XmlAttributeOverrides 类

定义

允许在使用 XmlSerializer 串行化或反序列化对象时替代属性、字段和类特性。Allows you to override property, field, and class attributes when you use the XmlSerializer to serialize or deserialize an object.

public ref class XmlAttributeOverrides
public class XmlAttributeOverrides
type XmlAttributeOverrides = class
Public Class XmlAttributeOverrides
继承
XmlAttributeOverrides

示例

下面的示例对名为 Orchestra的类进行序列化,该类包含一个名为 Instruments 的字段,该字段返回 Instrument 对象的数组。The following example serializes a class named Orchestra, which contains a single field named Instruments that returns an array of Instrument objects. 名为 Brass 的第二个类继承自 Instrument 类。A second class named Brass inherits from the Instrument class. 该示例使用 XmlAttributeOverrides 类的实例重写 Instrument 字段,允许字段接受 Brass 对象。The example uses an instance of the XmlAttributeOverrides class to override the Instrument field, allowing the field to accept Brass objects.

#using <System.Xml.dll>
#using <System.dll>

using namespace System;
using namespace System::IO;
using namespace System::Xml::Serialization;

public ref class Instrument
{
public:
   String^ Name;
};

public ref class Brass: public Instrument
{
public:
   bool IsValved;
};

public ref class Orchestra
{
public:
   array<Instrument^>^Instruments;
};

void SerializeObject( String^ filename )
{
   /* Each overridden field, property, or type requires 
      an XmlAttributes object. */
   XmlAttributes^ attrs = gcnew XmlAttributes;

   /* Create an XmlElementAttribute to override the 
      field that returns Instrument objects. The overridden field
      returns Brass objects instead. */
   XmlElementAttribute^ attr = gcnew XmlElementAttribute;
   attr->ElementName = "Brass";
   attr->Type = Brass::typeid;

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

   // Create the XmlAttributeOverrides object.
   XmlAttributeOverrides^ attrOverrides = gcnew 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( Orchestra::typeid, "Instruments", attrs );

   // Create the XmlSerializer using the XmlAttributeOverrides.
   XmlSerializer^ s = gcnew XmlSerializer( Orchestra::typeid,attrOverrides );

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

   // Create the object that will be serialized.
   Orchestra^ band = gcnew Orchestra;

   // Create an object of the derived type.
   Brass^ i = gcnew Brass;
   i->Name = "Trumpet";
   i->IsValved = true;
   array<Instrument^>^myInstruments = {i};
   band->Instruments = myInstruments;

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

void DeserializeObject( String^ filename )
{
   XmlAttributeOverrides^ attrOverrides = gcnew XmlAttributeOverrides;
   XmlAttributes^ attrs = gcnew XmlAttributes;

   // Create an XmlElementAttribute to override the Instrument.
   XmlElementAttribute^ attr = gcnew XmlElementAttribute;
   attr->ElementName = "Brass";
   attr->Type = Brass::typeid;

   // Add the XmlElementAttribute to the collection of objects.
   attrs->XmlElements->Add( attr );
   attrOverrides->Add( Orchestra::typeid, "Instruments", attrs );

   // Create the XmlSerializer using the XmlAttributeOverrides.
   XmlSerializer^ s = gcnew XmlSerializer( Orchestra::typeid,attrOverrides );
   FileStream^ fs = gcnew FileStream( filename,FileMode::Open );
   Orchestra^ band = dynamic_cast<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;
   System::Collections::IEnumerator^ myEnum = band->Instruments->GetEnumerator();
   while ( myEnum->MoveNext() )
   {
      Instrument^ i = safe_cast<Instrument^>(myEnum->Current);
      b = dynamic_cast<Brass^>(i);
      Console::WriteLine( "{0}\n{1}", b->Name, b->IsValved );
   }
}

int main()
{
   SerializeObject( "Override.xml" );
   DeserializeObject( "Override.xml" );
}
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

使用 XmlAttributeOverridesXmlSerializer 可以重写序列化一组对象的默认方式。The XmlAttributeOverrides enables the XmlSerializer to override the default way of serializing a set of objects. 以这种方式重写序列化具有两个用途:首先,可以控制和增加在 DLL 中找到的对象的序列化(即使你无法访问源);其次,您可以创建一组可序列化类,但可以通过多种方式序列化这些对象。Overriding serialization in this way has two uses: first, you can control and augment the serialization of objects found in a DLL--even if you do not have access to the source; second, you can create one set of serializable classes, but serialize the objects in multiple ways. 例如,可以将类实例的成员作为 xml 属性进行序列化,而不是将其序列化为 xml 元素,从而使传输的文档更有效。For example, instead of serializing members of a class instance as XML elements, you can serialize them as XML attributes, resulting in a more efficient document to transport.

