XmlAttributeOverrides 类

定义

命名空间:

System.Xml.Serialization

程序集:

netstandard.dll, System.Xml.XmlSerializer.dll

Source:

XmlAttributeOverrides.cs

允许在用于 XmlSerializer 序列化或反序列化对象时重写属性、字段和类属性。

public ref class XmlAttributeOverrides

public class XmlAttributeOverrides

type XmlAttributeOverrides = class

Public Class XmlAttributeOverrides

继承

Object

XmlAttributeOverrides

示例

以下示例序列化名为Orchestra的类，该类包含一个名为返回对象数组的Instrument单个字段Instruments。 名为 Brass 第二个类的继承自该 Instrument 类。 该示例使用类的 XmlAttributeOverrides 实例重写 Instrument 字段，从而允许该字段接受 Brass 对象。

using System;
using System.IO;
using System.Xml.Serialization;

public class Orchestra
{
   public Instrument[] Instruments;
}

public class Instrument
{
   public string Name;
}

public class Brass:Instrument
{
   public bool IsValved;
}

public class Run
{
    public static void Main()
    {
       Run test = new Run();
       test.SerializeObject("Override.xml");
       test.DeserializeObject("Override.xml");
    }

    public void SerializeObject(string filename)
    {
      /* Each overridden field, property, or type requires
      an XmlAttributes object. */
      XmlAttributes attrs = new XmlAttributes();

      /* Create an XmlElementAttribute to override the
      field that returns Instrument objects. The overridden field
      returns Brass objects instead. */
      XmlElementAttribute attr = new XmlElementAttribute();
      attr.ElementName = "Brass";
      attr.Type = typeof(Brass);

      // Add the element to the collection of elements.
      attrs.XmlElements.Add(attr);

      // Create the XmlAttributeOverrides object.
      XmlAttributeOverrides attrOverrides = new XmlAttributeOverrides();

      /* Add the type of the class that contains the overridden
      member and the XmlAttributes to override it with to the
      XmlAttributeOverrides object. */
      attrOverrides.Add(typeof(Orchestra), "Instruments", attrs);

      // Create the XmlSerializer using the XmlAttributeOverrides.
      XmlSerializer s =
      new XmlSerializer(typeof(Orchestra), attrOverrides);

      // Writing the file requires a TextWriter.
      TextWriter writer = new StreamWriter(filename);

      // Create the object that will be serialized.
      Orchestra band = new Orchestra();

      // Create an object of the derived type.
      Brass i = new Brass();
      i.Name = "Trumpet";
      i.IsValved = true;
      Instrument[] myInstruments = {i};
      band.Instruments = myInstruments;

      // Serialize the object.
      s.Serialize(writer,band);
      writer.Close();
   }

   public void DeserializeObject(string filename)
   {
      XmlAttributeOverrides attrOverrides =
         new XmlAttributeOverrides();
      XmlAttributes attrs = new XmlAttributes();

      // Create an XmlElementAttribute to override the Instrument.
      XmlElementAttribute attr = new XmlElementAttribute();
      attr.ElementName = "Brass";
      attr.Type = typeof(Brass);

      // Add the XmlElementAttribute to the collection of objects.
      attrs.XmlElements.Add(attr);

      attrOverrides.Add(typeof(Orchestra), "Instruments", attrs);

      // Create the XmlSerializer using the XmlAttributeOverrides.
      XmlSerializer s =
      new XmlSerializer(typeof(Orchestra), attrOverrides);

      FileStream fs = new FileStream(filename, FileMode.Open);
      Orchestra band = (Orchestra) s.Deserialize(fs);
      Console.WriteLine("Brass:");

      /* The difference between deserializing the overridden
      XML document and serializing it is this: To read the derived
      object values, you must declare an object of the derived type
      (Brass), and cast the Instrument instance to it. */
      Brass b;
      foreach(Instrument i in band.Instruments)
      {
         b = (Brass)i;
         Console.WriteLine(
         b.Name + "\n" +
         b.IsValved);
      }
   }
}

Option Explicit
Option Strict

Imports System.IO
Imports System.Xml.Serialization

Public Class Orchestra
    Public Instruments() As Instrument
End Class

Public Class Instrument
    Public Name As String
End Class

Public Class Brass
    Inherits Instrument
    Public IsValved As Boolean
End Class

Public Class Run
    
    Public Shared Sub Main()
        Dim test As New Run()
        test.SerializeObject("Override.xml")
        test.DeserializeObject("Override.xml")
    End Sub
        
    Public Sub SerializeObject(ByVal filename As String)
        ' Each overridden field, property, or type requires
        ' an XmlAttributes object. 
        Dim attrs As New XmlAttributes()
        
        ' Create an XmlElementAttribute to override the
        ' field that returns Instrument objects. The overridden field
        ' returns Brass objects instead. 
        Dim attr As New XmlElementAttribute()
        attr.ElementName = "Brass"
        attr.Type = GetType(Brass)
        
        ' Add the element to the collection of elements.
        attrs.XmlElements.Add(attr)
        
        ' Create the XmlAttributeOverrides object.
        Dim attrOverrides As New XmlAttributeOverrides()
        
        ' Add the type of the class that contains the overridden
        ' member and the XmlAttributes to override it with to the
        ' XmlAttributeOverrides object. 
        attrOverrides.Add(GetType(Orchestra), "Instruments", attrs)
        
