This would produce:

The Inner XML Code of a Node

If you want only the markup(s) of the child(ren) excluding the parent, access its XmlNode.InnerXml property which is declared as follows:

public virtual string InnerXml { get; set; }

Here is an example:

private void btnDocumentClick(object sender, EventArgs e)
{
    XmlDocument docVideo = new XmlDocument();
    string Filename = "videos.xml";

    if (File.Exists(Filename))
    {
        docVideo.Load(Filename);
        XmlElement elm = docVideo.DocumentElement;
        rchDocument.Text = elm.InnerXml;
    }
    else
        MessageBox.Show("The file " + Filename + " was not found",
                        "Video Collection",
                        MessageBoxButtons.OK, MessageBoxIcon.Information);
}

This would produce:

The  Child Nodes of  a Node

Introduction

As mentioned already, one node can be nested inside of another. A nested node is called a child of the nesting node. This also implies that a node can have as many children as necessary, making them child nodes of the parent node. Once again, consider our videos.xml example:

<?xml version="1.0" encoding="utf-8"?>
<videos>
    <video>
	<title>The Distinguished Gentleman</title>
	<director>Jonathan Lynn</director>
	<length>112 Minutes</length>
	<format>DVD</format>
	<rating>R</rating>
    </video>
    <video>
	<title>Her Alibi</title>
	<director>Bruce Beresford</director>
	<length>94 Mins</length>
	<format>DVD</format>
	<rating>PG-13</rating>
    </video>
    <video>
	<title>Chalte Chalte</title>
	<director>Aziz Mirza</director>
	<length>145 Mins</length>
	<format>DVD</format>
	<rating>N/R</rating>
    </video>
</videos>

The title and the director nodes are children of the video node. The video node is the parent of both the title and the director nodes.

A Collection of XML Nodes

As you may know already, an XML document usually contains many nodes. To consider a collection of nodes, the .NET Framework provides a class named XmlNodeList. It starts as follows:

public abstract class XmlNodeList : IEnumerable, 
				    IDisposable

We will review the characteristics of this class in later sections.

Linking the Nodes

To manage the relationships among the nodes of an XML document, the .NET Framework provides a class named XmlLinkedNode:

public abstract class XmlLinkedNode : XmlNode

As a result, many classes derive from XmlLinkedNode. That's the case for the  XmlElement class:

public class XmlElement : XmlLinkedNode

A Collection of Child Nodes

To support the child nodes of a particular node, the XmlNode class is equipped with a property named ChildNodes. That property is of type XmlNodeList. The property is declared as follows:

public virtual XmlNodeList ChildNodes { get; }

When this property is used, it produces an XmlNodeList list, which is a collection of all nodes that share the same parent. Each item in the collection is of type XmlNode. To give you the number of nodes on an XmlNodeList collection, the class is equipped with a property named Count. Here is an example of using it:

private void btnDocumentClick(object sender, EventArgs e)
{
    XmlDocument docVideo = new XmlDocument();
    string Filename = "videos.xml";

    if (File.Exists(Filename))
    {
        docVideo.Load(Filename);
        XmlElement elm = docVideo.DocumentElement;
        XmlNodeList lstVideos = elm.ChildNodes;

        MessageBox.Show("The root element contains " +
                        lstVideos.Count + " nodes",
                        "Video Collection",
                        MessageBoxButtons.OK, MessageBoxIcon.Information);
    }
    else
        MessageBox.Show("The file " + Filename + " was not found",
                        "Video Collection",
                        MessageBoxButtons.OK, MessageBoxIcon.Information);
}

This would produce:

You can also use the Count property in a for loop to visit the members of the collection.

Practical Learning: Introducing Child Nodes

1. Return to the document code of the Employees form.
   Change the ShowEmployees method as follows:

   void ShowEmployees()
   {
       XmlDocument xdEmployees = new XmlDocument();
       string strFileName = "../../Employees.xml";
   
       if (File.Exists(strFileName))
       {
           xdEmployees.Load(strFileName);
           XmlElement xeEmployee = xdEmployees.DocumentElement;
           XmlNodeList xnlEmployees = xeEmployee.ChildNodes;
       }
   }

2. On the Standard toolbar, click the Save All button

Accessing a Node in a Collection

The children of a node, that is, the members of a ChildNodes property, or the members of an XmlNodeList collection, can be located each by an index. The first node has an index of 0, the second has an index of 1, an so on. To give you access to a node of the collection, the XmlNodeList class is equipped with an indexed property and a method named Item. Both produce the same result. For example, if a node has three children, to access the third, you can apply an index of 2 to its indexed property. Here is an example:

private void btnDocumentClick(object sender, EventArgs e)
{
    XmlDocument docVideo = new XmlDocument();
    string Filename = "videos.xml";

    if (File.Exists(Filename))
    {
        docVideo.Load(Filename);
        XmlElement elm = docVideo.DocumentElement;
        XmlNodeList lstVideos = elm.ChildNodes;

