Microsoft Visual C# XML: Maintenance of XML Elements

	Maintenance of XML Elements

Locating an Element

Introduction

In some cases, you may want to perform an operation on an existing and particular node. For example, you may want to change the value of a node, you may want to add a new child node to an existing node, etc. Before taking any of these actions, you must be able to locate or identify the desired element.

Locating an element consists of looking for a particular node among the nodes. To do this, you must start somewhere. Obviously, the first node you can identify is the root. Once you get the root, you can then get a collection of its children. After getting a collection of the children of the root, you can locate a node in the collection. If the node you are looking for is a child of that first collection, you can then get a collection of the child nodes of that node and proceed.

Fortunately, the System.Xml namespace provides various means of looking for a node in an XML file.

Practical Learning: Introducing XML Node Maintenance

Start Microsoft Visual Studio and create a new Windows Application named SoloMusicStore2
To create a dialog box, on the main menu, click PROJECT -> Add Windows Form...
Set the name to Category
Click Add

Design the form as follows:

Control	Text	Name	Other Properties
Label	C&ategory:
TextBox		txtCategory	Modifiers: Public
Button	&OK	btnOK	DialogResult: OK
Button	&Cancel	btnCancel	DialogResult: Cancel

Form Property

Value

FormBorderStyle

FixedDialog

Text

Category Editor

StartPosition

CenterScreen

AcceptButton

btnOK

CancelButton

btnCancel

MaximizeBox

False

MinimizeBox

False

ShowInTaskbar

False

To create a dialog box, on the main menu, click PROJECT -> Add Windows Form...
Set the name to SubCategory
Click Add

Design the form as follows:

Control	Text	Name	Other Properties
Label	&Sub-Category:
TextBox		txtItemType	Modifiers: Public
Button	&OK	btnOK	DialogResult: OK
Button	&Cancel	btnCancel	DialogResult: Cancel

Form Property

Value

FormBorderStyle

FixedDialog

Text

Type Editor

StartPosition

CenterScreen

AcceptButton

btnOK

CancelButton

btnCancel

MaximizeBox

False

MinimizeBox

False

ShowInTaskbar

False

To add a new form, on the main menu, click PROJECT -> Add Windows Form...
Set the Name to StoreItemEditor and click Add

Design the form as follows:

Solo Music: New Store Item

Control	(Name)	Text	Other Properties
Label		Item #:
Text Box	txtItemNumber		Modifiers: Public
Button	btnFind	Find	Modifiers: Public
Label		Category:
Combo Box	cbxCategories		Modifiers: Public
Button	btnNewCategory	New...
Label		Sub-Category:
Combo Box	cbxSubCategories		Modifiers: Public
Button	btnNewSubCategory	New...
Label		Item Name:
Text Box	txtItemName		Modifiers: Public
Label		Unit Price
Text Box	txtUnitPrice		Modifiers: Public
Button	btnOK	OK	DialogResult: OK
Button	btnCancel	Cancel	DialogResult: Cancel
Picture Box	pbxSelectedItem		BorderStyle: Fixed3D SizeMode: Zoom

Click an unoccupied area of the form and, in the Properties window, change the following characteristics:
AcceptButton: btnOK
CancelButton: btnCancel
FormBorderStyle: FixedDialog
MaximizeBox: False
MinimizeBox: False
ShowInTaskbar: False
StartPosition: CenterScreen
Click the Item Number text box
On the Properties window, click Events and double-click Leave

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 SoloMusicStore2
{
    public partial class StoreItemEditor : Form
    {
        public StoreItemMaintenance()
        {
            InitializeComponent();
        }

        private void txtItemNumber_Leave(object sender, EventArgs e)
	{
	    string strFileName = @"C:\Microsoft Visual C# Application Design\" + txtItemNumber.Text + ".jpg";

	    if (File.Exists(strFileName))
	        pbxSelectedItem.Image = Image.FromFile(strFileName);
	    else
        	pbxSelectedItem.Image = Image.FromFile(@"C:\Microsoft Visual C# Application Design\MusicItem.jpg");
	}
    }
}

Return to the Store Item Editor form and double-click the New Category button

Implement the event as follows:

private void btnNewCategory_Click(object sender, EventArgs e)
{
    Category editor = new Category();

    if (editor.ShowDialog() == DialogResult.OK)
    {
        if (!string.IsNullOrEmpty(editor.txtCategory.Text))
        {
            string strCategory = editor.txtCategory.Text;

            // Make sure the category is not yet in the list
            if (cbxCategories.Items.Contains(strCategory))
                MessageBox.Show(strCategory + " is already in the list.",
                                "Solo Music Store",
                                MessageBoxButtons.OK, MessageBoxIcon.Information);
            else
            {
                // Since this is a new category, add it to the combox box
                cbxCategories.Items.Add(strCategory);
                // Just in case the user wanted to use this new category
                // select it
                cbxCategories.Text = strCategory;
            }
        }
    }
}

Return to the Store Item Editor dialog box and double-click the New Sub-Category button

Implement the event as follows:

private void btnNewSubCategory_Click(object sender, EventArgs e)
{
    SubCategory editor = new SubCategory();

    if (editor.ShowDialog() == DialogResult.OK)
    {
        if (!string.IsNullOrEmpty(editor.txtSubCategory.Text))
        {
            string strSubCategory = editor.txtSubCategory.Text;

            if (cbxSubCategories.Items.Contains(strSubCategory))
                MessageBox.Show(strSubCategory + " exists already.",
                                "Solo Music Store",
                                MessageBoxButtons.OK, MessageBoxIcon.Information);
            else
            {
                cbxSubCategories.Items.Add(strSubCategory);
                cbxSubCategories.Text = strSubCategory;
            }
        }
    }
}

In the Solution Explorer, right-click Form1.cs and click Rename
Change the name to SoloMusicStore and press Enter twice

Design the form as follows:

Control

Text

Name

Other Properties

Label

Item Category

Label

Item Sub-Category

Label

Available Items

ListBox

lbxCategories

ListBox

lbxSubCategories

ListView

lvwAvailableItems

View: Details
FullRowSelect: True
GridLines: True

Columns

(Name)	Text	TextAlign	Width
colItemNumber	Item #
colItemName	Item Name		320
colUnitPrice	Unit Price	Right

PictureBox

pbxStoreItem

SizeMode: Zoom

Button

New Store Item...

btnNewStoreItem

Button

Update Store Item...

btnUpdateStoreItem

Button

Delete Store Item...

btnDeleteStoreItem

Button

btnClose

On the form, click the list view and, on the Properties window, click the Events button

