Collection主要是指像Array, ArrayList, List, Dictionary, HashTable这些数据类型，大家平时用的很多。如果一个类中有一个Collection类型的成员，在对这个类进行XML序列化的时候，应该如何处理？应该说在.net当中这是比较简单的，只要建立一个XmlSerializer类就可以帮你自动搞定，不过有的时候你可能需要对自动的序列化过程施加更多的控制，比如XML的结构是实现固定的，你必须按照要求去生成XML结构。
使用不同的属性可以灵活的控制生成的XML，这里我就不多介绍了，主要讲一下如何序列化比较复杂的Collection结构。下面的方法，对于所有实现了IEnumerable接口的Collection都有效。
我使用MSDN中的例子，不过没有使用数组或者ArrayList，而是使用了比较高级的数据类型List<T>，希望在讲解如何序列化XML的同时给使用List<T>的同学提供点参考。
序列化一个List<T>
下面的代码示范了如何序列化一个List<T>，实际上和序列化其它类一样，把这个类扔给Serialize（）函数即可。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml.Serialization;
using System.IO;
namespace SerializeCollection
{
class Program
{
static void Main(string[] args)
{
Program test = new Program();
test.SerializeDocument("e:\\books.xml");
}
public void SerializeDocument(string filename)
{
// Creates a new XmlSerializer.
XmlSerializer s =
new XmlSerializer(typeof(MyRootClass));
// Writing the file requires a StreamWriter.
TextWriter myWriter = new StreamWriter(filename);
// Creates an instance of the class to serialize.
MyRootClass myRootClass = new MyRootClass();
//create items
Item item1 = new Item();
// Sets the objects' properties.
item1.ItemName = "Widget1";
item1.ItemCode = "w1";
item1.ItemPrice = 231;
item1.ItemQuantity = 3;
Item item2 = new Item();
// Sets the objects' properties.
item2.ItemName = "Widget2";
item2.ItemCode = "w2";
item2.ItemPrice = 800;
item2.ItemQuantity = 2;
// Sets the class's Items property to the list.
myRootClass.Items.Add(item1);
myRootClass.Items.Add(item2);
/* Serializes the class, writes it to disk, and closes
the TextWriter. */
s.Serialize(myWriter, myRootClass);
myWriter.Close();
}
}
// This is the class that will be serialized.
[Serializable]
public class MyRootClass
{
public MyRootClass()
{
items = new List<Item>();
}
private List<Item> items;
public List<Item> Items
{
get { return items; }
set { items = value; }
}
}
public class Item
{
[XmlElement(ElementName = "OrderItem")]
public string ItemName;
public string ItemCode;
public decimal ItemPrice;
public int ItemQuantity;
}
}
最后序列化成的XML：
<?xml version="1.0" encoding="utf-8"?>
<MyRootClass xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<Items>
<Item>
<OrderItem>Widget1</OrderItem>
<ItemCode>w1</ItemCode>
<ItemPrice>231</ItemPrice>
<ItemQuantity>3</ItemQuantity>
</Item>
<Item>
<OrderItem>Widget2</OrderItem>
<ItemCode>w2</ItemCode>
<ItemPrice>800</ItemPrice>
<ItemQuantity>2</ItemQuantity>
</Item>
</Items>
</MyRootClass>
如果这个List<T>中的成员的类还有继承关系
现在把情况变得复杂一点，因为多态，List<T>中的类可能是指定类型的子类型，这个时候会出现什么情况呢？
我们增加一个BookItem类，继承自Item 类。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml.Serialization;
using System.IO;
namespace SerializeCollection
{
class Program
{
static void Main(string[] args)
{
Program test = new Program();
test.SerializeDocument("e:\\books.xml");
}
public void SerializeDocument(string filename)
{
// Creates a new XmlSerializer.
XmlSerializer s =
new XmlSerializer(typeof(MyRootClass));
// Writing the file requires a StreamWriter.
TextWriter myWriter = new StreamWriter(filename);
// Creates an instance of the class to serialize.
MyRootClass myRootClass = new MyRootClass();
/* Uses a more advanced method of creating an list:
create instances of the Item and BookItem, where BookItem
is derived from Item. */
Item item1 = new Item();
// Sets the objects' properties.
item1.ItemName = "Widget1";
item1.ItemCode = "w1";
item1.ItemPrice = 231;
item1.ItemQuantity = 3;
BookItem bookItem = new BookItem();
// Sets the objects' properties.
bookItem.ItemCode = "w2";
bookItem.ItemPrice = 123;
bookItem.ItemQuantity = 7;
bookItem.ISBN = "34982333";
bookItem.Title = "Book of Widgets";
bookItem.Author = "John Smith";
// Sets the class's Items property to the list.
myRootClass.Items.Add(item1);
myRootClass.Items.Add(bookItem);
/* Serializes the class, writes it to disk, and closes
the TextWriter. */
s.Serialize(myWriter, myRootClass);
myWriter.Close();
}
}
// This is the class that will be serialized.
