XmlAttributeOverrides 類別

定義

命名空間:

System.Xml.Serialization

組件:

System.Xml.XmlSerializer.dll

組件:

System.Xml.dll

組件:

netstandard.dll

當使用 XmlSerializer 來序列化或還原序列化物件時，允許您覆寫屬性 (Property)、欄位和類別屬性 (Attribute)。

public ref class XmlAttributeOverrides

public class XmlAttributeOverrides

type XmlAttributeOverrides = class

Public Class XmlAttributeOverrides

繼承

Object

XmlAttributeOverrides

範例

下列範例會序列化名為 的 Orchestra 類別，其中包含名為 的單一欄位，該欄位會 Instruments 傳回 物件的陣列 Instrument 。 名為 Brass 的第二個類別繼承自 Instrument 類別。 此範例會使用 類別的 XmlAttributeOverrides 實例來覆寫 Instrument 欄位，允許欄位接受 Brass 物件。

#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

備註

可 XmlAttributeOverrides 讓 XmlSerializer 覆寫序列化一組物件的預設方式。 以這種方式覆寫序列化有兩個用途：首先，您可以控制並增強 DLL 中找到的物件序列化，即使您沒有來源的存取權也一樣;其次，您可以建立一組可序列化的類別，但以多種方式序列化物件。 例如，您可以將其序列化為 XML 屬性，而不是將類別實例的成員序列化為 XML 屬性，進而產生更有效率的檔來傳輸。

建立 XmlAttributeOverrides 物件之後，您會將它當做引數傳遞給建 XmlSerializer 構函式。 產生的 XmlSerializer 會使用 所包含的 XmlAttributeOverrides 資料來覆寫屬性，以控制物件的序列化方式。 為了達成此目的， XmlAttributeOverrides 包含已覆寫的物件型別集合，以及 XmlAttributes 與每個覆寫物件類型相關聯的物件。 物件 XmlAttributes 本身包含一組適當的屬性物件，可控制每個欄位、屬性或類別的序列化方式。

建立和使用 XmlAttributeOverrides 物件的程式如下：

1. 建立 XmlAttributes 物件。

2. 建立適合所覆寫物件的屬性物件。 例如，若要覆寫欄位或屬性，請使用新的衍生型別建立 XmlElementAttribute 。 您可以選擇性地指派新的 ElementName ，或 Namespace 覆寫基類的屬性名稱或命名空間。

3. 將屬性物件新增至適當的 XmlAttributes 屬性或集合。 例如，您會將 新增 XmlElementAttribute 至 XmlElements 物件的集合 XmlAttributes ，並指定要覆寫的成員名稱。

4. 建立 XmlAttributeOverrides 物件。

5. Add使用 方法，將 XmlAttributes 物件新增至 XmlAttributeOverrides 物件。 如果被覆寫的物件是 XmlRootAttribute 或 XmlTypeAttribute ，您只需要指定覆寫物件的類型。 但是，如果您要覆寫欄位或屬性，您也必須指定覆寫成員的名稱。

6. 建 XmlSerializer 構 時，將 傳遞 XmlAttributeOverrides 至建構函 XmlSerializer 式。

7. 使用產生的 XmlSerializer 來序列化或還原序列化衍生類別物件。

建構函式

XmlAttributeOverrides()

初始化 XmlAttributeOverrides 類別的新執行個體。

屬性

Item[Type, String]	取得與指定的 (基底類別) 型別相關的物件。 成員參數會指定已覆寫的基底類別成員。
Item[Type]	取得與指定的、基底類別、型別相關的物件

方法

Add(Type, String, XmlAttributes)	將 XmlAttributes 物件加入 XmlAttributes 物件的集合。 type 參數會指定要被覆寫的物件。 member 參數指定覆寫的成員名稱。
Add(Type, XmlAttributes)	將 XmlAttributes 物件加入 XmlAttributes 物件的集合。 type 參數會指定要由 XmlAttributes 物件覆寫的物件。
Equals(Object)	判斷指定的物件是否等於目前的物件。 (繼承來源 Object)
GetHashCode()	做為預設雜湊函式。 (繼承來源 Object)
GetType()	取得目前執行個體的 Type。 (繼承來源 Object)
MemberwiseClone()	建立目前 Object 的淺層複製。 (繼承來源 Object)
ToString()	傳回代表目前物件的字串。 (繼承來源 Object)

另請參閱

• Deserialize(Stream)
• Serialize(TextWriter, Object)
• XmlSerializer
• XmlAttributes
• XML 序列化簡介
• HOW TO：指定 XML 資料流的替代元素名稱
• 使用屬性控制 XML 序列化
• XML 序列化的範例
• XML Schema Definition Tool (Xsd.exe)