Fundamentals of Attributes

Introduction

The element and the attribute have these in common:

• Both (must) have a name
• Each may or may not have a value

The differences between an element and an attribute are:

• An attribute is considered a characteristic of an element. This means that an attribute belongs to an element
• While an element can have one or more attributes, an attribute can neither have an element nor have another or more attributes
• An attribute must be created in the start-tag of an element
• An element cannot be defined as part of an attribute. That is, an attribute is subject to an element and an attribute doesn't own the attribute

Imagine you have an ISBN element as a child of a video element as follows:

<video>
    <ISBN>0-7888-1623-3</ISBN>
</video>

An attribute must be created inside the start-tag of an element. To manually create an attribute, type the left angle bracket of the element, followed by the name of the element, an empty space, and the name of the attribute. The name follows the same rules we defined for names in XML.

An attribute should have a value that can be used to distinguish it. To specify the name of an attribute, assign a value as a string to its name. In the case of the above code fragment, since ISBN is simply a child of the video element, you can change the ISBN element to become an attribute of the video element as follows:

<video ISBN="0-7888-1623-3">

Now, ISBN is an attribute of the video element.

In the .NET Framework, an attribute is represented by the XmlAttribute class. Like all nodes, this class is based on the XmlNode class. The name of an attribute is represented by its (read-only) Name property. The value of an attribute is represented by its Value property. Besides Value, you can also use the XmlAttribute.InnerText or the XmlAttribute.InnerXml properties to access the text of an attribute.

An element can have 0, one, or more attributes. The attributes of an element are stored in the Attributes property of an XmlElement object. The XmlElement.Attributes property is based on a class called XmlAttributeCollection. The XmlAttributeCollection class is based on the XmlNamedNodeMap class.

Before performing an attribute-related operation on an element, to find out whether the element has any attribute, you can check the value of the HasAttributes Boolean property of its XmlElement element. If this property produces a true value, then the element has at least one attribute. Otherwise, the element does not have any attribute.

While a certain element may have an attribute, a sibling element with the same name may not have an attribute or may have a completely different type of attribute. Here is an XML file with attributes in some elements:

<?xml version="1.0" encoding="utf-8" ?>
<videos>
    <video ISBN="0-7888-1623-3">
	<title Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
	<director>Jonathan Lynn</director>
	<length>112 Minutes</length>
	<format>DVD</format>
	<rating>R</rating>
    </video>
    <video>
	<title WrittenBy="Charlie Peter">Her Alibi</title>
	<director>Bruce Beresford</director>
	<length>94 Mins</length>
	<format>DVD</format>
	<rating>PG-13</rating>
    </video>
</videos>

Remember that you can include white spaces to make your code easy to read. This means that you can type an attribute on the next line of its element's name. In Lesson 7, we saw that every element must be closed. We saw that we could close an element with an end-tag as follows:

<video><ISBN>0-7888-1623-3</ISBN></video>

We also saw that we could close an element locally as follows: <video />. If you create an attribute in an empty element, you can also close it by typing the indicative forward slash before the right angle bracket and after an empty space. Here is an example:

<video ISBN="0-7888-1623-3" />

As mentioned already, an attribute primarily belongs to an element. This means that, when creating an attribute, you must specify what element it would belong to. To support the attributes of an element, the XmlElement class is equipped with the SetAttribute() method which is overloaded in two versions. The first version of this method uses the following syntax:

Public Overridable Sub SetAttribute(name As String, value As String)

The first argument is the name of the new attribute and the second argument will be its text. Before adding an attribute, you should first identify its parent element. Here is an example that adds an attribute to the root element:

Imports System.Xml
Imports System.IO

Public Class Exercise

    Private Sub btnDocument_Click(ByVal sender As System.Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnDocument.Click
        Dim Filename As String = "videos.xml"
        Dim DocumentElement As XmlDocument = New XmlDocument

        If File.Exists(Filename) Then
            ' Open the XML file
            DocumentElement.Load(Filename)

            ' Create an attribute and add it to the root element
            DocumentElement.DocumentElement.SetAttribute("FileDesc", _
                               "Personal Video Collection")
            DocumentElement.Save("videos.xml")
        End If
    End Sub
End Class

From the above videos.xml file, this code would result in:

<?xml version="1.0" encoding="utf-8"?>
<videos FileDesc="Personal Video Collection">
  <video ISBN="0-7888-1623-3">
    <title Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video>
    <title WrittenBy="Charlie Peter">Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Mins</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

To support attribute addition, the XmlDocument class is equipped with the CreateAttribute() method, which is overloaded in three versions. The first version of this method has the following syntax:

Public Function CreateAttribute(name As String) As XmlAttribute

This method expects the name of the attribute as argument. If it succeeds, this method produces an XmlAttribute object. To add the new attribute to an element, you can call the XmlElement.SetAttributeNote() method. This method is overloaded in two versions. One of the versions uses the following syntax:

Public Overridable Function SetAttributeNode(newAttr As XmlAttribute) _
		As XmlAttribute

This method expects an XmlAttribute object. Here is an example that looks for a particular video in a collection and adds an ISBN attribute to it:

Private Sub btnDocument_Click(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) _
                              Handles btnDocument.Click
    Dim Filename As String = "videos.xml"
    Dim DocumentElement As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        ' Open the XML file
        DocumentElement.Load(Filename)

        ' Create a new attribute
        Dim ISBNAttribute As XmlAttribute = DocumentElement.CreateAttribute("ISBN")
        ISBNAttribute.Value = "0-7907-3900-3"

        ' Get a list of elements whose names are Video
        Dim ListOfVideos As XmlNodeList = _
		DocumentElement.GetElementsByTagName("video")
        ' Since we will look for a specific video, get the list of all titles
        Dim ListOfTitles As XmlNodeList = _
		DocumentElement.GetElementsByTagName("title")

        ' Visit each title
        For i As Integer = 0 To ListOfTitles.Count - 1
            ' Look for a video whose title is "Her Alibi"
            If ListOfTitles(i).InnerText.Equals("Her Alibi") Then
                ' Once you find that video, add the new attribute to it
                CType(ListOfVideos(i), XmlElement).SetAttributeNode(ISBNAttribute)
            End If
        Next

        DocumentElement.Save("videos.xml")
    End If
End Sub

From the above Videos.xml file, this code would result in:

<?xml version="1.0" encoding="utf-8"?>
<videos FileDesc="Personal Video Collection">
  <video ISBN="0-7888-1623-3">
    <title Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <actors>
    </actors>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video ISBN="0-7907-3900-3">
    <title WrittenBy="Charlie Peter">Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Mins</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

Once an attribute has been created, to identify the element it belongs to, you can access its XmlAttribute.OwnerElement property. This property produces an XmlElement value.

If an element has an attribute you do not want or that you do not need anymore, you can delete that attribute. You have various options, two are available through the XmlElement class.

The attributes of an XmlElement object are considered stored in an indexed list with the most left attribute at index 0, the second from left at index 1, and so on. Based on this, to remove an attribute by locating it based on its index, you can call the XmlElement.RemoveAttributeAt() method. Its syntax is:

Public Overridable Function RemoveAttributeAt(i As Integer) As XmlNode

When calling this method, if an attribute exists at position i, it would be deleted and the method would return it. If there is no attribute at that index, the method does not do anything and it returns 0.

Using the XmlElement.RemoveAtributeAt() method to delete an attribute can be uncertain because you would not know whether there is an attribute at the specified position. An alternative is to specify the name of the attribute you want to delete. To support this, the XmlElement class is equipped with the RemoveAttribute() method, which is overloaded with two versions. One of the versions of this method uses the following syntax:

Public Overridable Sub RemoveAttribute(name As String)

This method expects as argument the name of the attribute to remove.

Another technique you can use consists of defining an XmlAttribute object and submitting it to its XmlElement parent to delete. To do this, you can call the RemoveAttributeNode() method of the XmlElement object. Its syntax is:

Public Overridable Function RemoveAttributeNode ( _
	oldAttr As XmlAttribute) As XmlAttribute

When calling this method, pass the attribute object as argument. If the attribute exists, it would be removed and the method would return the deleted attribute. If the attribute doesn't exist, nothing would happen.

