Examples of XML Serialization
XML serialization can take more than one form, from simple to complex. For example, you can serialize a class that simply consists of public fields and properties, as shown in Introducing XML Serialization. The following examples address various advanced scenarios, including how to use XML serialization to generate an XML stream that conforms to a specific XML Schema (XSD) document.
Serializing a DataSet
Besides serializing an instance of a public class, an instance of a DataSet can also be serialized, as shown in the following example.
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
[C#]
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();
}
Serializing An XmlElement and XmlNode
You can also serialize instances of an XmlElement or XmlNode class, as shown in the following example.
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
[C#]
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();
}
Serializing a Class Containing a Field Returning a Complex Object
If a property or field returns a complex object (such as an array or a class instance), the XmlSerializer converts it to an element nested within the main XML document. For example, the first class in the following code returns an instance of the second class.
Public Class PurchaseOrder
Public MyAdress As Address
End Class
Public Class Address
Public FirstName As String
End Class
[C#]
public class PurchaseOrder
{
public Address MyAddress;
}
public class Address
{
public string FirstName;
}
The serialized XML output might resemble the following.
<PurchaseOrder>
<Address>
<FirstName>George</FirstName>
</Address>
</PurchaseOrder>
Serializing an Array of Objects
You can also serialize a field that returns an array of objects, as shown in the following example.
Public Class PurchaseOrder
public ItemsOrders () As Item
End Class
Public Class Item
Public ItemID As String
Public ItemPrice As decimal
End Class
[C#]
public class PurchaseOrder
{
public Item [] ItemsOrders
}
public class Item
{
public string ItemID
public decimal ItemPrice
}
The serialized class instance might resemble the following, if two items are ordered.
<PurchaseOrder xmlns:xsi=http://www.w3.org/2001/XMLSchema-instance xmlns:xsd="http://www.w3.org/20001/XMLSchema">
<Items>
<Item>
<ItemID>aaa111</ItemID>
<ItemPrice>34.22</ItemPrice>
<Item>
<Item>
<ItemID>bbb222</ItemID>
<ItemPrice>2.89</ItemPrice>
<Item>
</Items>
</PurchaseOrder>
Serializing a Class that Implements the ICollection Interface
You can create your own collection classes by implementing the ICollection interface, and use the XmlSerializer to serialize instances of these classes. Note that when a class implements the ICollection interface, only the collection contained by the class is serialized. Any public properties or fields added to the class will not be serialized. The class must include an Add method and an Item property (C# indexer) to be serialized.
Imports System
Imports System.IO
Imports System.Collections
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
[C#]
using System;
using System.IO;
using System.Collections;
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]{
get{return (Employee) empArray[index];}
}
public void CopyTo(Array a, int index){
empArray.CopyTo(a, index);
}
public int Count{
get{return empArray.Count;}
}
public object SyncRoot{
get{return this;}
}
public bool IsSynchronized{
get{return false;}
}
public IEnumerator GetEnumerator(){
return 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;
}
}
Purchase Order Example
You can cut and paste the following example code into a text file renamed with a .cs or .vb file name extension. Use the C# or Visual Basic compiler to compile the file. Then run it using the name of the executable.
This example uses a simple scenario to demonstrate how an instance of an object is created and serialized into a file stream using the Serialize method. The XML stream is saved to a file, and the same file is then read back and reconstructed into a copy of the original object using the Deserialize method.
In this example, a class named PurchaseOrder is serialized and then deserialized. A second class named Address is also included because the public field named ShipTo must be set to an Address. Similarly, an OrderedItem class is included because an array of OrderedItem objects must be set to the OrderedItems field. Finally, a class named Test contains the code that serializes and deserializes the classes.
The CreatePO method creates the PurchaseOrder, Address, and OrderedItem class objects, and sets the public field values. The method also constructs an instance of the XmlSerializer class that is used to serialize and deserialize the PurchaseOrder. Note that the code passes the type of the class that will be serialized to the constructor. The code also creates a FileStream that is used to write the XML stream to an XML document.
The ReadPo method is a little simpler. It just creates objects to deserialize and reads out their values. As with the CreatePo method, you must first construct an XmlSerializer, passing the type of the class to be deserialized to the constructor. Also, a FileStream is required to read the XML document. To deserialize the objects, call the Deserialize method with the FileStream as an argument. The deserialized object must be cast to an object variable of type PurchaseOrder. The code then reads the values of the deserialized PurchaseOrder. Note that you can also read the PO.xml file that is created to see the actual XML output.
Imports System
Imports System.Xml
Imports System.Xml.Serialization
Imports System.IO
Imports Microsoft.VisualBasic
' The XmlRootAttribute allows you to set an alternate name
' (PurchaseOrder)of the XML element, the element 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.
<XmlRootAttribute("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 the default of "OrderedItems" to "Items".
<XmlArrayAttribute("Items")> _
Public OrderedItems() As OrderedItem
Public SubTotal As Decimal
Public ShipCost As Decimal
Public TotalCost As Decimal
End Class
Public Class Address
' The XmlAttribute instructs the XmlSerializer to serialize the Name
' field as an XML attribute instead of an XML element (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.
<XmlElementAttribute(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;
' specify 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
[C#]
using System;
using System.Xml;
using System.Xml.Serialization;
using System.IO;
// The XmlRootAttribute 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.
[XmlRootAttribute("PurchaseOrder", Namespace="http://www.cpandl.com",
IsNullable = false)]
public class PurchaseOrder
{
public Address ShipTo;
public string OrderDate;
// The XmlArrayAttribute changes the XML element name
// from the default of "OrderedItems" to "Items".
[XmlArrayAttribute("Items")]
public OrderedItem[] OrderedItems;
public decimal SubTotal;
public decimal ShipCost;
public decimal TotalCost;
}
public class Address
{
// The XmlAttribute instructs the XmlSerializer to serialize the Name
// field as an XML attribute instead of an XML element (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.
[XmlElementAttribute(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 + "'");
}
}
The XML output might resemble the following.
<?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>
See Also
Introducing XML Serialization | Controlling XML Serialization Using Attributes | Attributes That Control XML Serialization | XmlSerializer Class