to_live = time_to_live;
root.delay_while_idle = delay_while_idle;
Data data = new Data();
root.data = data;
root.data.score = score;
root.data.time = time;
root.registration_ids = registration_ids;
//物件序列化
string strJson = JsonConvert.SerializeObject(root, Formatting.Indented);
//輸出結果
Response.Write(strJson);
}
}
或使用物件初始化方式塞值
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)//Get Method
{
//準備資料
string collapse_key = "score_update";
int time_to_live = 108;
bool delay_while_idle = true;
string score = "4x8";
string time = "15:16.2342";
List<string> registration_ids = new List<string>() { "4","8","15","16","23","42"};
//建立物件，塞資料
RootObject root = new RootObject()
{
collapse_key = collapse_key,
time_to_live = time_to_live,
delay_while_idle = delay_while_idle,
data = new Data()
{
score = score,
time=time
},
registration_ids = registration_ids
};
//物件序列化
string strJson = JsonConvert.SerializeObject(root, Formatting.Indented);
//輸出結果
Response.Write(strJson);
}
}
使用物件初始化方式塞值看起來直覺多了
不過為了物件序列化還要特地宣告類別，這…倒不如使用Linq吧
5.用Linq+匿名物件寫法 直接組JSON
這招在Json.net的官方文件有範例(用JObject.FromObject的那個)：http://james.newtonking.com/projects/json/help/html/CreatingLINQtoJSON.htm
但只有範例，沒寫為什麼Linq要那樣寫，誰看得懂阿XD
要用Linq直接組JSON
大概把握幾點：
Json Object：Json字串用大括號{}表示，Linq也是用大括號{}表示
Json Object的Name(Key、Property)：Json字串在兩個雙引號””裡寫一個英文單字，Linq就直接寫英文單字即可
Json Array：Json字串用中括號[]表示，Linq就用from o in XXX select o，這種回傳IEnumerable的寫法(如果JSON字串是物件陣列的話就用from o in XXX select new {欄位1=YYY}這種形式)
Json Value：Linq就看Json字串填什麼值就跟著填什麼值
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)//Get Method
{
//準備資料
List<string> registration_ids = new List<string>() { "4", "8", "15", "16", "23", "42" };
//用Linq直接組
var result = new
{
collapse_key = "score_update",
time_to_live = 108,
delay_while_idle = true,
data = new{
score ="4x8",
time = "15:16.2342"
},
registration_ids = from s in registration_ids
select s
};
//序列化為JSON字串並輸出結果
Response.Write(JsonConvert.SerializeObject(result));
}
}
請看圖示解說↓
由於Linq支援DataTable的查詢，所以再難的JSON格式都組得出來，不用再跑for迴圈寫一堆Code，開發速度大幅提昇
以下截自實務上的一段Code(有做了一點修改)
DataTable dt = new DataTable();//撈出一張資料表的所有數據(這個表類似北風資料庫的員工資料表，有階層關係)
DataTable dtDetail = new DataTable();//上一張表的一對多明細表
var firstLevel = dt.Select("pid is NULL");//第一層數據
var result = new
{
Info = new
{
Level1 = from a in firstLevel
join b in dt.AsEnumerable() on a.Field<int>("id") equals b.Field<int?>("pid") into secondLevel
select new
{
Title = a.Field<string>("Title"),
Level2 = secondLevel.Select(c => new
{
Title = c.Field<string>("Title"),
Photos = from s in secondLevel
join uu in dtDetail.AsEnumerable() on s.Field<int>("id") equals uu.Field<int>("id")
where s.Field<int>("id") == c.Field<int>("id")
select new
{
PhotoID = uu.Field<string>("PhotoID"),
PhotoTitle = uu.Field<string>("PhotoTitle")
}
})
}
}
};
※不過要注意對於寫的人是寫很快，後人維護會有閱讀困難的可能
最後附上一張比較圖
2012.11.09 追記
最後一個方法，直接使用Linq產生Json字串有個缺點要提一下
Linq匿名型別的屬性無法給null值，如下圖
from : https://dotblogs.com.tw/shadow/archive/2012/08/16/74099.aspx
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