Esempi di serializzazione XML
La serializzazione XML può avere più di una forma, da semplice a complessa. È ad esempio possibile serializzare una classe costituita semplicemente da proprietà e campi pubblici, come illustrato in Introduzione alla serializzazione XML. Negli esempi di codice riportati di seguito vengono esaminati vari scenari avanzati, nonché come utilizzare la serializzazione XML per generare un flusso XML conforme a un documento XML Schema (XSD) specifico.
Serializzazione di un Dataset
Oltre alla possibilità di serializzare un'istanza di una classe pubblica, è anche possibile serializzare un'istanza di DataSet, come mostra l'esempio di codice riportato di seguito:
Private Sub SerializeDataSet(filename As String)
Dim ser As XmlSerializer = new XmlSerializer(GetType(DataSet))
' Creates a DataSet; adds a table, column, and ten rows.
Dim ds As DataSet = new DataSet("myDataSet")
Dim t As DataTable = new DataTable("table1")
Dim c As DataColumn = new DataColumn("thing")
t.Columns.Add(c)
ds.Tables.Add(t)
Dim r As DataRow
Dim i As Integer
for i = 0 to 10
r = t.NewRow()
r(0) = "Thing " & i
t.Rows.Add(r)
Next
Dim writer As TextWriter = new StreamWriter(filename)
ser.Serialize(writer, ds)
writer.Close()
End Sub
private void SerializeDataSet(string filename)
{
XmlSerializer ser = new XmlSerializer(typeof(DataSet));
// Creates a DataSet; adds a table, column, and ten rows.
DataSet ds = new DataSet("myDataSet");
DataTable t = new DataTable("table1");
DataColumn c = new DataColumn("thing");
t.Columns.Add(c);
ds.Tables.Add(t);
DataRow r;
for (int i = 0; i < 10; i++) {
r = t.NewRow();
r[0] = "Thing " + i;
t.Rows.Add(r);
}
TextWriter writer = new StreamWriter(filename);
ser.Serialize(writer, ds);
writer.Close();
}
Serializzazione di XmlElement e XmlNode
È anche possibile serializzare le istanze di una classe XmlElement o XmlNode, come illustrato nell'esempio di codice seguente:
private Sub SerializeElement(filename As String)
Dim ser As XmlSerializer = new XmlSerializer(GetType(XmlElement))
Dim myElement As XmlElement = _
new XmlDocument().CreateElement("MyElement", "ns")
myElement.InnerText = "Hello World"
Dim writer As TextWriter = new StreamWriter(filename)
ser.Serialize(writer, myElement)
writer.Close()
End Sub
Private Sub SerializeNode(filename As String)
Dim ser As XmlSerializer = _
new XmlSerializer(GetType(XmlNode))
Dim myNode As XmlNode = new XmlDocument(). _
CreateNode(XmlNodeType.Element, "MyNode", "ns")
myNode.InnerText = "Hello Node"
Dim writer As TextWriter = new StreamWriter(filename)
ser.Serialize(writer, myNode)
writer.Close()
End Sub
private void SerializeElement(string filename)
{
XmlSerializer ser = new XmlSerializer(typeof(XmlElement));
XmlElement myElement = new XmlDocument().CreateElement("MyElement", "ns");
myElement.InnerText = "Hello World";
TextWriter writer = new StreamWriter(filename);
ser.Serialize(writer, myElement);
writer.Close();
}
private void SerializeNode(string filename)
{
XmlSerializer ser = new XmlSerializer(typeof(XmlNode));
XmlNode myNode = new XmlDocument().