Double-click ItemSelectionChanged and 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 SoloMusicStore2
{
    public partial class SoloMusicStore : Form
    {
        public SoloMusicStore()
        {
            InitializeComponent();
        }

        private void lvwAvailableItems_ItemSelectionChanged(object sender, ListViewItemSelectionChangedEventArgs e)
        {
            string strFileName = @"C:\Microsoft Visual C# Application Design\" + e.Item.Text + ".jpg";

            if (File.Exists(strFileName))
                pbxSelectedItem.Image = Image.FromFile(strFileName);
            else
                pbxSelectedItem.Image = Image.FromFile(@"C:\Microsoft Visual C# Application Design\MusicItem.jpg");
        }
    }
}

Locating an Element Using its Index

Consider the following XML file named videos.xml:

<?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 Minutes</length>
	<format>DVD</format>
	<rating>PG-13</rating>
    </video>
    <video>
	<title>The Day After Tomorrow</title>
	<director>Roland Emmerich</director>
	<length>124 Minutes</length>
	<format>DVD</format>
	<rating>PG-13</rating>
    </video>
    <video>
	<title>Other People&#039;s Money</title>
	<director>Alan Brunstein</director>
	<length>114 Minutes</length>
	<format>VHS</format>
	<rating>PG-13</rating>
    </video>
</videos>

We know that the XmlNodeList class is equipped with both a method and an indexed propery named Item. Their syntaxes are:

public abstract XmlNode Item(int index);
public virtual XmlNode this[int i] { get; }

These two members allow you to access an element based on its index. Here are examples:

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 VideoCollection1
{
    public partial class Exercise : Form
    {
        public Exercise()
        {
            InitializeComponent();
        }

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

            if (File.Exists(Filename))
            {
                xmlDoc.Load(Filename);

                XmlElement elmRoot = xmlDoc.DocumentElement;
                XmlNodeList lstVideos = elmRoot.ChildNodes;

                MessageBox.Show(lstVideos[1].InnerText);

                MessageBox.Show(lstVideos.Item(3).InnerXml);
            }
        }
    }
}

This would produce:

You can use this characteristic to locate a node. Because XML is very flexible with the names (you can have two child nodes that have the same name) and values (you can have two child nodes that have the same value) of nodes, when creating an XML file, it is your responsibility to create a scheme that would eventually allow you to uniquely identify each element.

Locating an Element Using its Name

To assist you with locating the first child node of a node, the XmlNode class is equipped with an indexed property (named Item) overloaded with two versions. One of the versions is declared as follows:

public virtual XmlElement this[string name] { get; }

This indexed property takes the name of a node as argument. After the property has been called, the parser checks the child nodes of the element on which the property was applied. If the parser finds a node with that name, it returns it as an XmlElement object. Here is an example:

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

    if (File.Exists(Filename))
    {
        xmlDoc.Load(Filename);

        XmlElement elmRoot = xmlDoc.DocumentElement;
        XmlNodeList lstVideos = elmRoot.ChildNodes;

        MessageBox.Show(lstVideos[1]["director"].InnerText);

        MessageBox.Show(lstVideos.Item(3)["format"].InnerXml);
    }
}

Based on the videos.xml file we had earlier, this would produce:

If the node has more than one child with the same name, then it would return the first child with that name. You can use this characteristic to look for, or locate, an element.

Practical Learning: Locating an Element Using its Name

Return to the Solo Music Store form, double-click an unoccupied area of its body

Change the document as follows:

private void InitializeStoreItems()
{
    XmlDocument xdStoreItems = new XmlDocument();
    string strFileName = @"C:\Microsoft Visual C# Application Design\Solo Music Store\StoreItems.xml";

    if (File.Exists(strFileName))
    {
        lbxCategories.Items.Clear();
        lbxSubCategories.Items.Clear();
        lvwAvailableItems.Items.Clear();

        xdStoreItems.Load(strFileName);
        XmlElement xeStoreItem = xdStoreItems.DocumentElement;
        XmlNodeList xnlStoreItems = xeStoreItem.ChildNodes;

        // Display the categories in the left list box
        for (int i = 0; i < xnlStoreItems.Count; i++)
        {
            // Make sure the list box doesn't yet have the category being added
            if (!lbxCategories.Items.Contains(xnlStoreItems[i]["Category"].InnerText))
                lbxCategories.Items.Add(xnlStoreItems[i]["Category"].InnerText);
        }

        pbxSelectedItem.Image = Image.FromFile(@"C:\Microsoft Visual C# Application Design\MusicItem.jpg");
    }
}

private void SoloMusicStore_Load(object sender, EventArgs e)
{
    // If this directory and the sub-directory don't exist, create them
    Directory.CreateDirectory(@"C:\Microsoft Visual C# Application Design\Solo Music Store");
    // If the default musical instrument picture is available, show it.
    // If that picture is not found, the application is
    if (File.Exists(@"C:\Microsoft Visual C# ApplicationDesign\MusicItem.jpg"))
        pbxSelectedItem.Image = Image.FromFile(@"C:\Microsoft Visual C# ApplicationDesign\MusicItem.jpg");
    // Initialize the Categories list box
    InitializeStoreItems();
}

Return to the Solo Music Store form and double-click the Categories list box

Implement the Selected Index Changed event as follows:

private void lbxCategories_SelectedIndexChanged(object sender, EventArgs e)
{
    lbxSubCategories.Items.Clear();
    lvwAvailableItems.Items.Clear();
    XmlDocument xdStoreItems = new XmlDocument();
    string strFileName = @"C:\Microsoft Visual C# Application Design\Solo Music Store\StoreItems.xml";

    if (File.Exists(strFileName))
    {
        xdStoreItems.Load(strFileName);
        XmlElement xeStoreItem = xdStoreItems.DocumentElement;
        XmlNodeList xnlStoreItems = xeStoreItem.ChildNodes;

        // Display the subcategories in the combo box
        for (int i = 0; i < xnlStoreItems.Count; i++)
        {
            // Get only the sub-categories of the selected category
            if (xnlStoreItems[i]["Category"].InnerText == lbxCategories.SelectedItem.ToString())
            {
                if (!lbxSubCategories.Items.Contains(xnlStoreItems[i]["SubCategory"].InnerText))
                    lbxSubCategories.Items.Add(xnlStoreItems[i]["SubCategory"].InnerText);
            }
        }
    }
}

Save all

Locating an Element Using a Tag Name

To assist you with finding a node, the XmlDocument class is equipped with the GetElementByTagName() method which is overloaded with two versions. One of the syntaxes used is:

public virtual XmlNodeList GetElementsByTagName(string name);

This method takes as argument a string. The string must be the name of a node. If at least one node that holds that name exists in the file, this method returns a collection of the nodes with that name. If there is no node with that name, the collection is returned empty and there is no exception thrown.