        MessageBox.Show(lstVideos[2].InnerText,
                        "Video Collection",
                        MessageBoxButtons.OK, MessageBoxIcon.Information);
    }
    else
        MessageBox.Show("The file " + Filename + " was not found",
                        "Video Collection",
                        MessageBoxButtons.OK, MessageBoxIcon.Information);
}

You can also use the Item() method to get the same result. Using a for loop, you can access each node and display the values of its children as follows:

private void btnDocumentClick(object sender, EventArgs e)
{
    XmlDocument docVideo = new XmlDocument();
    string Filename = "videos.xml";

    if (File.Exists(Filename))
    {
        docVideo.Load(Filename);
        XmlElement elm = docVideo.DocumentElement;
        XmlNodeList lstVideos = elm.ChildNodes;

        for (int i = 0; i < lstVideos.Count; i++)
            MessageBox.Show(lstVideos[i].InnerText,
                        "Video Collection",
                        MessageBoxButtons.OK, MessageBoxIcon.Information);
    }
    else
        MessageBox.Show("The file " + Filename + " was not found",
                        "Video Collection",
                        MessageBoxButtons.OK, MessageBoxIcon.Information);
}

Instead of using the indexed property, the XmlNodeList class implements the IEnumerable interface. This allows you to use a foreach loop to visit each node of the collection. Here is an example:

private void btnDocumentClick(object sender, EventArgs e)
{
    XmlDocument docVideo = new XmlDocument();
    string Filename = "videos.xml";

    if (File.Exists(Filename))
    {
        docVideo.Load(Filename);
        XmlElement elm = docVideo.DocumentElement;
        XmlNodeList lstVideos = elm.ChildNodes;

        foreach (XmlNode node in lstVideos)
            MessageBox.Show(node.InnerText,
                        "Video Collection",
                        MessageBoxButtons.OK, MessageBoxIcon.Information);
    }
    else
        MessageBox.Show("The file " + Filename + " was not found",
                        "Video Collection",
                        MessageBoxButtons.OK, MessageBoxIcon.Information);
}

To better manage and manipulate the nodes of a collection of nodes, you must be able to access the desired node. The XmlNode class combined with the XmlNodeList class provide various means of getting to a node and taking the appropriate actions.

The Parent of a Node

Not all nodes have children, obviously. For example, the title node of our videos.xml file does not have children. To find out whether a node has children, check its HasChildNodes Boolean property that is declared as follows:

public virtual bool HasChildNodes { get; }

If a node is a child, to get its parent, you can access its ParentNode property.

The First Child Node

The children of a nesting node are also recognized by their sequence. For our videos.xml file, the first line is called the first child of the DOM. This would be:

<?xml version="1.0" encoding="utf-8"?>

After identifying or locating a node, the first node that immediately follows it is referred to as its first child. In our videos.xml file, the first child of the first video node is the <title>The Distinguished Gentleman</title> element. The first child of the second <video> node is <title>Her Alibi</title>.

In the .NET Framework, the first child of a node can be retrieved by accessing the XmlNode.FirstChild property declared as follows:

public virtual XmlNode FirstChild { get; }

In the following example, every time the parser gets to a video node, it displays the value of it first child:

using System;
using System.Drawing;
using System.Windows.Forms;
using System.Xml;
using System.IO;

public class Exercise : System.Windows.Forms.Form
{
    Button btnDocument;
    ListBox lbxVideos;

    public Exercise()
    {
        InitializeComponent();
    }

    void InitializeComponent()
    {
        btnDocument = new Button();
        btnDocument.Text = "Document";
        btnDocument.Location = new Point(12, 12);
        btnDocument.Click += new EventHandler(btnDocumentClick);

        lbxVideos = new ListBox();
        lbxVideos.Location = new Point(12, 40);
        lbxVideos.Size = new Size(200, 60);

        Text = "Video Collection";
        StartPosition = FormStartPosition.CenterScreen;
        Controls.Add(btnDocument);
        Controls.Add(lbxVideos);
    }

    void btnDocumentClick(object sender, EventArgs e)
    {
        XmlDocument docVideo = new XmlDocument();
        string Filename = "videos.xml";

        if (File.Exists(Filename))
        {
            docVideo.Load(Filename);
            XmlElement elm = docVideo.DocumentElement;
            XmlNodeList lstVideos = elm.ChildNodes;

            foreach (XmlNode node in lstVideos)
                lbxVideos.Items.Add(node.FirstChild.InnerText);
        }
        else
            MessageBox.Show("The file " + Filename + " was not found",
                            "Video Collection",
                            MessageBoxButtons.OK, MessageBoxIcon.Information);
    }
}

public class Program
{
    static int Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        System.Windows.Forms.Application.Run(new Exercise());
        return 0;
    }
}

This would produce:

In this example, we started our parsing on the root node of the document. At times, you will need to consider only a particular node, such as the first child of a node. For example, you may want to use only the first child of the root. To get it, you can access the FirstChild property of the DocumentElement object of the DOM. Once you get that node, you can then do what you judge necessary. In the following example, only the values of the child nodes of the first child of the root are displayed:

private void btnDocumentClick(object sender, EventArgs e)
{
    XmlDocument docVideo = new XmlDocument();
    string Filename = "videos.xml";

    if (File.Exists(Filename))
    {
        docVideo.Load(Filename);
        XmlNode node = docVideo.DocumentElement.FirstChild;
        XmlNodeList lstVideos = node.ChildNodes;

        foreach (XmlNode child in node.ChildNodes)
            lbxVideos.Items.Add(child.InnerText);
    }
    else
        MessageBox.Show("The file " + Filename + " was not found",
                        "Video Collection",
                        MessageBoxButtons.OK, MessageBoxIcon.Information);
}

This would produce:

Consider the following modification of the Videos.xml file:

<?xml version="1.0" encoding="utf-8" ?>
<Videos>
    <Video>
	<Title>The Distinguished Gentleman</Title>
	<Director>Jonathan Lynn</Director>
	<CastMembers>
	    <Actor>Eddie Murphy</Actor>
	    <Actor>Lane Smith</Actor>
	    <Actor>Sheryl Lee Ralph</Actor>
	    <Actor>Joe Don Baker</Actor>
	    <Actor>Victoria Rowell</Actor>
	</CastMembers>
	<Length>112 Minutes</Length>
	<Format>DVD</Format>
	<Rating>R</Rating>
    </Video>
    <Video>
	<Title>Her Alibi</Title>
	<Director>Bruce Beresford</Director>
	<Length>94 Mins</Length>
	<Format>DVD</Format>
	<Rating>PG-13</Rating>
    </Video>
    <Video>
	<Title>Chalte Chalte</Title>
	<Director>Aziz Mirza</Director>
	<Length>145 Mins</Length>
	<Format>DVD</Format>
	<Rating>N/R</Rating>
    </Video>
</Videos>

Remember that when using a for or a foreach loops applied to an XmlNodeList collection, each node that you access is a complete XmlNode object and may have children. This means that you can further get the ChildNodes node of any node. Here is an example that primarily scans the nodes but looks for one whose name is CastMembers:

private void btnDocumentClick(object sender, EventArgs e)
{
    string Filename = "videos.xml";
    XmlDocument docVideo = new XmlDocument();

    if (File.Exists(Filename))
    {
        docVideo.Load(Filename);
        // Locate the root node and 
        // get a reference to its first child
        XmlNode node = docVideo.DocumentElement.FirstChild;
        // Create a list of the child nodes of 
        // the first node under the root
        XmlNodeList lstVideos = node.ChildNodes;

        // Visit each node
        for (int i = 0; i < lstVideos.Count; i++)
        {
            // Look for a node named CastMembers
            if (lstVideos[i].Name == "CastMembers")
            {
                // Once/if you find it,
                // 1. Access its first child
                // 2. Create a list of its child nodes
                XmlNodeList lstActors =
                    lstVideos[i].ChildNodes;
                // Display the values of the nodes
                for (int j = 0; j < lstActors.Count; j++)
                    lbxVideos.Items.Add(lstActors[j].InnerText);
            }
        }
    }
    else
       MessageBox.Show("The file " + Filename + " was not found",
                        "Video Collection",
                        MessageBoxButtons.OK, MessageBoxIcon.Information);
}

This would produce:

As we have learned that a node or a group of nodes can be nested inside of another node. When you get to a node, you may know or find out that it has children. You may then want to consider only the first child. Here is an example:

private void btnDocumentClick(object sender, EventArgs e)
{
    string Filename = "videos.xml";
    XmlDocument docVideo = new XmlDocument();

    if (File.Exists(Filename))
    {
        docVideo.Load(Filename);
        // Locate the root node and 
        // get a reference to its first child
        XmlNode node = docVideo.DocumentElement.FirstChild;
        // Create a list of the child nodes of 
        // the first node under the root
        XmlNodeList lstVideos = node.ChildNodes;

        // Visit each node
        for (int i = 0; i < lstVideos.Count; i++)
        {
            // Look for a node named CastMembers
            if (lstVideos[i].Name == "CastMembers")
            {
                // Once/if you find it,
                // 1. Access its first child
                // 2. Create a list of its child nodes
                XmlNodeList lstActors =
                    lstVideos[i].FirstChild.ChildNodes;
                // Display the value of its first child node
                for (int j = 0; j < lstActors.Count; j++)
                    lbxVideos.Items.Add(lstActors[j].InnerText);
            }
        }
    }
    else
        MessageBox.Show("The file " + Filename + " was not found",
                        "Video Collection",
                        MessageBoxButtons.OK, MessageBoxIcon.Information);
}

This would produce:

Practical Learning: Accessing the First Child Node

1. Display the Tenant Registration Editor form and click the Employee # text box
2. On the Properties window, click the Events button and double-click Leave
3. Implement the event as follows:

   using System;
   using System.Collections.Generic;
   using System.ComponentModel;
   using System.Data;
   using System.Drawing;
   using System.Linq;
   using System.Text;
   using System.Windows.Forms;
   using System.IO;
   using System.Xml;
   
   namespace LambdaSquareApartments2
   {
       public partial class TenantRegistrationEditor : Form
       {
           public TenantRegistrationEditor()
           {
               InitializeComponent();
           }
   
           private void txtEmployeeNumber_Leave(object sender, EventArgs e)
           {
               XmlDocument docEmployees = new XmlDocument();
               string strFileName = @"C:\Microsoft Visual C# Application Design\Lambda Square Apartments\Employees.xml";
   
               if (File.Exists(strFileName))
               {
                   docEmployees.Load(strFileName);
                   XmlElement xeEmployee = docEmployees.DocumentElement;
                   XmlNodeList lstEmployees = xeEmployee.ChildNodes;
   
                   foreach(XmlNode xnEmployee in lstEmployees)
                   {
                       if( xnEmployee.FirstChild.InnerText == txtEmployeeNumber.Text)
                       {
                       }
                   }
               }
           }
       }
   }

The Last Child Node

As opposed to the first child, the child node that immediately precedes the end-tag of the parent node is called the last child. To get the last child of a node, you can access its XmlNode.LastChild property that is declared as follows:

public virtual XmlNode LastChild { get; }

The Siblings of a Node

The child nodes that are nested in a parent node and share the same level are referred to as siblings. Consider the above file: Director, CastMembers, and Length are child nodes of the Video node but the Actor node is not a child of the Video node. Consequently, Director, CastMembers, and Length are siblings. Obviously, to get a sibling, you must first have a node.

To access the sibling of a node, you can use its XmlNode.NextSibling property, which is declared as follows:

public virtual XmlNode NextSibling { get; }

Consider the following XML document:

<?xml version="1.0" encoding="utf-8"?>
<Properties>
	<Property>
		<PropertyCode>724-795</PropertyCode>
		<PropertyType>Apartment</PropertyType>
		<Bedrooms>1</Bedrooms>
		<Bathrooms>1</Bathrooms>
		<MonthlyRent>925</MonthlyRent>
		<Status>Occupied</Status>
	</Property>
	<Property>
		<PropertyCode>296-283</PropertyCode>
		<PropertyType>Apartment</PropertyType>
		<Bedrooms>2</Bedrooms>
		<Bathrooms>1</Bathrooms>
		<MonthlyRent>1150.50</MonthlyRent>
		<Status>Available</Status>
	</Property>
</Properties>

Here are examples of using the NextSibling property:

private void SolasPropertyRental_Load(object sender, EventArgs e)
{
    string Filename = "Properties.xml";
    XmlDocument docProperties = new XmlDocument();

    if (File.Exists(Filename))
    {
        docProperties.Load(Filename);
        XmlElement elmProperty = docProperties.DocumentElement;
        XmlNodeList lstProperties = elmProperty.ChildNodes;

        foreach(XmlNode node in lstProperties)
        {
            ListViewItem lviProperty = new ListViewItem(node.FirstChild.InnerText); // Property code

            lviProperty.SubItems.Add(node.FirstChild.NextSibling.InnerText); // Property Type
            lviProperty.SubItems.Add(node.FirstChild.NextSibling.NextSibling.InnerText); // Bedrooms
            lviProperty.SubItems.Add(node.FirstChild.NextSibling.NextSibling.NextSibling.InnerText); // Bathrooms
            lviProperty.SubItems.Add(node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // Monthly Rent
            lviProperty.SubItems.Add(node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // Status
            lvwProperties.Items.Add(lviProperty);
        }
    }
    else
        MessageBox.Show("The " + Filename + " file was not found");
}

Practical Learning: Using the Siblings of an XML Node

1. Display the Employees form
2. Right-click its body and click View Code
3. Change the document as follows:

   using System;sing System.Collections.Generic;
   using System.ComponentModel;
   using System.Data;
   using System.Drawing;
   using System.Linq;
   using System.Text;
   using System.Windows.Forms;
   using System.IO;
   using System.Xml;
   
   namespace LambdaSquareApartments2
   {
       public partial class Employees : Form
       {
           public Employees()
           {
               InitializeComponent();
           }
   
           void ShowEmployees()
           {
               XmlDocument xdEmployees = new XmlDocument();
               string strFileName = @"C:\Microsoft Visual C# Application Design\Lambda Square Apartments\Employees.xml";
   
               if (File.Exists(strFileName))
               {
                   lvwEmployees.Items.Clear();
   
                   xdEmployees.Load(strFileName);
                   XmlElement xeEmployee = xdEmployees.DocumentElement;
                   XmlNodeList xnlEmployees = xeEmployee.ChildNodes;
   
                   foreach (XmlNode node in xnlEmployees)
                   {
                       ListViewItem lviEmployee = new ListViewItem(node.FirstChild.InnerText); // Employee Number
   
                       lviEmployee.SubItems.Add(node.FirstChild.NextSibling.InnerText); // First Name
                       lviEmployee.SubItems.Add(node.FirstChild.NextSibling.NextSibling.InnerText); // Last Name
                       lviEmployee.SubItems.Add(node.FirstChild.NextSibling.NextSibling.NextSibling.InnerText); // Title
   
                       lvwEmployees.Items.Add(lviEmployee);
                   }
               }
           }
   
           private void Employees_Load(object sender, EventArgs e)
           {
               ShowEmployees();
           }
       }
   }}