So far, we have used only one attribute per element. Fortunately, you can create as many attributes as you judge necessary in an element. To do this, type the name of each attribute, assign it a double-quoted string and separate the attribute from the next with an empty space. Here is an example of an element with different attributes:

<video ISBN="0-7888-1623-3" ScreenRatio="Standard" SoundtrackAvailable="True" />

As mentioned already and as you should always remember, attributes belong to an element. To support them, the attributes of an element are stored in the Attributes property of the XmlElement class. The XmlElement.Attributes property is based on a class called XmlAttributeCollection. The XmlAttributeCollection class has the following syntax:

Public NotInheritable Class XmlAttributeCollection _
	Inherits XmlNamedNodeMap _
	Implements ICollection, IEnumerable

To know the number of attributes in an element, you can use the XmlNamedNodeMap.Count property.

Whether using its index or name, after accessing an attribute, you can manipulate it as you see fit. For example, you can change or delete it using the same techniques we saw to perform on an individual attribute. Consider the following XML document:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video ISBN="0-7888-1623-3">
    <title Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video">
    <title>Godzilla</title>
    <director>Roland Emmerich</director>
    <length>139 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video ISBN="0-7907-3900-3">
    <title WrittenBy="Charlie Peter">Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Mins</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

As mentioned already, the attributes are stored as a list. Because you have complete access to this list and the positions of its attributes, when creating or adding a new attribute, you can specify the position the new attribute should have in the collection. To create an attribute as the first in an element, you can call the XmlAttributeCollection.Prepend() method. Its syntax is:

Public Function Prepend(node As XmlAttribute) As XmlAttribute

Here is an  example:

Private Sub btnDocument_Click(ByVal sender As System.Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnDocument.Click
    Dim Filename As String = "videos.xml"
    Dim DocumentElement As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        ' Open the XML file
        DocumentElement.Load(Filename)

        ' Create a new attribute
        Dim ISBNAttribute As XmlAttribute = DocumentElement.CreateAttribute("ISBN")
        ISBNAttribute.Value = "0-7907-3900-3"

        ' Get a list of elements whose names are Video
        Dim ListOfVideos As XmlNodeList = _
		DocumentElement.GetElementsByTagName("video")
        ' Since we will look for a specific video, get the list of all titles
        Dim ListOfTitles As XmlNodeList = _
		DocumentElement.GetElementsByTagName("title")

        ' Visit each title
        For i As Integer = 0 To ListOfTitles.Count - 1
            ' Look for a video whose title is "Godzilla"
            If ListOfTitles(i).InnerText.Equals("Godzilla") Then
                ' Once you find that video, "prepend" the new attribute to it
                ListOfVideos(i).Attributes.Prepend(ISBNAttribute)
            End If
        Next

        DocumentElement.Save("videos.xml")
    End If
End Sub

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video ISBN="0-7888-1623-3">
    <title Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video ISBN="0-7907-3900-3">
    <title>Godzilla</title>
    <director>Roland Emmerich</director>
    <length>139 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video ISBN="0-7907-3900-3">
    <title WrittenBy="Charlie Peter">Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Mins</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

Notice that once again we used only one attribute. Image an element of your document has many attributes:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video ISBN="0-7888-1623-3">
    <title Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video ISBN="0-7907-3900-3" widescreen="true">
    <title>Godzilla</title>
    <director>Roland Emmerich</director>
    <length>139 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video ISBN="0-7907-3900-3">
    <title WrittenBy="Charlie Peter">Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Mins</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

Another technique you can use to create an attribute consists of locating one first. Once you have a referenced attribute, to create a new attribute before it, you can call the XmlAttributeCollection.InsertBefore() method. Its syntax is:

Public Function InsertBefore ( _
	newNode As XmlAttribute, _
	refNode As XmlAttribute _
) As XmlAttribute

Here is an example of calling this method:

Private Sub btnDocument_Click(ByVal sender As System.Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnDocument.Click
    Dim Filename As String = "videos.xml"
    Dim DocumentElement As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        ' Open the XML file
        DocumentElement.Load(Filename)

        ' Create a new attribute
        Dim SystemAttribute As XmlAttribute = _
		DocumentElement.CreateAttribute("System")
        SystemAttribute.Value = "NTSC"

        ' Get a list of elements whose names are Video
        Dim ListOfVideos As XmlNodeList = _
			DocumentElement.GetElementsByTagName("video")
        ' Since we will look for a specific video, get the list of all titles
        Dim ListOfTitles As XmlNodeList = _
		DocumentElement.GetElementsByTagName("title")