CreateNode(XmlNodeType.Element, "MyNode", "ns");
myNode.InnerText = "Hello Node";
TextWriter writer = new StreamWriter(filename);
ser.Serialize(writer, myNode);
writer.Close();
}
Serializzazione di una classe contenente un campo che restituisce un oggetto complesso
Se una proprietà o un campo restituisce un oggetto complesso (come una matrice o l'istanza di una classe), XmlSerializer lo converte in un elemento annidato nel documento XML principale. Ad esempio, la prima classe nell'esempio di codice riportato di seguito restituisce un'istanza della seconda classe:
Public Class PurchaseOrder
Public MyAddress As Address
End Class
Public Class Address
Public FirstName As String
End Class
public class PurchaseOrder
{
public Address MyAddress;
}
public record Address
{
public string FirstName;
}
L'output XML serializzato potrebbe essere simile al seguente:
<PurchaseOrder>
<MyAddress>
<FirstName>George</FirstName>
</MyAddress>
</PurchaseOrder>
Serializzazione di una matrice di oggetti
È inoltre possibile serializzare un campo che restituisce una matrice di oggetti, come mostra l'esempio di codice riportato di seguito:
Public Class PurchaseOrder
public ItemsOrders () As Item
End Class
Public Class Item
Public ItemID As String
Public ItemPrice As decimal
End Class
public class PurchaseOrder
{
public Item [] ItemsOrders;
}
public class Item
{
public string ItemID;
public decimal ItemPrice;
}
Se vengono ordinati due elementi, l'istanza della classe serializzata potrebbe essere simile al codice seguente:
<PurchaseOrder xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<ItemsOrders>
<Item>
<ItemID>aaa111</ItemID>
<ItemPrice>34.22</ItemPrice>
</Item>
<Item>
<ItemID>bbb222</ItemID>
<ItemPrice>2.89</ItemPrice>
</Item>
</ItemsOrders>
</PurchaseOrder>
Serializzazione di una classe che implementa l'interfaccia ICollection
È possibile creare classi di raccolte mediante l'implementazione dell'interfaccia ICollection e utilizzare XmlSerializer per serializzare istanze di tali classi.
Nota
Quando una classe implementa l'interfaccia ICollection, viene serializzata solo la raccolta contenuta dalla classe. Le proprietà o i campi pubblici aggiunti alla classe non verranno serializzati. Per essere serializzata, la classe deve includere un metodo Add e una proprietà Item (indicizzatore C#).
Imports System.Collections
Imports System.IO
Imports System.Xml.Serialization
Public Class Test
Shared Sub Main()
Dim t As Test= new Test()
t.SerializeCollection("coll.xml")
End Sub
Private Sub SerializeCollection(filename As String)
Dim Emps As Employees = new Employees()
' Note that only the collection is serialized -- not the
' CollectionName or any other public property of the class.
Emps.CollectionName = "Employees"
Dim John100 As Employee = new Employee("John", "100xxx")
Emps.Add(John100)
Dim x As XmlSerializer = new XmlSerializer(GetType(Employees))
Dim writer As TextWriter = new StreamWriter(filename)
x.Serialize(writer, Emps)
writer.Close()
End Sub
End Class
Public Class Employees
Implements ICollection
Public CollectionName As String
Private empArray As ArrayList = new ArrayList()
Public ReadOnly Default Overloads _
Property Item(index As Integer) As Employee
get
return CType (empArray(index), Employee)
End Get
End Property
Public Sub CopyTo(a As Array, index As Integer) _
Implements ICollection.CopyTo
empArray.CopyTo(a, index)
End Sub
Public ReadOnly Property Count () As integer Implements _
ICollection.Count
get
Count = empArray.Count
End Get
End Property
Public ReadOnly Property SyncRoot ()As Object _
Implements ICollection.SyncRoot
get
return me
End Get
End Property
Public ReadOnly Property IsSynchronized () As Boolean _
Implements ICollection.IsSynchronized
get
return false
End Get
End Property
Public Function GetEnumerator() As IEnumerator _
Implements IEnumerable.GetEnumerator
return empArray.GetEnumerator()
End Function
Public Function Add(newEmployee As Employee) As Integer
empArray.Add(newEmployee)
return empArray.Count
End Function
End Class
Public Class Employee
Public EmpName As String
Public EmpID As String
Public Sub New ()
End Sub
Public Sub New (newName As String , newID As String )
EmpName = newName
EmpID = newID
End Sub
End Class
using System;
using System.Collections;
using System.IO;
using System.Xml.Serialization;
public class Test
{
static void Main()
{
Test t = new Test();
t.SerializeCollection("coll.xml");
}
private void SerializeCollection(string filename)
{
Employees Emps = new Employees();
// Note that only the collection is serialized -- not the
// CollectionName or any other public property of the class.