Here is an example of calling the method:

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

    if (File.Exists(Filename))
    {
        xmlDoc.Load(Filename);

        // Get a reference to the root node
        XmlElement elmRoot = xmlDoc.DocumentElement;

        // Create a list of nodes whose name is Title
        XmlNodeList lstTitles = xmlDoc.GetElementsByTagName("title");
}

Once you have a list of the nodes of a particular criterion, you can then act as you see fit. For example, For example, you can look for a particular node that holds a text of your choice.

Practical Learning: Locating an Element Using its Tag Name

Return to the Solo Music Store form and double-click the Sub-Categories list box

Implement the event as follows:

private void lbxSubCategories_SelectedIndexChanged(object sender, EventArgs e)
{
    lvwAvailableItems.Items.Clear();
    XmlDocument xdStoreItems = new XmlDocument();
    string strFileName = @"C:\Microsoft Visual C# Application Design\Solo Music Store\StoreItems.xml";

    if (File.Exists(strFileName))
    {
        xdStoreItems.Load(strFileName);
        XmlElement xeStoreItem = xdStoreItems.DocumentElement;
        XmlNodeList xnlSubCategories = xeStoreItem.GetElementsByTagName("SubCategory");

        // Display the sub-categories in the combo box
        foreach (XmlNode xnSubCategory in xnlSubCategories)
        {
            // Get only the sub-categories of the selected category
            if (xnSubCategory.InnerText == lbxSubCategories.SelectedItem.ToString())
            {
                ListViewItem lviStoreItem = new ListViewItem(xnSubCategory.PreviousSibling.PreviousSibling.InnerText);
                lviStoreItem.SubItems.Add(xnSubCategory.NextSibling.InnerText);
                lviStoreItem.SubItems.Add(double.Parse(xnSubCategory.NextSibling.NextSibling.InnerText).ToString("F"));

                lvwAvailableItems.Items.Add(lviStoreItem);
            }
        }
    }
}

Display the Store Item Editor form and double-click an unoccupied area of its body

Implement the event as follows:

private void StoreItemEditor_Load(object sender, EventArgs e)
{
    XmlDocument xdStoreItems = new XmlDocument();
    string strFileName = @"C:\Microsoft Visual C# Application Design\Solo Music Store\StoreItems.xml";

    if (File.Exists(strFileName))
    {
        cbxCategories.Items.Clear();
        cbxSubCategories.Items.Clear();
        xdStoreItems.Load(strFileName);

        XmlNodeList xnlCategories = xdStoreItems.DocumentElement.GetElementsByTagName("Category");

        foreach (XmlNode xnCategory in xnlCategories)
        {
            if (!cbxCategories.Items.Contains(xnCategory.FirstChild.InnerText))
                cbxCategories.Items.Add(xnCategory.FirstChild.InnerText);
        }

        pbxSelectedItem.Image = Image.FromFile(@"C:\Microsoft Visual C# Application Design\MusicItem.jpg");
    }
}

Return to the Store Item Editor form and double-click the Find button

Implement the SelectedIndexChanged event as follows:

private void btnFind_Click(object sender, EventArgs e)
{
    bool storeItemFound = false;
    XmlDocument xdStoreItems = new XmlDocument();
    string strFileName = @"C:\Microsoft Visual C# Application Design\Solo Music Store\StoreItems.xml";

    if (string.IsNullOrEmpty(txtItemNumber.Text))
    {
        MessageBox.Show("You must enter a store item number.",
                        "Solo Music Store",
                        MessageBoxButtons.OK, MessageBoxIcon.Information);
        return;
    }

    if (File.Exists(strFileName))
    {
        xdStoreItems.Load(strFileName);
        XmlElement xeStoreItem = xdStoreItems.DocumentElement;
        XmlNodeList xnlStoreItems = xeStoreItem.GetElementsByTagName("ItemNumber");
        string strPictureFile = @"C:\Microsoft Visual C# Application Design\" + txtItemNumber.Text + ".jpg";

        // Check each store item
        foreach (XmlNode xnStoreItem in xnlStoreItems)
        {
            // Check the item number of each store item
            if (xnStoreItem.InnerText == txtItemNumber.Text)
            {
                // If you find the store item, display its values in the controls
                cbxCategories.Text = xnStoreItem.NextSibling.InnerText;
                cbxSubCategories.Text = xnStoreItem.NextSibling.NextSibling.InnerText;
                txtItemName.Text = xnStoreItem.NextSibling.NextSibling.NextSibling.InnerText;
                txtUnitPrice.Text = xnStoreItem.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;

                if (File.Exists(strPictureFile))
                    pbxSelectedItem.Image = Image.FromFile(strPictureFile);
                else
                    pbxSelectedItem.Image = Image.FromFile(@"C:\Microsoft Visual C# Application Design\MusicItem.jpg");

                storeItemFound = true;
            }
        }
    }

    if (storeItemFound == false)
    {
        MessageBox.Show("There is no store item with that number.",
                        "Solo Music Store",
                        MessageBoxButtons.OK, MessageBoxIcon.Information);
    }
}

Return to the Store Item Editor form and double-click the Categories combo box

Implement the SelectedIndexChanged event as follows:

private void cbxCategories_SelectedIndexChanged(object sender, EventArgs e)
{
    XmlDocument xdStoreItems = new XmlDocument();
    string strFileName = @"C:\Microsoft Visual C# Application Design\Solo Music Store\StoreItems.xml";

    if (File.Exists(strFileName))
    {
        xdStoreItems.Load(strFileName);
        XmlElement xeStoreItem = xdStoreItems.DocumentElement;
        XmlNodeList xnlCategories = xeStoreItem.GetElementsByTagName("Category");

        cbxSubCategories.Items.Clear();
        cbxSubCategories.Text = "";

        // Display the sub-categories in the combo box
        foreach (XmlNode xnCategory in xnlCategories)
        {
            // Get only the sub-categories of the selected category
            if (xnCategory.InnerText == cbxCategories.Text)
            {
                if( !cbxSubCategories.Items.Contains(xnCategory.NextSibling.InnerText) )
                    cbxSubCategories.Items.Add(xnCategory.NextSibling.InnerText);
            }
        }
    }
}

Save all

Inserting an Element

Adding an Element as the First Child

Consider the following document saved in a file named Videos.xml:

<?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>
</videos>

To let you add a new element and position it as the first in an XML document, the XmlNode class is equipped with a method named Prepend. Its syntax is:

This method receives an argument as an XmlNode object and adds it on top of the XML document. Here is an example of calling it:

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

public class Exercise : System.Windows.Forms.Form
{
    Button btnAddFirst;

    public Exercise()
    {
        InitializeComponent();
    }

    void InitializeComponent()
    {
        btnAddFirst = new Button();
        btnAddFirst.Text = "Add First";
        btnAddFirst.Location = new Point(12, 12);
        btnAddFirst.Click += new EventHandler(btnAddFirstClick);

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

    void btnAddFirstClick(object sender, EventArgs e)
    {
        string Filename = "../../videos.xml";
        XmlDocument xdVideos = new XmlDocument();

        // Open the XML file
        xdVideos.Load(Filename);

        // Create a new XML element
        XmlElement xeVideo = xdVideos.CreateElement("Video");
        // Specify the child nodes of the element
        xeVideo.InnerXml = "7243 4 92525 9 2" +
                           "<title>Yanni - Tribute</title>" +
                           "<director>George Veras</director>" +
                           "<format>DVD</format>";
        // Add the new element as the first node in the document
        xdVideos.DocumentElement.PrependChild(xeVideo);
        // Save the file
        xdVideos.Save(Filename);
    }
}

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

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <Video>7243 4 92525 9 2
    <title>Yanni - Tribute</title>
    <director>George Veras</director>
    <format>DVD</format>
  </Video>
  <video>
    <title>The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
</videos>

Adding an Element as a Last Child

Once again, consider our Videos.xml file:

<?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 Minutes</length>
	<format>DVD</format>
	<rating>PG-13</rating>
    </video>
    <video>
	<title>The Day After Tomorrow</title>
	<director>Roland Emmerich</director>
	<length>124 Minutes</length>
	<format>DVD</format>
	<rating>PG-13</rating>
    </video>
    <video>
	<title>Other People's Money</title>
	<director>Alan Brunstein</director>
	<length>114 Minutes</length>
	<format>VHS</format>
	<rating>PG-13</rating>
    </video>
</videos>

Imagine you want to add a list of actors of the Her Alibi video. The first action to take is to locate the video, which you can do by calling the XmlDocument.GetElementsByTagName() method applied to a collection of nodes whose names are video. From this list of nodes, you can look for the node whose value is "Her Alibi". Once you have found this element, get a reference to its parent. Then add the new node as a child its parent. This can be done as follows:

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

    if (File.Exists(Filename))
    {
        xmlDoc.Load(Filename);

        // Get a reference to the root node
        XmlElement elmRoot = xmlDoc.DocumentElement;

        // Create a list of nodes whose name is Title
        XmlNodeList lstTitles = xmlDoc.GetElementsByTagName("title");

        // Now you can check each node of the list
        foreach (XmlNode node in lstTitles)
        {
            if (node.InnerText == "Her Alibi")
            {
                // Create an element named Actors
                XmlElement elmNew = xmlDoc.CreateElement("actors");
                XmlNode elmParent = node.ParentNode;
                // Add a new element named Actors to it
                elmParent.AppendChild(elmNew);
                xmlDoc.Save(Filename);
            }
        }
    }
}

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  . . .
  <video>
    <title>Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
    <actors />
  </video>
  . . .
</videos>

This code creates an empty element. If you want to create an element that includes a value, create its text and add that text to the node. Here is an example:

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

    if (File.Exists(Filename))
    {
        xmlDoc.Load(Filename);

        // Get a reference to the root node
        XmlElement elmRoot = xmlDoc.DocumentElement;

        // Create a list of nodes whose name is Title
        XmlNodeList lstTitles = xmlDoc.GetElementsByTagName("title");

        // Now you can check each node of the list
        foreach (XmlNode node in lstTitles)
        {
            // When you get to a node, look for the element's value
            // If you find an element whose value is Her Alibi
            if (node.InnerText == "The Distinguished Gentleman")
            {
                // Create an element named Category
                XmlElement elmNew = xmlDoc.CreateElement("category");
                // Create the text of the new element
                XmlText txtCatetory = xmlDoc.CreateTextNode("Comedy");
                // Get a reference to the parent of the node we have found
                XmlNode elmParent = node.ParentNode;
                // Add the new element to the node we found
                elmParent.AppendChild(elmNew);
                // Specify the text of the new node
                elmParent.LastChild.AppendChild(txtCatetory);
                // Save the file
                xmlDoc.Save(Filename);
            }
        }
    }
}

This would produce:

<?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>
    <category>Comedy</category>
  </video>
  . . .
</videos>

Using the same approach combined with what we learned about adding an item, you can add a new element that itself has child nodes. Here is an example:

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

    if (File.Exists(Filename))
    {
        xmlDoc.Load(Filename);

        // Get a reference to the root node
        XmlElement elmRoot = xmlDoc.DocumentElement;

        // Create a list of nodes whose name is Title
        XmlNodeList lstTitles = xmlDoc.GetElementsByTagName("title");

        // Now you can check each node of the list
        foreach (XmlNode node in lstTitles)
        {
            // When you get to a node, look for the element's value
            // If you find an element whose value is The Day After Tomorrow
            if (node.InnerText == "The Day After Tomorrow")
            {
                // Create an element named Actors
                XmlElement elmNew = xmlDoc.CreateElement("actors");
                // Get a reference to the parent of the node we have found
                XmlNode elmVideo = node.ParentNode;
                // Add the new element to the node we found
                elmVideo.AppendChild(elmNew);

                // Create an element as a child of the new element
                // Specify its name as Actor
                elmNew = xmlDoc.CreateElement("actor");
                // Create the text of the new element
                XmlText txtActor = xmlDoc.CreateTextNode("Dennis Quaid");
                // Add the new Actor element to the Actors node
                elmVideo.LastChild.AppendChild(elmNew);
                // Specify the text of the new node
                elmVideo.LastChild.LastChild.AppendChild(txtActor);

                // In the same way, add the other Actor nodes
                elmNew = xmlDoc.CreateElement("actor");
                txtActor = xmlDoc.CreateTextNode("Jake Gyllenhaal");
                elmVideo.LastChild.AppendChild(elmNew);
                elmVideo.LastChild.LastChild.AppendChild(txtActor);

                elmNew = xmlDoc.CreateElement("actor");
                txtActor = xmlDoc.CreateTextNode("Emmy Rossum");
                elmVideo.LastChild.AppendChild(elmNew);
                elmVideo.LastChild.LastChild.AppendChild(txtActor);

                elmNew = xmlDoc.CreateElement("actor");
                txtActor = xmlDoc.CreateTextNode("Dash Mihok");
                elmVideo.LastChild.AppendChild(elmNew);
                elmVideo.LastChild.LastChild.AppendChild(txtActor);

