情境如下，我們定義一個抽象型別Notification保存排程發送通知的資料(包含JobType、ScheduleTime及Message)，依發送管道分為電子郵件通知及簡訊通知，故實作成EmailNotification及SMSNotification兩個類別，並各自增加Email及PhoneNo屬性。
using Newtonsoft.Json;using Newtonsoft.Json.Converters;using System;namespace CustCreate{publicenum Channels
{Email, SMS
}
//通知作業publicabstractclass Notification
{ [JsonConverter(typeof(StringEnumConverter))]//通知管道public Channels JobType { get; protected set; }
//排程時間public DateTime ScheduledTime { get; set; }//訊息內容publicstring Message { get; set; }
protected Notification(DateTime time, string msg)
{ScheduledTime = time;
Message = msg;
}
protected Notification() { }}
//電子郵件通知publicclass EmailNotification : Notification
{publicstring Email { get; set; }
public EmailNotification(DateTime time, string email, string msg)
: base(time, msg) {JobType = Channels.Email;
Email = email;
}
}
//簡訊通知publicclass SMSNotification : Notification
{//電話號碼publicstring PhoneNo { get; set; }
public SMSNotification() {JobType = Channels.SMS;
}
public SMSNotification(DateTime time, string phoneNo, string msg)
: base(time, msg) {JobType = Channels.SMS;
PhoneNo = phoneNo;
}
}
}
依循上述資料結構，我們可輕易產生一個List<Notification>，其中包含EmailNotification及SMSNotification兩種不同型別的物件，用JsonConvert.SerializeObject()簡單轉成JSON:
var jobs = new List<Notification>(); jobs.Add(new EmailNotification(DateTime.UtcNow, "blah@bubu.blah.boo", "Test 1"));
jobs.Add(new SMSNotification(DateTime.UtcNow, "0912345678", "Test 2"));
Console.WriteLine(
JsonConvert.SerializeObject(jobs, Formatting.Indented));
Console.Read();
產生JSON字串如下:
[
{"Email": "blah@bubu.blah.boo","JobType": "Email","ScheduledTime": "2013-12-13T13:43:25.6881876Z","Message": "Test 1"
},
{"PhoneNo": "0912345678","JobType": "SMS","ScheduledTime": "2013-12-13T13:43:25.6891803Z","Message": "Test 2"
}
]到目前為止非常輕鬆愉快吧? 然後呢? 以前學過的JsonConvert.DeserializeObject<T>都只能轉回單一型別，要怎麼把它反序列化還原回內含EmailNotification及SMSNotification不同型別物件的List<Notification>?
雖然不算常見情境，但這可難不倒偉大的Json.NET!
以下是程式範例，關鍵在於我們得繼承CustomCreationConverter<T>自訂一個轉換Notification物件的轉換器作為DesializeObject時的第二個參數。而在轉換器中可透過覆寫ReadJson()方法，依輸入JSON內容，傳回轉換後的物件。如此，我們就能依JobType動態建立不同型別的物件，再從JSON內容取得屬性值，達成反序列化還原出不同型別物件的目標。
另外，稍早定義物件時有預留伏筆，EmailNotification只提供有參數的建構式，而SMSNotification則支援無參數建構式(可沿用內建的屬性對應機制)，以便示範兩種不同做法，細節部分請直接看程式碼及註解。
using Newtonsoft.Json;using Newtonsoft.Json.Converters;using Newtonsoft.Json.Linq;using System;using System.Collections.Generic;namespace CustCreate{class Program {staticstring json = @"[
{""Email"": ""blah@bubu.blah.boo"",
""JobType"": ""Email"",
""ScheduledTime"": ""2013-12-13T13:43:25.6881876Z"",
""Message"": ""Test 1""
},
{""PhoneNo"": ""0912345678"",
""JobType"": ""SMS"",
""ScheduledTime"": ""2013-12-13T13:43:25.6891803Z"",
""Message"": ""Test 2""
}
]";
//自訂轉換器，繼承CustomCreationConverter<T>class NotificationConverter : CustomCreationConverter<Notification> {//由於ReadJson會依JSON內容建立不同物件，用不到Create()publicoverride Notification Create(Type objectType)
{thrownew NotImplementedException();
}
//自訂解析JSON傳回物件的邏輯publicoverrideobject ReadJson(JsonReader reader, Type objectType,
object existingValue, JsonSerializer serializer) {JObject jo = JObject.Load(reader);
//先取得JobType，由其決定建立物件string jobType = jo["JobType"].ToString();
if (jobType == "Email")
{//做法1: 由JObject取出建構式所需參數建構物件 var target = new EmailNotification( jo["ScheduledTime"].Value<DateTime>(), jo["Email"].ToString(), jo["Message"].ToString());
return target;}
elseif (jobType == "SMS")
{//做法2: 若物件支援無參數建構式，則可直接透過// serializer.Populate()自動對應屬性 var target = new SMSNotification();serializer.Populate(jo.CreateReader(), target);
return target;}
elsethrownew ApplicationException("Unsupported type: " + jobType);
}
}
staticvoid Main(string[] args)
{//JsonConvert.DeserializeObject時傳入自訂Convertervar list = JsonConvert.DeserializeObject<List<Notification>>(
json, new NotificationConverter());var item = list[0];
Console.WriteLine("Type:{0} Email={1}", item.JobType, (item as EmailNotification).Email);item = list[1];
Console.WriteLine("Type:{0} PhoneNo={1}", item.JobType, (item as SMSNotification).PhoneNo);Console.Read();
}
}
}
就醬，我們就從JSON完整重現原本的List<Notification>囉~
Type:Email Email=blah@bubu.blah.boo Type:SMS PhoneNo=0912345678