Emps.CollectionName = "Employees";
Employee John100 = new Employee("John", "100xxx");
Emps.Add(John100);
XmlSerializer x = new XmlSerializer(typeof(Employees));
TextWriter writer = new StreamWriter(filename);
x.Serialize(writer, Emps);
}
}
public class Employees : ICollection
{
public string CollectionName;
private ArrayList empArray = new ArrayList();
public Employee this[int index] => (Employee) empArray[index];
public void CopyTo(Array a, int index)
{
empArray.CopyTo(a, index);
}
public int Count => empArray.Count;
public object SyncRoot => this;
public bool IsSynchronized => false;
public IEnumerator GetEnumerator() => empArray.GetEnumerator();
public void Add(Employee newEmployee)
{
empArray.Add(newEmployee);
}
}
public class Employee
{
public string EmpName;
public string EmpID;
public Employee() {}
public Employee(string empName, string empID)
{
EmpName = empName;
EmpID = empID;
}
}
Esempio di ordine di acquisto
È possibile tagliare e incollare il codice di esempio riportato di seguito in un file di testo e rinominarlo con un'estensione del nome file .cs o .vb. Utilizzare il compilatore C# o Visual Basic per compilare il file. Quindi eseguirlo utilizzando il nome del file eseguibile.
In questo esempio viene utilizzato un semplice scenario per dimostrare come viene creata e serializzata un'istanza di un oggetto in un flusso di file tramite il metodo Serialize. Il flusso XML viene salvato in un file. Lo stesso file viene quindi letto e ricostruito in una copia dell'oggetto originale usando il metodo Deserialize.
In questo esempio, viene serializzata e successivamente deserializzata una classe denominata PurchaseOrder
. Viene inoltre inclusa una seconda classe denominata Address
, poiché il campo pubblico denominato ShipTo
deve essere impostato su un Address
. Analogamente, viene inclusa una classe OrderedItem
, poiché è necessario impostare una matrice di oggetti OrderedItem
nel campo OrderedItems
. Infine, una classe denominata Test
contiene il codice che serializza e deserializza le classi.
Il metodo CreatePO
crea gli oggetti di classe PurchaseOrder
, Address
e OrderedItem
, e imposta i valori del campo pubblico. Il metodo costruisce inoltre un'istanza della classe XmlSerializer utilizzata per serializzare e deserializzare PurchaseOrder
.
Nota
Notare che il codice passa al costruttore il tipo della classe che sarà serializzato. Il codice crea anche un FileStream
utilizzato per scrivere il flusso XML in un documento XML.
Il metodo ReadPo
è un po' più semplice. Tale metodo crea semplicemente gli oggetti da deserializzare e ne legge i valori. Come per il metodo CreatePo
, è prima necessario costruire un oggetto XmlSerializer, passando il tipo di classe da deserializzare al costruttore. Inoltre, per leggere il documento XML è necessaria una classe FileStream. Per deserializzare gli oggetti, chiamare il metodo Deserialize con la classe FileStream come argomento. È necessario eseguire il cast dell'oggetto deserializzato su una variabile oggetto di tipo PurchaseOrder
. Il codice legge quindi i valori della classe PurchaseOrder
deserializzata.
Nota
È possibile leggere il file PO.xml creato per visualizzare l'output XML effettivo.
Imports System.IO
Imports System.Xml
Imports System.Xml.Serialization
Imports Microsoft.VisualBasic
' The XmlRoot attribute allows you to set an alternate name
' (PurchaseOrder) for the XML element and its namespace. By
' default, the XmlSerializer uses the class name. The attribute
' also allows you to set the XML namespace for the element. Lastly,
' the attribute sets the IsNullable property, which specifies whether
' the xsi:null attribute appears if the class instance is set to
' a null reference.
<XmlRoot("PurchaseOrder", _
Namespace := "http://www.cpandl.com", IsNullable := False)> _
Public Class PurchaseOrder
Public ShipTo As Address
Public OrderDate As String
' The XmlArrayAttribute changes the XML element name
' from the default of "OrderedItems" to "Items".