4. Display the Apartments form and double-click an unoccupied area of its body
5. Change the document as follows:

   using System;
   using System.Collections.Generic;
   using System.ComponentModel;
   using System.Data;
   using System.Drawing;
   using System.Linq;
   using System.Text;
   using System.Windows.Forms;
   using System.IO;
   using System.Xml;
   
   namespace LambdaSquareApartments2
   {
       public partial class Apartments : Form
       {
           public Apartments()
           {
               InitializeComponent();
           }
   
           void ShowProperties()
           {
               XmlDocument docApartments = new XmlDocument();
               string strFileName = @"C:\Microsoft Visual C# Application Design\Lambda Square Apartments\Apartments.xml";
   
               if (File.Exists(strFileName))
               {
                   lvwApartments.Items.Clear();
   
                   docApartments.Load(strFileName);
                   XmlElement elmApartment = docApartments.DocumentElement;
                   XmlNodeList lstApartments = elmApartment.ChildNodes;
   
                   foreach (XmlNode node in lstApartments)
                   {
                       ListViewItem lviApartment = new ListViewItem(node.FirstChild.InnerText); // Unit Code
   
                       lviApartment.SubItems.Add(node.FirstChild.NextSibling.InnerText); // Apartment Number
                       lviApartment.SubItems.Add(node.FirstChild.NextSibling.NextSibling.InnerText); // Bedrooms
                       lviApartment.SubItems.Add(node.FirstChild.NextSibling.NextSibling.NextSibling.InnerText); // Bathrooms
                       lviApartment.SubItems.Add(node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // Monthly Rate
                       lviApartment.SubItems.Add(node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // SecurityDeposit
                       lviApartment.SubItems.Add(node.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // Occupancy Status
   
                       lvwApartments.Items.Add(lviApartment);
                   }
               }
           }
   
           private void Apartments_Load(object sender, EventArgs e)
           {
               ShowProperties();
           }
       }
   }

6. Display the Tenant Registration Editor form and click the Employee # text box
7. In the Events section of the Properties window, double-click Leave
8. Implement the event as follows:

   using System;
   using System.Collections.Generic;
   using System.ComponentModel;
   using System.Data;
   using System.Drawing;
   using System.Linq;
   using System.Text;
   using System.Windows.Forms;
   using System.IO;
   using System.Xml;
   
   namespace LambdaSquareApartments2
   {
       public partial class TenantRegistrationEditor : Form
       {
           public TenantRegistrationEditor()
           {
               InitializeComponent();
           }
   
           private void txtEmployeeNumber_Leave(object sender, EventArgs e)
           {
               bool employeeFound = false;
               XmlDocument docEmployees = new XmlDocument();
               string strFileName = @"C:\Microsoft Visual C# Application Design\Lambda Square Apartments\Employees.xml";
   
               if (File.Exists(strFileName))
               {
                   docEmployees.Load(strFileName);
                   XmlElement xeEmployee = docEmployees.DocumentElement;
                   XmlNodeList lstEmployees = xeEmployee.ChildNodes;
   
                   foreach(XmlNode xnEmployee in lstEmployees)
                   {
                       if( xnEmployee.FirstChild.InnerText == txtEmployeeNumber.Text)
                       {
                           employeeFound = true;
                           txtEmployeeName.Text = xnEmployee.FirstChild.NextSibling.InnerText + "(" +
                                                  xnEmployee.FirstChild.NextSibling.NextSibling.InnerText + ")";
                       }
                   }
   
                   if (employeeFound == false)
                   {
                       MessageBox.Show("There is no employee with that number.",
                                       "Lambda Square Apartments",
                                       MessageBoxButtons.OK, MessageBoxIcon.Information);
                   }
               }
               else
                   MessageBox.Show("There is no list of employees to check.",
                                       "Lambda Square Apartments",
                                       MessageBoxButtons.OK, MessageBoxIcon.Information);
           }
       }
   }

9. Return to the Tenant Registration Editor form and click the Unit Code text box
10. In the Events section of the Properties window, double-click Leave
11. Implement the event as follows: 
    

    private void txtUnitCode_Leave(object sender, EventArgs e)
    {
        bool apartmentFound = false;
        XmlDocument xdApartments = new XmlDocument();
        string strFileName = @"C:\Microsoft Visual C# Application Design\Lambda Square Apartments\Apartments.xml";
    
        if (File.Exists(strFileName))
        {
            xdApartments.Load(strFileName);
            XmlElement xeApartment = xdApartments.DocumentElement;
            XmlNodeList xnlProperties = xeApartment.ChildNodes;
    
            foreach(XmlNode xnApartment in xnlProperties)
            {
                if (xnApartment.FirstChild.InnerText == txtUnitCode.Text)
                {
                    apartmentFound = true;
                    txtApartmentDetails.Text = "Bedroom(s):\t" + xnApartment.FirstChild.NextSibling.InnerText + Environment.NewLine +
                                               "Bathroom(s):\t" + xnApartment.FirstChild.NextSibling.NextSibling.InnerText + Environment.NewLine +
                                               "Monthly Rent:\t" + xnApartment.FirstChild.NextSibling.NextSibling.NextSibling.InnerText + "\\month\n" + Environment.NewLine +
                                               "Security Deposit:\t " + xnApartment.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                }
            }
    
            if (apartmentFound == false)
            {
                MessageBox.Show("There is no apartment with that unit code.",
                            "Lambda Square Apartments",
                            MessageBoxButtons.OK, MessageBoxIcon.Information);
                txtApartmentDetails.Text = "";
            }
        }
        else
            MessageBox.Show("There is no list of properties to check.",
                            "Lambda Square Apartments",
                            MessageBoxButtons.OK, MessageBoxIcon.Information);
    }