                // Save the file
                xmlDoc.Save(Filename);
            }
        }
    }
}

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  . . .
  <video>
    <title>The Day After Tomorrow</title>
    <director>Roland Emmerich</director>
    <length>124 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
    <actors>
      <actor>Dennis Quaid</actor>
      <actor>Jake Gyllenhaal</actor>
      <actor>Emmy Rossum</actor>
      <actor>Dash Mihok</actor>
    </actors>
  </video>
</videos>

You can also insert one or more elements as children of an existing node after locating that node. Here is an example:

XML File

<?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>
    <category>Comedy</category>
  </video>
  <video>
    <title>Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Mins</length>
    <format>DVD</format>
    <rating>PG-13</rating>
    <actors />
  </video>
</videos>

Code Fragment:

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

    if (File.Exists(Filename))
    {
        xmlDoc.Load(Filename);

        // Get a reference to the root node
        XmlElement elmRoot = xmlDoc.DocumentElement;

        // Create a list of nodes whose name is Title
        XmlNodeList lstTitles = xmlDoc.GetElementsByTagName("title");

        // Now you can check each node of the list
        foreach (XmlNode node in lstTitles)
        {
            // When you get to a node, look for the element's value
            // If you find an element whose value is Her Alibi
            if (node.InnerText == "Her Alibi")
            {
                // Get a reference to the video node that is 
                // the parent of the video titled Her Alibi
                XmlNode elmVideo = node.ParentNode;

                // Create a list of the child nodes of the Her alibi video
                XmlNodeList lstActors = elmVideo.ChildNodes;

                // Visit each item of the collection
                // looking for an element named Actors
                foreach (XmlNode nodActor in lstActors)
                {
                    // If you find an element named Actors
                    if (nodActor.Name == "actors")
                    {
                        // Create a new element named Actor
                        // Specify its name as Actor
                        XmlElement elmNew = xmlDoc.CreateElement("actor");
                        // Create the text of the new element
                        XmlText txtActor = xmlDoc.CreateTextNode("Tom Selleck");
                        // Add the new Actor element to the Actors node
                        elmVideo.LastChild.AppendChild(elmNew);
                        // Specify the text of the new node
                        elmVideo.LastChild.LastChild.AppendChild(txtActor);

                        // Add other Actor nodes
                        elmNew = xmlDoc.CreateElement("actor");
                        txtActor = xmlDoc.CreateTextNode("Paulina Porizkova");
                        elmVideo.LastChild.AppendChild(elmNew);
                        elmVideo.LastChild.LastChild.AppendChild(txtActor);

                        elmNew = xmlDoc.CreateElement("actor");
                        txtActor = xmlDoc.CreateTextNode("William Daniels");
                        elmVideo.LastChild.AppendChild(elmNew);
                        elmVideo.LastChild.LastChild.AppendChild(txtActor);

                        // Save the file
                        xmlDoc.Save(Filename);

                        // Stop, in this example, we don't expect another Actors node
                        break;
                    }
                }
            }
        }
    }
}

This would produce:

<?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>
    <category>Comedy</category>
  </video>
  <video>
    <title>Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
    <actors>
      <actor>Tom Selleck</actor>
      <actor>Paulina Porizkova</actor>
      <actor>William Daniels</actor>
    </actors>
  </video>
</videos>

Inserting an Element Referencing a Sibling

Instead of simply adding a new node at the end of child nodes, you can specify any other position you want. For example, you may want the new node to precede an existing child node. To support this operation, the XmlNode class provides the InsertBefore() method. Its syntax is:

public virtual XmlNode InsertBefore(XmlNode newChild, XmlNode refChild);

The first argument of this method is the new node that will be added. The second argument is the sibling that will succeed the new node. Consider the following version of our Videos.xml file:

<?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>
      	<category>Comedy</category>
    </video>
    <video>
	<title>Fatal Attraction</title>
	<director>Adrian Lyne</director>
	<length>119 Minutes</length>
	<format>DVD</format>
	<rating>R</rating>
    </video>
</videos>

Imagine you want to create a new category element below the director element whose name is Adrian Lyne. You can first get a list of videos. Inside of each video, check the nodes and find out whether the video has a director node whose text is Adrian Lyne. Once you find that node, you can add the new element after it. Here is an example:

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

    if (File.Exists(Filename))
    {
        xmlDoc.Load(Filename);

        // Get a reference to the root node
        XmlElement elmRoot = xmlDoc.DocumentElement;

        // Create a list of the videos
        XmlNodeList lstVideos = xmlDoc.GetElementsByTagName("video");

        // visit each video
        foreach (XmlNode node in lstVideos)
        {
            // Within a video, create a list of its children
            XmlNodeList lstChildren = node.ChildNodes;

            // Visit each child node
            foreach (XmlNode dir in lstChildren)
            {
                // If the child node is (a director and its name is) Adrian Lyne
                if (dir.InnerText == "Adrian Lyne")
                {
                    // Create an element named Category
                    XmlElement elmNew = xmlDoc.CreateElement("category");
                    // Specify the text of the new element
                    elmNew.InnerText = "Drama";

                    // Insert the new node below the Adrian Lyne node Director
                    node.InsertAfter(elmNew, dir);

                    // Save the file
                    xmlDoc.Save(Filename);

                    // Stop
                    break;
                }
            }
        }
    }
}

This would produce:

<?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>
    <category>Comedy</category>
  </video>
  <video>
    <title>Fatal Attraction</title>
    <director>Adrian Lyne</director>
    <category>Drama</category>
    <length>119 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
</videos>

In the same way, you can insert a new node after a child of a child (or of a child of a child of a child) of any node.

If you want to new node to be positioned after an existing child node, you can call the XmlNode.InsertAfter() method. Its syntax is:

public virtual XmlNode InsertAfter(XmlNode newChild, XmlNode refChild);

Practical Learning: Inserting an XML Element

Display the Solo Music Store form and double-click the New Store Item button

Implement the event as follows:

private void btnNewStoreItem_Click(object sender, EventArgs e)
{
    int ItemNumber;
    double UnitPrice = 0D;
    string Category, SubCategory, ItemName;

    XmlDocument xdStoreItems = new XmlDocument();
    StoreItemEditor editor = new StoreItemEditor();
    string strFileName = @"C:\Microsoft Visual C# Application Design\Solo Music Store\StoreItems.xml";