        ' Create the XmlSerializer using the XmlAttributeOverrides.
        Dim s As New XmlSerializer(GetType(Orchestra), attrOverrides)
        
        ' Writing the file requires a TextWriter.
        Dim writer As New StreamWriter(filename)
        
        ' Create the object that will be serialized.
        Dim band As New Orchestra()
        
        ' Create an object of the derived type.
        Dim i As New Brass()
        i.Name = "Trumpet"
        i.IsValved = True
        Dim myInstruments() As Instrument = {i}
        band.Instruments = myInstruments
        
        ' Serialize the object.
        s.Serialize(writer, band)
        writer.Close()
    End Sub    
    
    Public Sub DeserializeObject(filename As String)
        Dim attrOverrides As New XmlAttributeOverrides()
        Dim attrs As New XmlAttributes()
        
        ' Create an XmlElementAttribute to override the Instrument.
        Dim attr As New XmlElementAttribute()
        attr.ElementName = "Brass"
        attr.Type = GetType(Brass)
        
        ' Add the XmlElementAttribute to the collection of objects.
        attrs.XmlElements.Add(attr)
        
        attrOverrides.Add(GetType(Orchestra), "Instruments", attrs)
        
        ' Create the XmlSerializer using the XmlAttributeOverrides.
        Dim s As New XmlSerializer(GetType(Orchestra), attrOverrides)
        
        Dim fs As New FileStream(filename, FileMode.Open)
        Dim band As Orchestra = CType(s.Deserialize(fs), Orchestra)
        Console.WriteLine("Brass:")
        
        ' The difference between deserializing the overridden
        ' XML document and serializing it is this: To read the derived
        ' object values, you must declare an object of the derived type
        ' (Brass), and cast the Instrument instance to it. 
        Dim b As Brass
        Dim i As Instrument
        For Each i In  band.Instruments
            b = CType(i, Brass)
            Console.WriteLine(b.Name & ControlChars.Cr & b.IsValved)
        Next i
    End Sub
End Class

注解

这样 XmlAttributeOverrides ， XmlSerializer 便可以替代序列化一组对象的默认方式。 以这种方式重写序列化有两个用途：首先，可以控制并增强 DLL 中找到的对象序列化，即使你无权访问源：其次，可以创建一组可序列化类，但以多种方式序列化对象。 例如，可以将它们序列化为 XML 属性，而不是将类实例的成员序列化为 XML 属性，从而生成更高效的文档进行传输。

创建对象 XmlAttributeOverrides 后，将其作为参数 XmlSerializer 传递给构造函数。 生成的 XmlSerializer 数据使用包含 XmlAttributeOverrides 的数据替代控制对象序列化方式的属性。 为此，该 XmlAttributeOverrides 对象包含被重写的对象类型的集合，以及 XmlAttributes 与每个重写的对象类型关联的对象。 对象 XmlAttributes 本身包含一组适当的属性对象，用于控制如何序列化每个字段、属性或类。

创建和使用 XmlAttributeOverrides 对象的过程如下所示：

1. 创建一个 XmlAttributes 对象。

2. 创建一个适合被重写的对象的属性对象。 例如，若要重写字段或属性，请使用新的派生类型创建一个 XmlElementAttribute。 可以选择分配一个新 ElementName项，也可以 Namespace 替代基类的属性名称或命名空间。

3. 将特性对象添加到相应的 XmlAttributes 属性或集合。 例如，将对象集合添加到XmlElementAttributeXmlElements对象集合XmlAttributes，并指定要重写的成员名称。

4. 创建一个 XmlAttributeOverrides 对象。

5. 使用该方法Add将对象添加到XmlAttributesXmlAttributeOverrides对象。 如果被重写的对象是或XmlRootAttributeXmlTypeAttribute，则只需指定重写对象的类型。 但是，如果要重写字段或属性，则还必须指定重写成员的名称。

6. 构造XmlSerializer时，将XmlAttributeOverridesXmlSerializer传递给构造函数。

7. 使用生成的 XmlSerializer 对派生类对象进行序列化或反序列化。

构造函数

名称	说明
XmlAttributeOverrides()	初始化 XmlAttributeOverrides 类的新实例。

属性

名称	说明
Item[Type, String]	获取与指定（基类）类型关联的对象。 成员参数指定被重写的基类成员。
Item[Type]	获取与指定基类类型关联的对象。

方法

名称	说明
Add(Type, String, XmlAttributes)	将对象 XmlAttributes 添加到对象的集合 XmlAttributes 中。 该 type 参数指定要重写的对象。 该 member 参数指定被重写的成员的名称。
Add(Type, XmlAttributes)	将对象 XmlAttributes 添加到对象的集合 XmlAttributes 中。 该 type 参数指定要由 XmlAttributes 该对象重写的对象。
Equals(Object)	确定指定的对象是否等于当前对象。 (继承自 Object)
GetHashCode()	用作默认哈希函数。 (继承自 Object)
GetType()	获取当前实例的 Type。 (继承自 Object)
MemberwiseClone()	创建当前 Object的浅表副本。 (继承自 Object)
ToString()	返回一个表示当前对象的字符串。 (继承自 Object)

另请参阅

• Deserialize(Stream)
• Serialize(TextWriter, Object)
• XmlSerializer
• XmlAttributes
• XML 序列化简介
• 如何：为 XML 流指定备用元素名称
• 使用属性控制 XML 序列化
• XML 序列化示例
• XML 架构定义工具 (Xsd.exe)