12. Display the Tenants Registrations form and double-click an unoccupied area of its body
13. Change the document as follows:

    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Drawing;
    using System.Linq;
    using System.Text;
    using System.Windows.Forms;
    using System.IO;
    using System.Xml;
    
    namespace LambdaSquareApartments2
    {
        public partial class TenantsRegistrations : Form
        {
            public TenantsRegistrations()
            {
                InitializeComponent();
            }
    
            void ShowRentalRegistrations()
            {
                XmlDocument xdEmployees = new XmlDocument();
                XmlDocument xdApartments = new XmlDocument();
                XmlDocument xdRegistrations = new XmlDocument();
                string strEmployeesFile = @"C:\Microsoft Visual C# Application Design\Lambda Square Apartments\Employees.xml";
                string strApartmentsFile = @"C:\Microsoft Visual C# Application Design\Lambda Square Apartments\Apartments.xml";
                string strTenantsRegistrationsFile = @"C:\Microsoft Visual C# Application Design\Lambda Square Apartments\TenantsRegistrations.xml";
    
                if (File.Exists(strTenantsRegistrationsFile))
                {
                    lvwRegistrations.Items.Clear();
    
                    xdEmployees.Load(strEmployeesFile);
                    xdApartments.Load(strApartmentsFile);
                    xdRegistrations.Load(strTenantsRegistrationsFile);
                    XmlElement xeEmployee = xdEmployees.DocumentElement,
                               xeApartment = xdApartments.DocumentElement,
                               xeRegistration = xdRegistrations.DocumentElement;
                    XmlNodeList xnlEmployees = xeEmployee.ChildNodes,
                                xnlApartments = xeApartment.ChildNodes,
                                xnlRegistrations = xeRegistration.ChildNodes;
    
                    foreach (XmlNode xnRegistration in xnlRegistrations)
                    {
                        ListViewItem lviRegistration = new ListViewItem(xnRegistration.FirstChild.InnerText); // Registration Number
    
                        lviRegistration.SubItems.Add(xnRegistration.FirstChild.NextSibling.InnerText); // Registration Date
    
                        foreach (XmlNode xnEmployee in xnlEmployees)
                        {
                            if (xnEmployee.FirstChild.InnerText == xnRegistration.FirstChild.NextSibling.NextSibling.InnerText)
                            {
                                lviRegistration.SubItems.Add(xnEmployee.FirstChild.InnerText + ": " + xnEmployee.FirstChild.NextSibling.InnerText + " " + xnEmployee.FirstChild.NextSibling.NextSibling.InnerText); // Employee Number
                                break;
                            }
                        }
                        lviRegistration.SubItems.Add(xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.InnerText); // Tenant Code
                        lviRegistration.SubItems.Add(xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // First Name
                        lviRegistration.SubItems.Add(xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // Last Name
                        lviRegistration.SubItems.Add(xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // Marital Status
                        lviRegistration.SubItems.Add(xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // Number of Children
                        lviRegistration.SubItems.Add(xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // Phone Number
                        lviRegistration.SubItems.Add(xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // Email Address
    
                        foreach (XmlNode xnApartment in xnlApartments)
                        {
                            if (xnApartment.FirstChild.InnerText == xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText)
                            {
                                lviRegistration.SubItems.Add("Apart #: " +
                                                             xnApartment.FirstChild.NextSibling.InnerText +
                                                             ", " + xnApartment.FirstChild.NextSibling.NextSibling.InnerText + " bedroom(s), " +
                                                             xnApartment.FirstChild.NextSibling.NextSibling.NextSibling.InnerText + " bathroom(s), " +
                                                             "Rent: " + xnApartment.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText + "/month, " +
                                                             "Deposit: " + xnApartment.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // Employee Number
                                break;
                            }
                        }
    
                        lviRegistration.SubItems.Add(xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // Rent Start Date
                        lvwRegistrations.Items.Add(lviRegistration);
                    }
                }
            }
    
            private void TenantsRegistrations_Load(object sender, EventArgs e)
            {
                ShowRentalRegistrations();
            }
        }
    }