[Serializable]
public class MyRootClass
{
public MyRootClass()
{
items = new List<Item>();
}
private List<Item> items;
public List<Item> Items
{
get { return items; }
set { items = value; }
}
}
public class Item
{
[XmlElement(ElementName = "OrderItem")]
public string ItemName;
public string ItemCode;
public decimal ItemPrice;
public int ItemQuantity;
}
}
修改代码后，我们再运行，出现如下错误“不应是类型 SerializeCollection.BookItem。使用 XmlInclude 或 SoapInclude 属性静态指定非已知的类型”，看来是系统在做序列化的时候，搞不清楚List中的成员到底是什么类型。这个时候就要使用XmlArrayItem来帮忙了。MyRootClass类的Item成员前加入XmlArrayItem标志。
[XmlArrayItem(ElementName= "Item",
IsNullable=true,
Type = typeof(Item),
Namespace = "http://www.aboutdnn.com"),
XmlArrayItem(ElementName = "BookItem",
IsNullable = true,
Type = typeof(BookItem),
Namespace = http://www.aboutdnn.com)]
修改后的代码如下：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml.Serialization;
using System.IO;
namespace SerializeCollection
{
class Program
{
static void Main(string[] args)
{
Program test = new Program();
test.SerializeDocument("e:\\books.xml");
}
public void SerializeDocument(string filename)
{
// Creates a new XmlSerializer.
XmlSerializer s =
new XmlSerializer(typeof(MyRootClass));
// Writing the file requires a StreamWriter.
TextWriter myWriter = new StreamWriter(filename);
// Creates an instance of the class to serialize.
MyRootClass myRootClass = new MyRootClass();
/* Uses a more advanced method of creating an list:
create instances of the Item and BookItem, where BookItem
is derived from Item. */
Item item1 = new Item();
// Sets the objects' properties.
item1.ItemName = "Widget1";
item1.ItemCode = "w1";
item1.ItemPrice = 231;
item1.ItemQuantity = 3;
BookItem bookItem = new BookItem();
// Sets the objects' properties.
bookItem.ItemCode = "w2";
bookItem.ItemPrice = 123;
bookItem.ItemQuantity = 7;
bookItem.ISBN = "34982333";
bookItem.Title = "Book of Widgets";
bookItem.Author = "John Smith";
// Sets the class's Items property to the list.
myRootClass.Items.Add(item1);
myRootClass.Items.Add(bookItem);
/* Serializes the class, writes it to disk, and closes
the TextWriter. */
s.Serialize(myWriter, myRootClass);
myWriter.Close();
}
}
// This is the class that will be serialized.
[Serializable]
public class MyRootClass
{
public MyRootClass()
{
items = new List<Item>();
}
private List<Item> items;
public List<Item> Items
{
get { return items; }
set { items = value; }
}
}
public class Item
{
[XmlElement(ElementName = "OrderItem")]
public string ItemName;
public string ItemCode;
public decimal ItemPrice;
public int ItemQuantity;
}
public class BookItem : Item
{
public string Title;
public string Author;
public string ISBN;
}
}
序列化后的XML如下：
<?xml version="1.0" encoding="utf-8"?> <MyRootClass xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Items> <Item xmlns="http://www.aboutdnn.com"> <OrderItem>Widget1</OrderItem> <ItemCode>w1</ItemCode> <ItemPrice>231</ItemPrice> <ItemQuantity>3</ItemQuantity> </Item> <BookItem xmlns="http://www.aboutdnn.com"> <ItemCode>w2</ItemCode> <ItemPrice>123</ItemPrice> <ItemQuantity>7</ItemQuantity> <Title>Book of Widgets</Title> <Author>John Smith</Author> <ISBN>34982333</ISBN> </BookItem> </Items> </MyRootClass>
可以看到，已经根据不同的数据类型，序列化为不同名字的节点。这个时候，如果你还想修改XML中<Items>节点的名字或者添加属性，XmlArrayAttribute可以帮你的忙，这个你可以自己试试。
参考文档：
XmlArrayAttribute Class：http://msdn.microsoft.com/en-us/library/system.xml.serialization.xmlarrayattribute.aspx
对于所有控制XML序列化的Attributes，请参考这里：Attributes That Control XML Serialization