创建 XmlAttributeOverrides 对象后,可以将其作为参数传递到 XmlSerializer 构造函数。After you create an XmlAttributeOverrides object, you pass it as an argument to the XmlSerializer constructor. 生成的 XmlSerializer 使用 XmlAttributeOverrides 包含的数据重写控制如何序列化对象的特性。The resulting XmlSerializer uses the data contained by the XmlAttributeOverrides to override attributes that control how objects are serialized. 为实现此目的,XmlAttributeOverrides 包含被重写的对象类型的集合,以及与每个被重写的对象类型相关联的 XmlAttributes 对象。To accomplish this, the XmlAttributeOverrides contains a collection of the object types that are overridden, as well as an XmlAttributes object associated with each overridden object type. XmlAttributes 对象本身包含一组适当的属性对象,这些对象控制如何序列化每个字段、属性或类。The XmlAttributes object itself contains an appropriate set of attribute objects that control how each field, property, or class is serialized.

创建和使用 XmlAttributeOverrides 对象的过程如下所示:The process for creating and using an XmlAttributeOverrides object is as follows:

  1. 创建 XmlAttributes 对象。Create an XmlAttributes object.

  2. 创建适合要重写的对象的属性对象。Create an attribute object that is appropriate to the object being overridden. 例如,若要重写字段或属性,请使用新的派生类型创建 XmlElementAttributeFor example, to override a field or property, create an XmlElementAttribute, using the new, derived type. 您可以选择分配新的 ElementName或重写基类的属性名称或命名空间的 NamespaceYou can optionally assign a new ElementName, or Namespace that overrides the base class's attribute name or namespace.

  3. 将特性对象添加到相应的 XmlAttributes 属性或集合。Add the attribute object to the appropriate XmlAttributes property or collection. 例如,你可以将 XmlElementAttribute 添加到 XmlAttributes 对象的 XmlElements 集合,并指定要重写的成员名称。For example, you would add the XmlElementAttribute to the XmlElements collection of the XmlAttributes object, specifying the member name that is being overridden.

  4. 创建 XmlAttributeOverrides 对象。Create an XmlAttributeOverrides object.

  5. 使用 Add 方法,将 XmlAttributes 对象添加到 XmlAttributeOverrides 对象。Using the Add method, add the XmlAttributes object to the XmlAttributeOverrides object. 如果要重写的对象是 XmlRootAttributeXmlTypeAttribute,则只需指定重写的对象的类型。If the object being overridden is an XmlRootAttribute or XmlTypeAttribute, you need only to specify the type of the overridden object. 但如果要重写字段或属性,还必须指定重写成员的名称。But if you are overriding a field or property, you must also specify the name of the overridden member.

  6. 构造 XmlSerializer时,将 XmlAttributeOverrides 传递到 XmlSerializer 构造函数。When constructing the XmlSerializer, pass the XmlAttributeOverrides to the XmlSerializer constructor.

  7. 使用生成的 XmlSerializer 序列化或反序列化派生类对象。Use the resulting XmlSerializer to serialize or deserialize the derived class objects.

构造函数

XmlAttributeOverrides()

初始化 XmlAttributeOverrides 类的新实例。Initializes a new instance of the XmlAttributeOverrides class.

属性

Item[Type, String]

获取与指定(基类)类型相关联的对象。Gets the object associated with the specified (base-class) type. 成员参数指定被替代的基类成员。The member parameter specifies the base-class member that is overridden.

Item[Type]

获取与指定的基类类型相关联的对象。Gets the object associated with the specified, base-class, type.

方法

Add(Type, String, XmlAttributes)

XmlAttributes 对象添加到 XmlAttributes 对象的集合中。Adds an XmlAttributes object to the collection of XmlAttributes objects. type 参数指定要替代的对象。The type parameter specifies an object to be overridden. member 参数指定所替代的成员名称。The member parameter specifies the name of a member that is overridden.

Add(Type, XmlAttributes)

XmlAttributes 对象添加到 XmlAttributes 对象的集合中。Adds an XmlAttributes object to the collection of XmlAttributes objects. type 参数指定由 XmlAttributes 对象替代的对象。The type parameter specifies an object to be overridden by the XmlAttributes object.

Equals(Object)

确定指定对象是否等于当前对象。Determines whether the specified object is equal to the current object.

(继承自 Object)
GetHashCode()

用作默认哈希函数。Serves as the default hash function.

(继承自 Object)
GetType()

获取当前实例的 TypeGets the Type of the current instance.

(继承自 Object)
MemberwiseClone()

创建当前 Object 的浅表副本。Creates a shallow copy of the current Object.

(继承自 Object)
ToString()

返回表示当前对象的字符串。Returns a string that represents the current object.

(继承自 Object)

适用于

另请参阅