        ' Visit each title
        For i As Integer = 0 To ListOfTitles.Count - 1
            ' Look for a video whose title is "Her Alibi"
            If ListOfTitles(i).InnerText.Equals("Godzilla") Then
                ' Define the attribute that will be used as referenced point
                Dim WidescreenAttribute As XmlAttribute = _
			ListOfVideos(i).Attributes("widescreen")
                ' Once you find that video, add the new attribute to it
                ListOfVideos(i).Attributes.InsertBefore(SystemAttribute, _
			WidescreenAttribute)
            End If
        Next

        DocumentElement.Save("videos.xml")
    End If
End Sub

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video ISBN="0-7888-1623-3">
    <title Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video ISBN="0-7907-3900-3" System="NTSC" widescreen="true">
    <title>Godzilla</title>
    <director>Roland Emmerich</director>
    <length>139 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video ISBN="0-7907-3900-3">
    <title WrittenBy="Charlie Peter">Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Mins</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

To add a new attribute after the current one, you can call the XmlAttributeCollection.InsertAfter() method. Its syntax is:

public virtual XmlAttribute InsertAfter(XmlAttribute newNode,
					XmlAttribute refNode)

Here is an example:

Private Sub btnDocument_Click(ByVal sender As System.Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnDocument.Click
    Dim Filename As String = "videos.xml"
    Dim DocumentElement As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        ' Open the XML file
        DocumentElement.Load(Filename)

        ' Create a new attribute
        Dim YearAttribute As XmlAttribute = _
		DocumentElement.CreateAttribute("yearreleased")
        YearAttribute.Value = "1998"

        ' Get a list of elements whose names are Video
        Dim ListOfVideos As XmlNodeList = _
		DocumentElement.GetElementsByTagName("video")
        ' Since we will look for a specific video, get the list of all titles
        Dim ListOfTitles As XmlNodeList = _
		DocumentElement.GetElementsByTagName("title")

        ' Visit each title
        For i As Integer = 0 To ListOfTitles.Count - 1
            ' Look for a video whose title is "Her Alibi"
            If ListOfTitles(i).InnerText.Equals("Godzilla") Then
                ' Define the attribute that will be used as referenced point
                Dim ISBNAttribute As XmlAttribute = _
			ListOfVideos(i).Attributes("ISBN")
                ' Once you find that video, add the new attribute to it
                ListOfVideos(i).Attributes.InsertAfter(YearAttribute, _
							ISBNAttribute)
            End If
        Next

        DocumentElement.Save("videos.xml")
    End If
End Sub

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video ISBN="0-7888-1623-3">
    <title Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video ISBN="0-7907-3900-3" yearreleased="1998" System="NTSC" widescreen="true">
    <title>Godzilla</title>
    <director>Roland Emmerich</director>
    <length>139 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video ISBN="0-7907-3900-3">
    <title WrittenBy="Charlie Peter">Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Mins</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

To add an attribute at the end of the list of attributes of an element, you can call the XmlAttributeCollection.Append() method. Its syntax is:

public virtual XmlAttribute Append(XmlAttribute node) 

Consider the following document:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video ISBN="0-7888-1623-3">
    <title Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video ISBN="0-7907-3900-3" yearreleased="1998" System="NTSC" widescreen="true">
    <title>Godzilla</title>
    <director>Roland Emmerich</director>
    <length>139 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video ISBN="0-7907-3900-3" closedcaption="true">
    <title WrittenBy="Charlie Peter">Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Mins</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

Here is an example of calling the XmlAttributeCollection.Append() method:

Private Sub btnDocument_Click(ByVal sender As System.Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnDocument.Click
    Dim Filename As String = "videos.xml"
    Dim DocumentElement As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        ' Open the XML file
        DocumentElement.Load(Filename)

        ' Create a new attribute
        Dim ProducedByAttribute As XmlAttribute = _
		DocumentElement.CreateAttribute("producedby")
        ProducedByAttribute.Value = "Keith Barish"

        ' Get a list of elements whose names are Video
        Dim ListOfVideos As XmlNodeList = _
		DocumentElement.GetElementsByTagName("video")
        ' Since we will look for a specific video, get the list of all titles
        Dim ListOfTitles As XmlNodeList = _
		DocumentElement.GetElementsByTagName("title")

