解惑 DataContractSerializer 数据契约序列器（2）
接着上一篇。
代码
代码
在这个时候我们可以提出这样一个问题了：为什么两个序列器输出的结果会这样不一样呢？其实，它们两者没有什么可比性 的，DataContractSerializer 的出现并不是为了代替XmlSerializer，而是为了WCF提供一个高效的序列化工具，而且他只是序列化出XmlContent，也就是说它的结果 只有xml的内容部分，并且这些内容能够被 C#中操作xml各个类所识别的（详细参考：http://z.xiaoi.com/r?msdn.microsoft.com%2Fzh- cn%2Flibrary%2Fsystem.runtime.serialization.datacontractserializer.aspx）
继续看下面一段代码。
代码
1
[Test]
2 public void Test3()
3
{
4
List<Person> list = new List<Person>();
5
6
list.Add(new Person { ID = "1", FirstName = "Lee", LastName = "Jetson" });
7 list.Add(new Person { ID = "1", FirstName = "Chen", LastName = "Mc" });
8 list.Add(new Person { ID = "1", FirstName = "He", LastName = "James" });
9
10 var ser = new DataContractSerializer(typeof(List<Person>));
11 var ms = new MemoryStream();
12 var writer = XmlDictionaryWriter.CreateTextWriter(ms);
13 ser.WriteObject(writer, list);
14 writer.Close();
15 string xml = Encoding.UTF8.GetString(ms.ToArray());
16 Console.WriteLine(xml);
17
}
[Test]2
public void Test3()3
{
4
List<Person> list = new List<Person>();5
6
list.Add(new Person { ID = "1", FirstName = "Lee", LastName = "Jetson" });
list.Add(7
list.Add(new Person { ID = "1", FirstName = "Chen", LastName = "Mc" });8
list.Add(new Person { ID = "1", FirstName = "He", LastName = "James" });9
10
var ser = new DataContractSerializer(typeof(List<Person>));11
var ms = new MemoryStream();12
var writer = XmlDictionaryWriter.CreateTextWriter(ms);13
ser.WriteObject(writer, list);14
writer.Close();15
string xml = Encoding.UTF8.GetString(ms.ToArray());16
Console.WriteLine(xml);17
}
输出结果同样是没有 <?xml version="1.0" encoding="utf-8"?>这一个标记。在微软官方的说法是XmlDictionaryWriter是经过优化的xmlwriter，究竟优化是原理这里就不做讨论了。
到这里，会有一个疑问：DataContractSerializer 序列器不是可以序列化出所要的内容吗，而且能被作为xm源在程序中读出？这样一想好像也是。不过有些时候我们的应用程序不一定只用c#语言编写，可能前台 是javascript或flex的话这样的输出结果就没办法操作了（例如，flex通过请求得出xml就会无法识别）。
继续下面一段代码：
代码 1 [Test]
2 public void Test4()
3 {
4 List<Person> list = new List<Person>();
5 list.Add(new Person { ID = "1", FirstName = "Lee", LastName = "Jetson" });
6 list.Add(new Person { ID = "1", FirstName = "Chen", LastName = "Mc" });
7 list.Add(new Person { ID = "1", FirstName = "He", LastName = "James" });
8
9 DataContractSerializer ser = new DataContractSerializer(typeof(List<Person>));
10 MemoryStream ms = new MemoryStream();
11 XmlWriter writer = XmlWriter.Create(ms);
12
13 ser.WriteObject(writer, list);
14 writer.Flush();
15 writer.Close();
16 string xml = Encoding.UTF8.GetString(ms.ToArray());
17 Console.WriteLine(xml);
18 }
[Test]2
public void Test4()3
{4
List<Person> list = new List<Person>();5
list.Add(new Person { ID = "1", FirstName = "Lee", LastName = "Jetson" });6
list.Add(new Person { ID = "1", FirstName = "Chen", LastName = "Mc" });7
list.Add(new Person { ID = "1", FirstName = "He", LastName = "James" });8
9
DataContractSerializer ser = new DataContractSerializer(typeof(List<Person>));10
MemoryStream ms = new MemoryStream();11
XmlWriter writer = XmlWriter.Create(ms);12
13
ser.WriteObject(writer, list);14
writer.Flush();15
writer.Close();16
string xml = Encoding.UTF8.GetString(ms.ToArray());17
Console.WriteLine(xml);18
}粗劣一看和Test4好像一样的，其实唯一的不同就是这里用的是XmlWriter 来写xml。输出结果竟然就会有<?xml version="1.0" encoding="utf-8"?>这一个标记。为什么？