14. Return to the Tenants Registrations form and double-click the New Registration button
15. Implement the event as follows:

    private void btnNewRegistration_Click(object sender, EventArgs e)
    {
        int iRegistrationNumber = 1000;
        XmlDocument xdRegistrations = new XmlDocument();
        TenantRegistrationEditor editor = new TenantRegistrationEditor();
        string strTenantsRegistrationsFile = @"C:\Microsoft Visual C# Application Design\Lambda Square Apartments\TenantsRegistrations.xml";
    
        if (File.Exists(strTenantsRegistrationsFile))
        {
            xdRegistrations.Load(strTenantsRegistrationsFile);
            XmlElement xeRegistration = xdRegistrations.DocumentElement;
            XmlNodeList xnlRegistrations = xeRegistration.ChildNodes;
    
            foreach (XmlNode xnRegistration in xnlRegistrations)
                iRegistrationNumber = int.Parse(xnRegistration.FirstChild.InnerText);
        }
    
        editor.txtRegistrationNumber.Text = (iRegistrationNumber + 1).ToString();
        editor.ShowDialog();
        ShowRentalRegistrations();
    }

16. Display the Payment Editor and click the Employee # text box
17. In the Events section of the Properties window, double-click Leave
18. Implement the event as follows:

    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Drawing;
    using System.Linq;
    using System.Text;
    using System.Windows.Forms;
    using System.IO;
    using System.Xml;
    
    namespace LambdaSquareApartments2
    {
        public partial class PaymentEditor : Form
        {
            public TenantRegistrationEditor()
            {
                InitializeComponent();
            }
    
            private void txtEmployeeNumber_Leave(object sender, EventArgs e)
            {
                bool employeeFound = false;
                XmlDocument docEmployees = new XmlDocument();
                string strFileName = @"C:\Microsoft Visual C# Application Design\Lambda Square Apartments\Employees.xml";
    
                if (File.Exists(strFileName))
                {
                    docEmployees.Load(strFileName);
                    XmlElement xeEmployee = docEmployees.DocumentElement;
                    XmlNodeList lstEmployees = xeEmployee.ChildNodes;
    
                    foreach(XmlNode xnEmployee in lstEmployees)
                    {
                        if( xnEmployee.FirstChild.InnerText == txtEmployeeNumber.Text)
                        {
                            employeeFound = true;
                            txtEmployeeName.Text = xnEmployee.FirstChild.NextSibling.InnerText + "(" +
                                                   xnEmployee.FirstChild.NextSibling.NextSibling.InnerText + ")";
                        }
                    }
    
                    if (employeeFound == false)
                    {
                        MessageBox.Show("There is no employee with that number.",
                                        "Lambda Square Apartments",
                                        MessageBoxButtons.OK, MessageBoxIcon.Information);
                    }
                }
                else
                    MessageBox.Show("There is no list of employees to check.",
                                        "Lambda Square Apartments",
                                        MessageBoxButtons.OK, MessageBoxIcon.Information);
            }
        }
    }

19. Return to the Payment Editor and click the Registration # text box
20. In the Events section of the Properties window, double-click Leave
21. Implement the event as follows:

    private void txtRegistrationNumber_Leave(object sender, EventArgs e)
    {
        string strUnitCode = "";
        bool registrationFound = false;
        XmlDocument xdApartments = new XmlDocument();
        XmlDocument xdRegistrations = new XmlDocument();
        string strFileName = @"C:\Microsoft Visual C# Application Design\Lambda Square Apartments\Apartments.xml";
        string strRegistrationsFile = @"C:\Microsoft Visual C# Application Design\Lambda Square Apartments\TenantsRegistrations.xml";
    
        if (File.Exists(strRegistrationsFile))
        {
            xdRegistrations.Load(strRegistrationsFile);
            XmlElement xeRegistration = xdRegistrations.DocumentElement;
            XmlNodeList xnlRegistrations = xeRegistration.ChildNodes;
    
            foreach(XmlNode xnRegistration in xnlRegistrations)
            {
                if (xnRegistration.FirstChild.InnerText == txtRegistrationNumber.Text)
                {
                    registrationFound = true;
                    txtDateRegistered.Text = xnRegistration.FirstChild.NextSibling.NextSibling.InnerText;
                    txtRentStartDate.Text  = xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.InnerText;
                    txtTenantInformation.Text = xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText + ": " +
                                                xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText + " " +
                                                xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText + ", " +
                                                xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText + ", " +
                                                xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText + " child(ren)";
                    strUnitCode = xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                }
            }
    
            xdApartments.Load(strFileName);
            XmlElement xeApartment = xdApartments.DocumentElement;
            XmlNodeList xnlApartments = xeApartment.ChildNodes;
    
            foreach (XmlNode xnApartment in xnlApartments)
            {
                if (xnApartment.FirstChild.InnerText == strUnitCode)
                    txtApartmentInformation.Text = "Apart #:\t\t" + xnApartment.FirstChild.NextSibling.InnerText + ", " + Environment.NewLine +
                                                   "Bedroom(s):\t" + xnApartment.FirstChild.NextSibling.NextSibling.InnerText + Environment.NewLine +
                                                   "Bathroom(s):\t" + xnApartment.FirstChild.NextSibling.NextSibling.NextSibling.InnerText + Environment.NewLine +
                                                   "Monthly Rate:\t" + xnApartment.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText + "/month" + Environment.NewLine +
                                                   "Deposit:\t" + xnApartment.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
            }
    
            if (registrationFound == false)
            {
                MessageBox.Show("There is no rental contral with that number.",
                                "Lambda Square Apartments",
                                MessageBoxButtons.OK, MessageBoxIcon.Information);
                txtDateRegistered.Text = "";
                txtRentStartDate.Text = "";
                txtTenantInformation.Text = "";
            }
        }
        else
            MessageBox.Show("There is no list of rental contracts to check.",
                            "Lambda Square Apartments",
                            MessageBoxButtons.OK, MessageBoxIcon.Information);       
    }