            ' Visit each title
            For i As Integer = 0 To ListOfTitles.Count - 1
                ' Look for a video whose title is "Her Alibi"
                If ListOfTitles(i).InnerText.Equals("Her Alibi") Then
                    ' Once you find that video, add the new attribute to it
                    ListOfVideos(i).Attributes.Append(ProducedByAttribute)
                End If
            Next

            DocumentElement.Save("videos.xml")
        End If
End Sub

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video ISBN="0-7888-1623-3">
    <title Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video ISBN="0-7907-3900-3" yearreleased="1998" System="NTSC" widescreen="true">
    <title>Godzilla</title>
    <director>Roland Emmerich</director>
    <length>139 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video ISBN="0-7907-3900-3" closedcaption="true" producedby="Keith Barish">
    <title WrittenBy="Charlie Peter">Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Mins</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

To access an attribute by its position in the collection, you can use the XmlNamedNodeMap.Item() method. The XmlAttributeCollection class is equipped with an ItemOf indexed property. This property is overloaded in three versions. The first version has the following syntax:

Public ReadOnly Property ItemOf(i As Integer) As XmlAttribute

This property allows you to access an attribute by considering that the attributes are stored in an array. The first or most left attribute has an index of 0; the second attribute from left (of course without counting the name of the element) has an index of 1, and so on.

It can be difficult and sometimes unpredictable, in some scenarios, to access an attribute by its index because you must know exactly where each attribute is positioned. Consider the following version of our Videos.xml XML file:

<?xml version="1.0" encoding="utf-8" ?>
<videos FileDesc="Personal Video Collection">
    <video ISBN="0-7888-1623-3"
	   ScreenRatio="Standard"
	   SoundtrackAvailable="True">
        <title StoryBy="Marty Kaplan and Jonathan Reynold"
	       Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
        <director>Jonathan Lynn</director>
        <actors></actors>
        <length>112 Minutes</length>
        <format>DVD</format>
        <rating>R</rating>
    </video>
    <video ISBN="0-7907-3900-3">
        <title Screenplay="Charlie Peter">Her Alibi</title>
        <director>Bruce Beresford</director>
        <length>94 Mins</length>
        <format>DVD</format>
        <rating>PG-13</rating>
    </video>
</videos>

In the first video, the name of the screenplay writer is stored at index 1. In the second video, the name of the screenplay writer is stored at index 0. In this case, it may not be a good item to use the index to locate an attribute. Fortunately, the second version of the overloaded XmlAttributeCollection.ItemOf() property has the following syntax:

Public ReadOnly Property ItemOf(name As String) As XmlAttribute

With this version, you can explicitly specify the name of the attribute that you want.

Using the list of attributes of an element, you can delete one or all attributes of an element. Since the attributes are stored in a collection, you can locate the undesired attribute by its index and then delete it. To do this, you can call the XmlAttributeCollection.RemoveAt() method. Its syntax is:

public virtual XmlAttribute RemoveAt(int i)

This method expects the index of the attribute that needs to be removed. Consider the following document:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video ISBN="0-7888-1623-3">
    <title Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video ISBN="0-7907-3900-3" yearreleased="1998" System="NTSC" widescreen="true">
    <title>Godzilla</title>
    <director>Roland Emmerich</director>
    <length>139 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video ISBN="0-7907-3900-3" closedcaption="true" producedby="Keith Barish">
    <title WrittenBy="Charlie Peter">Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Mins</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

Here is an example of deleting an attribute by calling the XmlAttributeCollection.RemoveAt() method:

Private Sub btnDocument_Click(ByVal sender As System.Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnDocument.Click
    Dim Filename As String = "videos.xml"
    Dim DocumentElement As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        ' Open the XML file
        DocumentElement.Load(Filename)

        ' Get a list of elements whose names are Video
        Dim ListOfVideos As XmlNodeList = _
		DocumentElement.GetElementsByTagName("video")
        ' Since we will look for a specific video, get the list of all titles
        Dim ListOfTitles As XmlNodeList = _
		DocumentElement.GetElementsByTagName("title")

        ' Visit each title
        For i As Integer = 0 To ListOfTitles.Count - 1
            ' Look for a video whose title is "Her Alibi"
            If ListOfTitles(i).InnerText.Equals("Godzilla") Then
                ' Once you find that video, add the new attribute to it
                ListOfVideos(i).Attributes.RemoveAt(1)
            End If
        Next

