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Examples of XML Serialization

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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 code 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, you can also serialize an instance of a DataSet, as shown in the following code 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

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 code 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

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 that contains 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 example returns an instance of the second class:

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;
}

The serialized XML output might look like this:

<PurchaseOrder>
    <MyAddress>
        <FirstName>George</FirstName>
    </MyAddress>
</PurchaseOrder>

Serializing an array of objects

You can also serialize a field that returns an array of objects, as shown in the following code example:

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;
}

If two items are ordered, the serialized class instance might look like the following code:

<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>

Serializing a class that implements the ICollection interface

You can create your own collection classes by implementing the ICollection interface and using the XmlSerializer to serialize instances of these classes.

Note

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 won't be serialized. To be serialized, the class must include an Add method and an Item property (C# indexer).

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;
    }
}

Purchase Order example

You can cut and paste the following example code into a text file and rename it 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. The same file is then read 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's used to serialize and deserialize the PurchaseOrder.

Note

The code passes the type of class that will be serialized to the constructor. The code also creates a FileStream that's 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 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

You can read the PO.xml file that's created to see the actual XML output.

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 + "'");
    }
}

The XML output might look like this:

<?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