<XmlArray("Items")> _
Public OrderedItems() As OrderedItem
Public SubTotal As Decimal
Public ShipCost As Decimal
Public TotalCost As Decimal
End Class
Public Class Address
' The XmlAttribute attribute instructs the XmlSerializer to serialize the
' Name field as an XML attribute instead of an XML element (XML element is
' the default behavior).
<XmlAttribute()> _
Public Name As String
Public Line1 As String
' Setting the IsNullable property to false instructs the
' XmlSerializer that the XML attribute will not appear if
' the City field is set to a null reference.
<XmlElement(IsNullable := False)> _
Public City As String
Public State As String
Public Zip As String
End Class
Public Class OrderedItem
Public ItemName As String
Public Description As String
Public UnitPrice As Decimal
Public Quantity As Integer
Public LineTotal As Decimal
' Calculate is a custom method that calculates the price per item
' and stores the value in a field.
Public Sub Calculate()
LineTotal = UnitPrice * Quantity
End Sub
End Class
Public Class Test
Public Shared Sub Main()
' Read and write purchase orders.
Dim t As New Test()
t.CreatePO("po.xml")
t.ReadPO("po.xml")
End Sub
Private Sub CreatePO(filename As String)
' Creates an instance of the XmlSerializer class;
' specifies the type of object to serialize.
Dim serializer As New XmlSerializer(GetType(PurchaseOrder))
Dim writer As New StreamWriter(filename)
Dim po As New PurchaseOrder()
' Creates an address to ship and bill to.
Dim billAddress As New Address()
billAddress.Name = "Teresa Atkinson"
billAddress.Line1 = "1 Main St."
billAddress.City = "AnyTown"
billAddress.State = "WA"
billAddress.Zip = "00000"
' Set ShipTo and BillTo to the same addressee.
po.ShipTo = billAddress
po.OrderDate = System.DateTime.Now.ToLongDateString()
' Creates an OrderedItem.
Dim i1 As New OrderedItem()
i1.ItemName = "Widget S"
i1.Description = "Small widget"
i1.UnitPrice = CDec(5.23)
i1.Quantity = 3
i1.Calculate()
' Inserts the item into the array.
Dim items(0) As OrderedItem
items(0) = i1
po.OrderedItems = items
' Calculates the total cost.
Dim subTotal As New Decimal()
Dim oi As OrderedItem
For Each oi In items
subTotal += oi.LineTotal
Next oi
po.SubTotal = subTotal
po.ShipCost = CDec(12.51)
po.TotalCost = po.SubTotal + po.ShipCost
' Serializes the purchase order, and close the TextWriter.
serializer.Serialize(writer, po)
writer.Close()
End Sub
Protected Sub ReadPO(filename As String)
' Creates an instance of the XmlSerializer class;
' specifies the type of object to be deserialized.
Dim serializer As New XmlSerializer(GetType(PurchaseOrder))
' If the XML document has been altered with unknown
' nodes or attributes, handles them with the
' UnknownNode and UnknownAttribute events.
AddHandler serializer.UnknownNode, AddressOf serializer_UnknownNode
AddHandler serializer.UnknownAttribute, AddressOf _
serializer_UnknownAttribute
' A FileStream is needed to read the XML document.
Dim fs As New FileStream(filename, FileMode.Open)
' Declare an object variable of the type to be deserialized.
Dim po As PurchaseOrder
' Uses the Deserialize method to restore the object's state
' with data from the XML document.
po = CType(serializer.Deserialize(fs), PurchaseOrder)
' Reads the order date.
Console.WriteLine(("OrderDate: " & po.OrderDate))
' Reads the shipping address.
Dim shipTo As Address = po.ShipTo
ReadAddress(shipTo, "Ship To:")
' Reads the list of ordered items.
Dim items As OrderedItem() = po.OrderedItems
Console.WriteLine("Items to be shipped:")
Dim oi As OrderedItem
For Each oi In items
Console.WriteLine((ControlChars.Tab & oi.ItemName & _
ControlChars.Tab & _
oi.Description & ControlChars.Tab & oi.UnitPrice & _
ControlChars.Tab & _
oi.Quantity & ControlChars.Tab & oi.LineTotal))
Next oi
' Reads the subtotal, shipping cost, and total cost.