        DocumentElement.Save("videos.xml")
    End If
End Sub

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video ISBN="0-7888-1623-3">
    <title Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video ISBN="0-7907-3900-3" System="NTSC" widescreen="true">
    <title>Godzilla</title>
    <director>Roland Emmerich</director>
    <length>139 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video ISBN="0-7907-3900-3" closedcaption="true" producedby="Keith Barish">
    <title WrittenBy="Charlie Peter">Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Mins</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

As mentioned for the XmlAttributeCollection.ItemOf indexed property, to efficiently use this RemoveAt() method, you should know the exact index of the attribute, otherwise, you may access and therefore delete the wrong attribute. An alternative is to explicitly identify the attribute you want to delete. To do this, you can call the XmlAttributeCollection.Remove() method. Its syntax is:

Public Function Remove(node As XmlAttribute) As XmlAttribute

This method takes as attribute the XmlAttribute identification of the attribute you want to remove. Here is an example of calling it:

Private Sub btnDocument_Click(ByVal sender As System.Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnDocument.Click
    Dim Filename As String = "videos.xml"
    Dim DocumentElement As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        ' Open the XML file
        DocumentElement.Load(Filename)

        ' Get a list of elements whose names are Video
        Dim ListOfVideos As XmlNodeList = _
		DocumentElement.GetElementsByTagName("video")
        ' Since we will look for a specific video, get the list of all titles
        Dim ListOfTitles As XmlNodeList = _
		DocumentElement.GetElementsByTagName("title")

        ' Visit each title
        For i As Integer = 0 To ListOfTitles.Count - 1
            ' Look for a video whose title is "Her Alibi"
            If ListOfTitles(i).InnerText.Equals("Her Alibi") Then
                ' Define the attribute that should be deleted
                Dim CCAttribute As XmlAttribute = _
			ListOfVideos(i).Attributes("closedcaption")
                ' If that attribute exists, delete it
                ListOfVideos(i).Attributes.Remove(CCAttribute)
            End If
        Next

        DocumentElement.Save("videos.xml")
    End If
End Sub

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video ISBN="0-7888-1623-3">
    <title Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video ISBN="0-7907-3900-3" System="NTSC" widescreen="true">
    <title>Godzilla</title>
    <director>Roland Emmerich</director>
    <length>139 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video ISBN="0-7907-3900-3" producedby="Keith Barish">
    <title WrittenBy="Charlie Peter">Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Mins</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

To delete all attributes of an element, you can call the XmlAttributeCollection.RemoveAll() method. Its syntax is:

Public Sub RemoveAll

This method would simply remove all attributes that belong to an XmlElement object. Here is an example of calling it:

Private Sub btnDocument_Click(ByVal sender As System.Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles btnDocument.Click
    Dim Filename As String = "videos.xml"
    Dim DocumentElement As XmlDocument = New XmlDocument

    If File.Exists(Filename) Then
        ' Open the XML file
        DocumentElement.Load(Filename)

        ' Get a list of elements whose names are Video
        Dim ListOfVideos As XmlNodeList = _
		DocumentElement.GetElementsByTagName("video")
        ' Since we will look for a specific video, get the list of all titles
        Dim ListOfTitles As XmlNodeList = _
		DocumentElement.GetElementsByTagName("title")

        ' Visit each title
        For i As Integer = 0 To ListOfTitles.Count - 1
            ' Look for a video whose title is "Her Alibi"
            If ListOfTitles(i).InnerText.Equals("Godzilla") Then
                ' Delete all attributes of the title of this video element
                ListOfVideos(i).Attributes.RemoveAll()
            End If
        Next

        DocumentElement.Save("videos.xml")
    End If
End Sub

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video ISBN="0-7888-1623-3">
    <title Screenplay="Marty Kaplan">The Distinguished Gentleman</title>
    <director>Jonathan Lynn</director>
    <length>112 Minutes</length>
    <format>DVD</format>
    <rating>R</rating>
  </video>
  <video>
    <title>Godzilla</title>
    <director>Roland Emmerich</director>
    <length>139 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video ISBN="0-7907-3900-3" producedby="Keith Barish">
    <title WrittenBy="Charlie Peter">Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Mins</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>