    // Make sure the user provides the item number, the category, the sub-category,
    // the name (or short description), and the price of the item
    if (editor.ShowDialog() == DialogResult.OK)
    {
        if (string.IsNullOrEmpty(editor.txtItemNumber.Text) ||
            string.IsNullOrEmpty(editor.cbxCategories.Text) ||
            string.IsNullOrEmpty(editor.cbxSubCategories.Text) ||
            string.IsNullOrEmpty(editor.txtItemName.Text))
        {
            MessageBox.Show("You must provide all the information about the new item. " +
                            "This includes the item number, its category, its sub-category, " +
                            "its name (or short description), and its price.",
                            "Solo Music Store",
                            MessageBoxButtons.OK, MessageBoxIcon.Information);
            return;
        }

        // Get the values that were provided for the new store item
        ItemNumber = int.Parse(editor.txtItemNumber.Text);
        Category = editor.cbxCategories.Text;
        SubCategory = editor.cbxSubCategories.Text;
        ItemName = editor.txtItemName.Text;
        UnitPrice = double.Parse(editor.txtUnitPrice.Text);

        // Find out if the file exists already
        // If it doesn't, then create it
        if (!File.Exists(strFileName))
        {
            xdStoreItems.LoadXml("<?xml version=\"1.0\" encoding=\"utf-8\"?>" +
                                    "<StoreItems></StoreItems>");
            xdStoreItems.Save(strFileName);
        }

        // Open the XML file of the store items
        xdStoreItems.Load(strFileName);

        // We will use this variable to find out whether the category
        // being added exists already in the Store Items document
        bool categoryFound = false;
        // Get all the store items that have a Category node
        XmlNodeList xnlCategories = xdStoreItems.DocumentElement.GetElementsByTagName("Category");

        // Since we will create a new store item, let's initialize its new node
        XmlElement xeStoreItem = xdStoreItems.CreateElement("StoreItem");

        xeStoreItem.InnerXml = "<ItemNumber>" + ItemNumber.ToString() + "</ItemNumber>" +
                               "<Category>" + Category + "</Category>" +
                               "<SubCategory>" + SubCategory + "</SubCategory>" +
                               "<ItemName>" + ItemName + "</ItemName>" +
                               "<UnitPrice>" + UnitPrice.ToString() + "</UnitPrice>";

        // Check each store item
        foreach (XmlNode xnCategory in xnlCategories)
        {
            // If you find the same category, ...
            if (xnCategory.InnerText == Category)
            {
                // Now that we found a category, check the categories.
                // If you find the same sub-category, ...
                if (xnCategory.NextSibling.InnerText == SubCategory)
                {
                    // Now that we have the same sub-category, compare it to the current sub-category.
                    // If the current sub-category alphabetically comes before the sub-category
                    // of the new store item, insert the new one before the existing one
                    if (string.Compare(xnCategory.InnerText, Category) < 0)
                        xdStoreItems.DocumentElement.InsertBefore(xeStoreItem, xnCategory.ParentNode);
                    else // Otherwise, add it after
                        xdStoreItems.DocumentElement.InsertAfter(xeStoreItem, xnCategory.ParentNode);
                }
                else
                {
                    // If the new sub-category was not found in the document, compare its item number
                    // to that of the existing store item.
                    // If the item number of the existing store item is higher than that of 
                    // the new store item, add the new store item before the existing one
                    if (int.Parse(xnCategory.PreviousSibling.InnerText) > ItemNumber)
                        xdStoreItems.DocumentElement.InsertBefore(xeStoreItem, xnCategory.ParentNode);
                    else // Otherwise, add it after
                        xdStoreItems.DocumentElement.InsertAfter(xeStoreItem, xnCategory.ParentNode);
                }

                categoryFound = true;
                break;
            }
        }

        // If the new category was not found, ...
        if (categoryFound == false)
        {
            // If there are already five store items in the document,
            // add the new one as the first
            if (xdStoreItems.ChildNodes.Count < 5)
                xdStoreItems.DocumentElement.PrependChild(xeStoreItem);
            else // Otherwise, add the new store item the the last element
                xdStoreItems.DocumentElement.AppendChild(xeStoreItem);
        }

        // Now the the new store item has been added or inserted, save the XML file
        xdStoreItems.Save(strFileName);

        InitializeStoreItems();
    }
}

Save all

Updating an Element

The .NET Framework implementation of XML provides various options to change the aspect, structure, or values, of an element. For example, you can use the same logic used in collection classes. This consists of locating a node and simply changing its value. Here is an example:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video>
    <title>Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video>
    <title>The Day After Tomorrow</title>
    <director>Roland Emmerich</director>
    <length>124 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>
----------------------------------------------------------------
using System;
using System.Drawing;
using System.Windows.Forms;
using System.Xml;
using System.IO;

public class Exercise : System.Windows.Forms.Form
{
    Button btnUpdate;

    public Exercise()
    {
        InitializeComponent();
    }

    void InitializeComponent()
    {
        btnUpdate = new Button();
        btnUpdate.Text = "Update";
        btnUpdate.Location = new Point(12, 12);
        btnUpdate.Click += new EventHandler(btnUpdateClick);

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

    void btnUpdateClick(object sender, EventArgs e)
    {
        string Filename = "../../videos.xml";
        XmlDocument xdVideos = new XmlDocument();

        // Open the XML file
        xdVideos.Load(Filename);
        XmlNodeList xnlVideos = xdVideos.DocumentElement.GetElementsByTagName("title");

        foreach (XmlNode xnVideo in xnlVideos)
        {
            if(xnVideo.InnerText.Contains("Day After Tomorrow") )
            {
                xnVideo.ParentNode.InnerXml = "<title>Day After Tomorrow(The)</title>" +
		                              "<director>Roland Emmerich</director>" +
        		                      "<year>2004</year>" +
                		              "<length>124 Minutes</length>" +
                        		      "<format>DVD</format>" +
                                	      "<rating>PG-13</rating>";
                xdVideos.Save(Filename);
                break;
            }
        }
    }
}

public class Program
{
    static int Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        System.Windows.Forms.Application.Run(new Exercise());
        return 0;
    }
}
----------------------------------------------------------------
<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video>
    <title>Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video>
    <title>Day After Tomorrow(The)</title>
    <director>Roland Emmerich</director>
    <year>2004</year>
    <length>124</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

On the other hand, the XmlNode class is equipped with a method named ReplaceChild. Its syntax is:

To use this method, first locate an element and get its reference. Then change the values or child nodes you want, and finally replace the original value with the new version. In reality, and as its name implies, it is not the primary purpose of this method to edit or update an element. The role of this method is to use one node in place of another.