Console.WriteLine((ControlChars.Cr & New String _
(ControlChars.Tab, 5) & _
" Subtotal" & ControlChars.Tab & po.SubTotal & ControlChars.Cr & _
New String(ControlChars.Tab, 5) & " Shipping" & ControlChars.Tab & _
po.ShipCost & ControlChars.Cr & New String(ControlChars.Tab, 5) & _
" Total" & New String(ControlChars.Tab, 2) & po.TotalCost))
End Sub
Protected Sub ReadAddress(a As Address, label As String)
' Reads the fields of the Address.
Console.WriteLine(label)
Console.Write((ControlChars.Tab & a.Name & ControlChars.Cr & _
ControlChars.Tab & a.Line1 & ControlChars.Cr & ControlChars.Tab & _
a.City & ControlChars.Tab & a.State & ControlChars.Cr & _
ControlChars.Tab & a.Zip & ControlChars.Cr))
End Sub
Protected Sub serializer_UnknownNode(sender As Object, e As _
XmlNodeEventArgs)
Console.WriteLine(("Unknown Node:" & e.Name & _
ControlChars.Tab & e.Text))
End Sub
Protected Sub serializer_UnknownAttribute(sender As Object, _
e As XmlAttributeEventArgs)
Dim attr As System.Xml.XmlAttribute = e.Attr
Console.WriteLine(("Unknown attribute " & attr.Name & "='" & _
attr.Value & "'"))
End Sub 'serializer_UnknownAttribute
End Class 'Test
using System;
using System.IO;
using System.Xml;
using System.Xml.Serialization;
// The XmlRoot attribute allows you to set an alternate name
// (PurchaseOrder) for the XML element and its namespace. By
// default, the XmlSerializer uses the class name. The attribute
// also allows you to set the XML namespace for the element. Lastly,
// the attribute sets the IsNullable property, which specifies whether
// the xsi:null attribute appears if the class instance is set to
// a null reference.
[XmlRoot("PurchaseOrder", Namespace="http://www.cpandl.com",
IsNullable = false)]
public class PurchaseOrder
{
public Address ShipTo;
public string OrderDate;
// The XmlArray attribute changes the XML element name
// from the default of "OrderedItems" to "Items".
[XmlArray("Items")]
public OrderedItem[] OrderedItems;
public decimal SubTotal;
public decimal ShipCost;
public decimal TotalCost;
}
public class Address
{
// The XmlAttribute attribute instructs the XmlSerializer to serialize the
// Name field as an XML attribute instead of an XML element (XML element is
// the default behavior).
[XmlAttribute]
public string Name;
public string Line1;
// Setting the IsNullable property to false instructs the
// XmlSerializer that the XML attribute will not appear if
// the City field is set to a null reference.
[XmlElement(IsNullable = false)]
public string City;
public string State;
public string Zip;
}
public class OrderedItem
{
public string ItemName;
public string Description;
public decimal UnitPrice;
public int Quantity;
public decimal LineTotal;
// Calculate is a custom method that calculates the price per item
// and stores the value in a field.
public void Calculate()
{
LineTotal = UnitPrice * Quantity;
}
}
public class Test
{
public static void Main()
{
// Read and write purchase orders.
Test t = new Test();
t.CreatePO("po.xml");
t.ReadPO("po.xml");
}
private void CreatePO(string filename)
{
// Creates an instance of the XmlSerializer class;
// specifies the type of object to serialize.
XmlSerializer serializer = new XmlSerializer(typeof(PurchaseOrder));
TextWriter writer = new StreamWriter(filename);
PurchaseOrder po =new PurchaseOrder();
// Creates an address to ship and bill to.
Address billAddress = new Address();
billAddress.Name = "Teresa Atkinson";
billAddress.Line1 = "1 Main St.";
billAddress.City = "AnyTown";
billAddress.State = "WA";
billAddress.Zip = "00000";
// Sets ShipTo and BillTo to the same addressee.
po.ShipTo = billAddress;
po.OrderDate = System.DateTime.Now.ToLongDateString();
// Creates an OrderedItem.
