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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. In our Videos.xml example, 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 Child Nodes

To support the child nodes of a particular node, the XmlNode class is equipped with the ChildNodes property. To identify the collection of child nodes of a node, the .NET Framework provides the XmlNodeList class. Therefore, the ChildNodes property of an XmlNode object is of type XmlNodeList. This 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:

XML Nodes
using System;
using System.IO;
using System.Xml;

namespace VideoCollection
{
    class Program
    {
        static int Main(string[] args)
        {
            string strFilename = "Videos.xml";
            XmlDocument xmlDoc = new XmlDocument();

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

                Console.WriteLine("The root element contains {0} nodes",
                                  lstVideos.Count);
            }
            else
                Console.WriteLine("The file {0} could not be located",
                                  strFilename);

            Console.WriteLine();
            return 0;
        }
    }
}

This would produce:

The root element contains 3 nodes

Press any key to continue . . .

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

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:

using System;
using System.IO;
using System.Xml;

namespace VideoCollection
{
    class Program
    {
        static int Main(string[] args)
        {
            string strFilename = "Videos.xml";
            XmlDocument xmlDoc = new XmlDocument();

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

                Console.WriteLine(lstVideos[2]);;
 
            }
            else
                Console.WriteLine("The file {0} could not be located",
                                  strFilename);

            Console.WriteLine();
            return 0;
        }
    }
}

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:

using System;
using System.IO;
using System.Xml;

namespace VideoCollection
{
    class Program
    {
        static int Main(string[] args)
        {
            string strFilename = "Videos.xml";
            XmlDocument xmlDoc = new XmlDocument();

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

                for (int i = 0; i < lstVideos.Count; i++)
                    Console.WriteLine("{0}",lstVideos[i].InnerText );
            }
            else
                Console.WriteLine("The file {0} could not be located",
                                  strFilename);

            Console.WriteLine();
            return 0;
        }
    }
}

This would produce:

The Distinguished GentlemanJonathan Lynn112 MinutesDVDR
Her AlibiBruce Beresford94 MinsDVDPG-13
Chalte ChalteAziz Mirza145 MinsDVDN/R

Press any key to continue . . .

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:

using System;
using System.IO;
using System.Xml;

namespace VideoCollection
{
    class Program
    {
        static int Main(string[] args)
        {
            string strFilename = "Videos.xml";
            XmlDocument xmlDoc = new XmlDocument();

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

                foreach(XmlNode node in lstVideos)
                    Console.WriteLine("{0}", node);
            }
            else
                Console.WriteLine("The file {0} could not be located",
                                  strFilename);

            Console.WriteLine();
            return 0;
        }
    }
}

This would produce:

System.Xml.XmlElement
System.Xml.XmlElement
System.Xml.XmlElement

Press any key to continue . . .

To better manage and manipulate the nodes of a collection of nodes, you must be able to access the desired node. The XmlNode combined with the XmlNodeList classes 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 doesn't 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.IO;
using System.Xml;

namespace VideoCollection
{
    class Program
    {
        static int Main(string[] args)
        {
            string strFilename = "Videos.xml";
            XmlDocument xmlDoc = new XmlDocument();

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

                for (int i = 0; i < lstVideos.Count; i++)
                    Console.WriteLine("{0}",
                        lstVideos[i].FirstChild.InnerText );
            }
            else
                Console.WriteLine("The file {0} could not be located",
                                  strFilename);

            Console.WriteLine();
            return 0;
        }
    }
}

This would produce:

The Distinguished Gentleman
Her Alibi
Chalte Chalte

Press any key to continue . . .

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:

using System;
using System.IO;
using System.Xml;

namespace VideoCollection
{
    class Program
    {
        static int Main(string[] args)
        {
            string strFilename = "Videos.xml";
            XmlDocument xmlDoc = new XmlDocument();

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

                for (int i = 0; i < lstVideos.Count; i++)
                    Console.WriteLine("{0}",
                        lstVideos[i].InnerText );
            }
            else
                Console.WriteLine("The file {0} could not be located",
                                  strFilename);

            Console.WriteLine();
            return 0;
        }
    }
}

This would produce:

The Distinguished Gentleman
Jonathan Lynn
112 Minutes
DVD
R

Press any key to continue . . .

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 loop 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:

using System;
using System.IO;
using System.Xml;

namespace VideoCollection
{
    class Program
    {
        static int Main(string[] args)
        {
            string strFilename = "Videos.xml";
            XmlDocument xmlDoc = new XmlDocument();

            if (File.Exists(strFilename))
            {
                xmlDoc.Load(strFilename);
                // Locate the root node and 
                // get a reference to its first child
                XmlNode node = xmlDoc.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++)
                            Console.WriteLine("{0}",
                                lstActors[j].InnerText);
                    }
                }
            }
            else
                Console.WriteLine("The file {0} could not be located",
                                  strFilename);

            Console.WriteLine();
            return 0;
        }
    }
}

This would produce:

Eddie Murphy
Lane Smith
Sheryl Lee Ralph
Joe Don Baker
Victoria Rowell

Press any key to continue . . .

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:

using System;
using System.IO;
using System.Xml;

namespace VideoCollection
{
    class Program
    {
        static int Main(string[] args)
        {
            string strFilename = "Videos.xml";
            XmlDocument xmlDoc = new XmlDocument();

            if (File.Exists(strFilename))
            {
                xmlDoc.Load(strFilename);
                // Locate the root node and 
                // get a reference to its first child
                XmlNode node = xmlDoc.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++)
                            Console.WriteLine("{0}",
                                lstActors[j].InnerText);
                    }
                }
            }
            else
                Console.WriteLine("The file {0} could not be located",
                                  strFilename);

            Console.WriteLine();
            return 0;
        }
    }
}

This would produce:

Eddie Murphy

Press any key to continue . . .

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, Actors, 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};

 

 

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