Practical Learning: Updating an XML Element

Return to the Solo Music Store form and double-click the Update Store Item button

Implement the event as follows:

private void btnUpdateStoreItem_Click(object sender, EventArgs e)
{
    int ItemNumber;
    double UnitPrice = 0D;
    string Category, SubCategory, ItemName;

    XmlDocument xdStoreItems = new XmlDocument();
    StoreItemEditor editor = new StoreItemEditor();
    string strFileName = @"C:\Microsoft Visual C# Application Design\Solo Music Store\StoreItems.xml";

    editor.btnFind.Visible = true;


    if (editor.ShowDialog() == DialogResult.OK)
    {
        if (string.IsNullOrEmpty(editor.txtItemNumber.Text) ||
            string.IsNullOrEmpty(editor.cbxCategories.Text) ||
            string.IsNullOrEmpty(editor.cbxSubCategories.Text) ||
            string.IsNullOrEmpty(editor.txtItemName.Text))
        {
            MessageBox.Show("You must provide all the information about the new item. " +
                            "This includes the item number, its category, its sub-category, " +
                            "its name (or short description), and its price.",
                            "Solo Music Store",
                            MessageBoxButtons.OK, MessageBoxIcon.Information);
            return;
        }

        // Get the values that were provided for the new store item
        ItemNumber = int.Parse(editor.txtItemNumber.Text);
        Category = editor.cbxCategories.Text;
        SubCategory = editor.cbxSubCategories.Text;
        ItemName = editor.txtItemName.Text;
        UnitPrice = double.Parse(editor.txtUnitPrice.Text);

        // Find out if the file exists already
        // If it doesn't, then create it
        if (!File.Exists(strFileName))
        {
            MessageBox.Show("There is no store items inventory to update.",
                            "Solo Music Store",
                            MessageBoxButtons.OK, MessageBoxIcon.Information);
            return;
        }

        // Open the XML file of the store items
        xdStoreItems.Load(strFileName);

        // Get all the store items that have a Category node
        XmlNodeList xnlItemNumbers = xdStoreItems.DocumentElement.GetElementsByTagName("ItemNumber");

        // Since we will create a new store item, let's initialize its new node
        XmlElement xeStoreItem = xdStoreItems.CreateElement("StoreItem");

        xeStoreItem.InnerXml = "<ItemNumber>" + ItemNumber.ToString() + "</ItemNumber>" +
                               "<Category>" + Category + "</Category>" +
                               "<SubCategory>" + SubCategory + "</SubCategory>" +
                               "<ItemName>" + ItemName + "</ItemName>" +
                               "<UnitPrice>" + UnitPrice.ToString() + "</UnitPrice>";

        // Check each store item
        foreach (XmlNode xnStoreItem in xnlItemNumbers)
        {
            // If you find the same item number, ...
            if (int.Parse(xnStoreItem.InnerText) == ItemNumber)
            {
                xdStoreItems.DocumentElement.ReplaceChild(xeStoreItem, xnStoreItem.ParentNode);
                break;
            }
        }

        // Now the the new store item has been added or inserted, save the XML file
        xdStoreItems.Save(strFileName);

        InitializeStoreItems();
    }
}

Deleting Elements

Deleting an Element

If you have a node you don't want or don't need anymore in the file, you can delete it. To delete a node, the XmlNode class provides the RemoveChild() method. Its syntax is:

public virtual XmlNode RemoveChild(XmlNode oldChild);

This method takes as argument the node to delete. If the node exists, it would be deleted and the method would return the node that was deleted. If the node does not exist, nothing would happen. To effectively use this method, you should first locate the particular node you want to delete. You can look for it using any of the logics we have applied so far. Once you find the node, you can then delete it. Imagine you want to delete a node whose name is Director and whose value is Bruce Beresford. Here is an example of calling this method to perform the operation:

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

    if (File.Exists(Filename))
    {
        xmlDoc.Load(Filename);

        // Get a reference to the root node
        XmlElement elmRoot = xmlDoc.DocumentElement;

        // Create a list of the videos
        XmlNodeList lstVideos = xmlDoc.GetElementsByTagName("video");

        // visit each video
        foreach (XmlNode node in lstVideos)
        {
            // Within a video, get a list of its children
            XmlNodeList lstChildren = node.ChildNodes;

            // Visit each child node
            foreach (XmlNode dir in lstChildren)
            {
                // If the child node is Bruce Beresford
                if (dir.InnerText == "Adrian Lyne")
                {
                    node.RemoveChild(dir);

                    // Save the file
                    xmlDoc.Save(Filename);

                    // Stop
                    break;
                }
            }
        }
    }
}

Practical Learning: Deleting an XML Element

Return to the Solo Music Store form and double-click the Delete Store Item button

Implement the event as follows:

private void btnDeleteStoreItem_Click(object sender, EventArgs e)
{
    XmlDocument xdStoreItems = new XmlDocument();
    StoreItemEditor editor = new StoreItemEditor();
    string strFileName = @"C:\Microsoft Visual C# Application Design\Solo Music Store\StoreItems.xml";

    editor.btnFind.Visible = true;


    if (editor.ShowDialog() == DialogResult.OK)
    {
        if (string.IsNullOrEmpty(editor.txtItemNumber.Text))
        {
            MessageBox.Show("You must specify the item number of the item you want to delete.",
                            "Solo Music Store",
                            MessageBoxButtons.OK, MessageBoxIcon.Information);
            return;
        }

        // Find out if the file exists already
        // If it doesn't, then create it
        if (!File.Exists(strFileName))
        {
            MessageBox.Show("There is no store items inventory to update.",
                            "Solo Music Store",
                            MessageBoxButtons.OK, MessageBoxIcon.Information);
            return;
        }

        // Open the XML file of the store items
        xdStoreItems.Load(strFileName);

        // Get all the store items that have a Category node
        XmlNodeList xnlItemNumbers = xdStoreItems.DocumentElement.GetElementsByTagName("ItemNumber");

        // Check each store item
        foreach (XmlNode xnStoreItem in xnlItemNumbers)
        {
            // If you find the same item number, ...
            if (xnStoreItem.InnerText == editor.txtItemNumber.Text)
            {
                if (MessageBox.Show("Are you sure you want to remove this item from the store inventory?",
                                    "Solo Music Store",
                                    MessageBoxButtons.YesNo, MessageBoxIcon.Question) == System.Windows.Forms.DialogResult.Yes)
                {
                    xdStoreItems.DocumentElement.RemoveChild(xnStoreItem.ParentNode);
                    break;
                }
            }
        }

        // Now the the new store item has been added or inserted, save the XML file
        xdStoreItems.Save(strFileName);

        InitializeStoreItems();
    }
}

Return to the Solo Music Store and double-click the Close button

Implement the event as follows:

private void btnClose_Click(object sender, EventArgs e)
{
    Close();
}

Execute the application

Create some records with the following values:

Item #	Category	Sub-Category	Item Name	Unit Price
930485	Keyboards	Synthesizers	Roland JUNO-Gi Synthesizer	780.00
485948	Drums	Acoustic Drum Sets	Sound Percussion Complete 5-Piece Drum Set with Cymbals & Hardware	350.00
920820	Miscellaneous	DJ Accessories	Pioneer RMX-1000 Remix Station Black	650.00
406033	Guitars	Electric Guitars	B.C. Rich Pro X Custom Special X3 Mockingbird Electric Guitar Tobacco Burst	395.95
358460	Bass	Electric Basses	Fender Deluxe P Bass Special 4-String Bass	695.95
724799	Accessories	Cables	Monster Cable S-100 XLR Microphone Cable	14.00
582693	Keyboards	Organs	Roland VK-88 Combo Organ	5695.00
350250	Guitars	Acoustic Guitars	FA Acoustic	120.00
332085	Miscellaneous	Multitrack Recorders	Zoom R8 8-Track SD Recorder, Sampler & USB Interface	295.75
836360	Brass Instruments	Trumpets	Brasswind Model II Student Bb Trumpet	180.00
415158	Drums	Electronic Drum Sets	Simmons SD5X Electronic Drum Set	425.75
886182	Keyboards	Synthesizers	Roland Jupiter-80 Synthesizer	3525.00
516080	Guitars	Acoustic-Electric Guitars	Taylor 214ce Rosewood/Spruce Grand Auditorium Acoustic-Electric Guitar	1000.00
536949	Live Sound	Packages	Phonic Powerpod 620 Plus / S710 PA Package	295.95
414913	Woodwinds	Saxophones	Allora Vienna Series Intermediate Alto Saxophone	795.95
161553	Miscellaneous	Multitrack Recorders	TASCAM DP-32 Digital 32-Track Portastudio	795.95
355862	Guitars	Electric Guitars	PRS SE Custom 24 Electric Guitar	595.85
293488	Bass	Electric Basses	Ibanez SR1206E 6-String Electric Bass Vintage	1250.00
330088	Keyboards	Synthesizers	Korg MicroKORG Synthesizer/Vocoder	415.55
115599	Accessories	Cables	Right-On Cable	98.95
402882	Accessories	Cables	Monster Cable Digilink 5 Pin MIDI Cable	9.95
937528	Guitars	Electric Guitars	ESP LTD EC-256FM Electric Guitar	395.95
355582	Miscellaneous	Speakers	Peavey PR 12 Speaker Pair	360.00
140864	Brass Instruments	Trombones	Allora Student Series Bb Trombone Model AATB-102	215.50
173031	Drums	Hi-Hat Cymbals	Zildjian ZXT Solid Hi-Hat Cymbal (Pair) 14 Inches	145.75
217790	Live Sound	Microphones	MXL 3000 Mic Bundle	245.85
676184	Keyboards	Pianos	Williams Overture 88 Key Digital Piano	595.95
406266	Live Sound	Microphones	MXL V63M Condenser Studio Microphone	99.95
357020	Drums	Acoustic Drum Sets	Ludwig Breakbeats by Questlove 4-Piece Shell Pack Azure Sparkle	395.95
486021	Keyboards	Synthesizers	Roland BK-9 Backing Keyboard	2495.85
686659	Bass	Electric Basses	Fender American Deluxe Jazz Bass V 5-String Electric Bass	1795.95
583746	Guitars	Acoustic Guitars	Yamaha FG700S Folk Acoustic Guitar	225.50
388835	Drums	Acoustic Drum Sets	Gretsch Drums Energy 5-Piece Drum Set with Hardware and Sabian SBR Cymbals	695.95
258395	Accessories	Cables	Monster Cable Performer 500 Speaker Cable	21.50
769138	Live Sound	Amplifiers	Acoustic Lead Guitar Series G120 DSP 120W Guitar Combo Amp	199.95
275157	Keyboards	Synthesizers	Yamaha S90XS 88-Key Balanced Weighted Hammer Action Synthesizer	2450.00
843814	Guitars	Acoustic Guitars	Fender CD100 12-String Acoustic Guitar Natural	255.50
281141	Orchestra	Violins	Florea Recital II Violin Outfit	150.00
966060	Drums	Electronic Drum Sets	Simmons SDXpress2 Compact 5-Piece Electronic Drum Kit	225.50
559606	Live Sound	Packages	Gear One PA2400 / Kustom KPC15 Mains and Monitors Package	696.95
725504	Miscellaneous	Mixers	Nady PMX-1600 16 Channel/4 Bus Powered Mixer w/DSP Effects	649.95
972405	Guitars	Electric Guitars	ESP LTD EC-256FM Electric Guitar	395.95
434426	Keyboards	Pianos	Suzuki S-350 Mini Grand Digital Piano	2500.00
259592	Accessories	Cables	Mogami Gold Instrument Cable Angled - Straight Cable	42.25
382730	Orchestra	Violins	Mendini 4/4 MV300 Solid Wood Violin in Satin Finish	59.95
849926	Bass	Electric Basses	Squier by Fender Vintage Modified Jazz Bass ''77, Amber	325.50
207925	Woodwinds	Saxophones	Yamaha YAS-62III Professional Alto Saxophone	2950.00

On the Solo Music Store form, click the Update Store Item button
In the item # text box, type 350250 and press Tab
Change its name to Fender FA-100 Acoustic Guitar
Change its price to 125.75
Click Update Store Item and click Yes
On the Solo Music Store form, click the Delete Store Item button
In the item # text box, type 115599 and press Tab
Click Delete Store Item and click Yes
Close the forms and return to your programming environment

Clearing an Element of its Children

To delete all child nodes of a node, you can call the XmlNode.RemoveAll() method. Its syntax is:

public virtual void RemoveAll();

When called, this method will remove all child nodes, if any, of their parent node. Here is an example of calling it:

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

public class Exercise : System.Windows.Forms.Form
{
    Button btnDeleteEverything;

    public Exercise()
    {
        InitializeComponent();
    }

    void InitializeComponent()
    {
        btnDeleteEverything = new Button();
        btnDeleteEverything.Width = 120;
        btnDeleteEverything.Text = "Delete Everything";
        btnDeleteEverything.Location = new Point(12, 12);
        btnDeleteEverything.Click += new EventHandler(btnDeleteEverythingClick);

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

    void btnDeleteEverythingClick(object sender, EventArgs e)
    {
        string Filename = "../../videos.xml";
        XmlDocument xdVideos = new XmlDocument();

        // Open the XML file
        xdVideos.Load(Filename);
        // Clear the XML document
        xdVideos.DocumentElement.RemoveAll();
        // Save the XML document
        xdVideos.Save(Filename);
    }
}

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

This would produce:

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

Application