OrderedItem i1 = new OrderedItem();
i1.ItemName = "Widget S";
i1.Description = "Small widget";
i1.UnitPrice = (decimal) 5.23;
i1.Quantity = 3;
i1.Calculate();
// Inserts the item into the array.
OrderedItem [] items = {i1};
po.OrderedItems = items;
// Calculate the total cost.
decimal subTotal = new decimal();
foreach(OrderedItem oi in items)
{
subTotal += oi.LineTotal;
}
po.SubTotal = subTotal;
po.ShipCost = (decimal) 12.51;
po.TotalCost = po.SubTotal + po.ShipCost;
// Serializes the purchase order, and closes the TextWriter.
serializer.Serialize(writer, po);
writer.Close();
}
protected void ReadPO(string filename)
{
// Creates an instance of the XmlSerializer class;
// specifies the type of object to be deserialized.
XmlSerializer serializer = new XmlSerializer(typeof(PurchaseOrder));
// If the XML document has been altered with unknown
// nodes or attributes, handles them with the
// UnknownNode and UnknownAttribute events.
serializer.UnknownNode+= new
XmlNodeEventHandler(serializer_UnknownNode);
serializer.UnknownAttribute+= new
XmlAttributeEventHandler(serializer_UnknownAttribute);
// A FileStream is needed to read the XML document.
FileStream fs = new FileStream(filename, FileMode.Open);
// Declares an object variable of the type to be deserialized.
PurchaseOrder po;
// Uses the Deserialize method to restore the object's state
// with data from the XML document. */
po = (PurchaseOrder) serializer.Deserialize(fs);
// Reads the order date.
Console.WriteLine ("OrderDate: " + po.OrderDate);
// Reads the shipping address.
Address shipTo = po.ShipTo;
ReadAddress(shipTo, "Ship To:");
// Reads the list of ordered items.
OrderedItem [] items = po.OrderedItems;
Console.WriteLine("Items to be shipped:");
foreach(OrderedItem oi in items)
{
Console.WriteLine("\t"+
oi.ItemName + "\t" +
oi.Description + "\t" +
oi.UnitPrice + "\t" +
oi.Quantity + "\t" +
oi.LineTotal);
}
// Reads the subtotal, shipping cost, and total cost.
Console.WriteLine(
"\n\t\t\t\t\t Subtotal\t" + po.SubTotal +
"\n\t\t\t\t\t Shipping\t" + po.ShipCost +
"\n\t\t\t\t\t Total\t\t" + po.TotalCost
);
}
protected void ReadAddress(Address a, string label)
{
// Reads the fields of the Address.
Console.WriteLine(label);
Console.Write("\t"+
a.Name +"\n\t" +
a.Line1 +"\n\t" +
a.City +"\t" +
a.State +"\n\t" +
a.Zip +"\n");
}
protected void serializer_UnknownNode
(object sender, XmlNodeEventArgs e)
{
Console.WriteLine("Unknown Node:" + e.Name + "\t" + e.Text);
}
protected void serializer_UnknownAttribute
(object sender, XmlAttributeEventArgs e)
{
System.Xml.XmlAttribute attr = e.Attr;
Console.WriteLine("Unknown attribute " +
attr.Name + "='" + attr.Value + "'");
}
}
L'output XML potrebbe essere simile al seguente:
<?xml version="1.0" encoding="utf-8"?>
<PurchaseOrder xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://www.cpandl.com">
<ShipTo Name="Teresa Atkinson">
<Line1>1 Main St.</Line1>
<City>AnyTown</City>
<State>WA</State>
<Zip>00000</Zip>
</ShipTo>
<OrderDate>Wednesday, June 27, 2001</OrderDate>
<Items>
<OrderedItem>
<ItemName>Widget S</ItemName>
<Description>Small widget</Description>
<UnitPrice>5.23</UnitPrice>
<Quantity>3</Quantity>
<LineTotal>15.69</LineTotal>
</OrderedItem>
</Items>
<SubTotal>15.69</SubTotal>
<ShipCost>12.51</ShipCost>
<TotalCost>28.2</TotalCost>
</PurchaseOrder>