Assembly: System.Xml (in system.xml.dll)
Public Class XmlAttributes
Dim instance As XmlAttributes
public class XmlAttributes
public ref class XmlAttributes
public class XmlAttributes
public class XmlAttributes
La creazione di XmlAttributes fa parte del processo di override della modalità predefinita di serializzazione delle istanze della classe da parte di XmlSerializer. Ad esempio, se si desidera serializzare un oggetto creato da una DLL della quale non è disponibile il codice sorgente, utilizzando XmlAttributeOverrides, è possibile ottimizzare o controllare la serializzazione dell'oggetto.
I membri della classe XmlAttributes corrispondono direttamente a una famiglia di classi di attributi che consentono di controllare la serializzazione. Ad esempio, la proprietà XmlText deve essere impostata su XmlTextAttribute, che permette di eseguire l'override della serializzazione di un campo o di una proprietà facendo in modo che XmlSerializer serializzi il valore della proprietà come testo XML. Per un elenco completo di attributi che controllano la serializzazione, vedere XmlSerializer.
Per ulteriori dettagli sull'utilizzo dell'XmlAttributeOverrides con la classe XmlAttributes, vedere Procedura: specificare un nome di elemento alternativo per un flusso XML.
Nell'esempio riportato di seguito viene serializzata un'istanza di una classe denominata Orchestra, che contiene un unico campo denominato Instruments che restituisce una matrice di oggetti Instrument. Una seconda classe denominata Brass eredita dalla classe Instrument. Nell'esempio viene creato un oggetto XmlAttributes per eseguire l'override del campo Instrument, consentendo al campo di accettare oggetti Brass e viene aggiunto l'oggetto XmlAttributes a un'istanza della classe XmlAttributeOverrides.
Imports System Imports System.IO Imports System.Xml.Serialization Imports Microsoft.VisualBasic 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(ByVal 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 element to the collection of elements. 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.ToString()) Next i End Sub End Class
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 element to the collection of elements. 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); } } }
#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 element to the collection of elements. 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" ); }
import System.*;
import System.IO.*;
import System.Xml.Serialization.*;
public class Orchestra
{
public Instrument instruments[];
} //Orchestra
public class Instrument
{
public String name;
} //Instrument
public class Brass extends Instrument
{
public boolean isValved;
} //Brass
public class Run
{
public static void main(String[] args)
{
Run test = new Run();
test.SerializeObject("Override.xml");
test.DeserializeObject("Override.xml");
} //main
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.set_ElementName("Brass");
attr.set_Type(Brass.class.ToType());
// Add the element to the collection of elements.
attrs.get_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(Orchestra.class.ToType(), "instruments", attrs);
// Create the XmlSerializer using the XmlAttributeOverrides.
XmlSerializer s =
new XmlSerializer(Orchestra.class.ToType(), 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();
} //SerializeObject
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.set_ElementName("Brass");
attr.set_Type(Brass.class.ToType());
// Add the element to the collection of elements.
attrs.get_XmlElements().Add(attr);
attrOverrides.Add(Orchestra.class.ToType(), "instruments", attrs);
// Create the XmlSerializer using the XmlAttributeOverrides.
XmlSerializer s =
new XmlSerializer(Orchestra.class.ToType(), 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;
for (int iCtr = 0; iCtr < band.instruments.length; iCtr++) {
Instrument i = band.instruments[iCtr];
b = (Brass)i;
Console.WriteLine(b.name + "\n" + Convert.ToString(b.isValved));
}
} //DeserializeObject
} //Run
System.Xml.Serialization.XmlAttributes
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.NET Framework non supporta tutte le versioni di ciascuna piattaforma. Per un elenco delle versioni supportate, vedere Requisiti di sistema.
.NET Framework
Supportato in: 2.0 1.1 1.0.NET Compact Framework
Supportato in: 2.0Riferimenti
Membri XmlAttributesSpazio dei nomi System.Xml.Serialization
Classe XmlAttributeOverrides
XmlSerializer
Classe XmlAttributes
Altre risorse
Introduzione alla serializzazione XMLProcedura: specificare un nome di elemento alternativo per un flusso XML
Controllo della serializzazione XML mediante attributi
Esempi di serializzazione XML
Strumento di definizione di schemi XML (Xsd.exe)