22. Display the Payments form and double-click an unoccupied area of its body
23. Change the document as follows:

    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Drawing;
    using System.Linq;
    using System.Text;
    using System.Windows.Forms;
    using System.IO;
    using System.Xml;
    
    namespace LambdaSquareApartments2
    {
        public partial class Payments : Form
        {
            public Payments()
            {
                InitializeComponent();
            }
    
            void ShowRentPayments()
            {
                XmlDocument xdPayments = new XmlDocument();
                XmlDocument xdEmployees = new XmlDocument();
                XmlDocument xdRegistrations = new XmlDocument();
                string strPaymentsFile = @"C:\Microsoft Visual C# Application Design\Lambda Square Apartments\Payments.xml";
                string strEmployeesFile = @"C:\Microsoft Visual C# Application Design\Lambda Square Apartments\Employees.xml";
                string strTenantsRegistrationsFile = @"C:\Microsoft Visual C# Application Design\Lambda Square Apartments\TenantsRegistrations.xml";
    
                if (File.Exists(strPaymentsFile))
                {
                    xdPayments.Load(strPaymentsFile);
                    xdEmployees.Load(strEmployeesFile);
                    xdRegistrations.Load(strTenantsRegistrationsFile);
                    XmlElement xePayment = xdPayments.DocumentElement,
                               xeEmployee = xdEmployees.DocumentElement,
                               xeRegistration = xdRegistrations.DocumentElement;
                    XmlNodeList xnlPayments = xePayment.ChildNodes,
                                xnlEmployees = xeEmployee.ChildNodes,
                                xnlRegistrations = xeRegistration.ChildNodes;
    
                    lvwPayments.Items.Clear();
    
                    foreach (XmlNode xnPayment in xnlPayments)
                    {
                        ListViewItem lviPayment = new ListViewItem(xnPayment.FirstChild.InnerText); // Receipt Number
    
                        lviPayment.SubItems.Add(DateTime.Parse(xnPayment.FirstChild.NextSibling.InnerText).ToShortDateString()); // Payment Date
    
                        foreach (XmlNode xnEmployee in xnlEmployees)
                        {
                            if (xnEmployee.FirstChild.InnerText == xnPayment.FirstChild.NextSibling.NextSibling.InnerText)
                            {
                                lviPayment.SubItems.Add(xnEmployee.FirstChild.InnerText + ": " + xnEmployee.FirstChild.NextSibling.InnerText + " " + xnEmployee.FirstChild.NextSibling.NextSibling.InnerText); // Employee Number
                                break;
                            }
                        }
    
                        foreach (XmlNode xnRegistration in xnlRegistrations)
                        {
                            if (xnRegistration.FirstChild.InnerText == xnPayment.FirstChild.NextSibling.NextSibling.NextSibling.InnerText)
                            {
                                lviPayment.SubItems.Add(xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.InnerText + ": " +
                                                        xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText + " " +
                                                        xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText + ", " +
                                                        xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText + ", " +
                                                        xnRegistration.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText + " child(ren)");
                                break;
                            }
                        }
    
                        lviPayment.SubItems.Add(xnPayment.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText);  // Payment Amount
                        lviPayment.SubItems.Add(xnPayment.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // Notes
                        lvwPayments.Items.Add(lviPayment);
                    }
                }
            }
    
            private void Payments_Load(object sender, EventArgs e)
            {
                ShowRentPayments();
            }
        }
    }

24. Return to the Payments form and double-click the New Payment button
25. Change the document as follows:

    private void btnNewPayment_Click(object sender, EventArgs e)
    {
        int iReceiptNumber = 100000;
        PaymentEditor editor = new PaymentEditor();
        XmlDocument xdPayments = new XmlDocument();
        string strPaymentsFile = @"C:\Microsoft Visual C# Application Design\Lambda Square Apartments\Payments.xml";
    
        if (File.Exists(strPaymentsFile))
        {
            xdPayments.Load(strPaymentsFile);
            XmlElement xePayment = xdPayments.DocumentElement;
            XmlNodeList xnlPayments = xePayment.ChildNodes;
    
            foreach (XmlNode xnPayment in xnlPayments)
                iReceiptNumber = int.Parse(xnPayment.FirstChild.InnerText);
        }
    
        editor.txtReceiptNumber.Text = (iReceiptNumber + 1).ToString();
        editor.ShowDialog();
    
        ShowRentPayments();
    }

26. On the Standard toolbar, click the Save All button