Home > Articles > Web Services > XML

  • Print
  • + Share This
Like this article? We recommend

Like this article? We recommend

Getting Started

Visual Basic.NET provides integrated tools for using XML, schemas, XSL, and other XML-related tools, but there's no need to wait for VB.NET in order to get started. Microsoft XML Core Services (MSXML) version 4.0 gives you the tools you need to load and save XML documents from your Visual Basic 6 application.

Download the most recent version of MSXML at msdn.microsoft.com/xml/default.asp, and install it on your computer. To use MSXML in a Visual Basic 6 program, select the Project menu's References command. Select Microsoft XML, v 4.0 (or whatever the version du jour is), and click OK. Now you're ready to add XML objects to your program.

DOMDocument Class

The DOM (document object model) describes an XML file's hierarchical nature using a corresponding set of programming objects. DOMDocument is the MSXML class that represents an XML document's DOM structure.

The DOMDocument class provides only a few really useful properties and methods. The load method makes the object load an XML file. The loadXML method makes it load XML data from a string. For example, the following code loads a small XML file into the document named xml_document.

Dim xml_document As New DOMDocument

  xml_document.loadXML _
    "<Person>" & vbCrLf & _
    "  <FirstName>Rod</FirstName>" & vbCrLf & _
    "  <LastName>Stephens</LastName>" & vbCrLf & _
    "</Person>"

The DOMDocument's xml property returns the document's XML representation. You can display this value to see what the document looks like. You could also save it into a file, but there's really no need to do that because the DOMDocument object's save method does it automatically.

The object's documentElement property is a node that represents the document's topmost data node. All the other nodes lie within that one. Usually, when you manipulate an XML document's nodes, you will start at this node.

DOMDocument provides several methods for creating new nodes. The createElement method makes a new element node for the document. This is the kind of node you usually want to create. Other node creation methods include createAttribute, createProcessingInstruction, and createTextNode, although I won't say anything about those methods in this article.

IXMLDOMNodeClass

The class IXMLDOMNode represents a node. This class provides a number of properties and methods you can use to search and manipulate the XML document.

The selectSingleNode method searches the node's descendants for a specific node. The language you use to specify the node you want is called XPath, and it's too involved to cover here. Two particularly simple and useful XPath specifications search the node's immediate children and all of its descendants.

If you pass selectSingleNode a child node's name, the method searches the node's children for an exact match. If you pass selectSingleNode the string ".//" followed by a node's name, the method searches the node's descendants for the name.

' Search for a child node named "LastName."
Set last_name_node = address_node.selectSingleNode("LastName")

' Search for any descendant named "LastName."
Set last_name_node = address_node.selectSingleNode(".//LastName")

The following list shows a few of the IXMLDOMNode object's more useful properties:

  • attributes. A collection of the node's attributes.

  • nodeName. Gives the node's tag name.

  • nodeTypeString. Tells you the node's type.

  • ownerDocument. Returns the DOMDocument object containing the node.

  • text. Gives the text contained in the node. If the node contains other nodes, this is the combined text of them all.

  • xml. Gives the node's XML content, as in "<FirstName>Rod</FirstName>".

The childNodes collection contains references to the node's children. To add a new node to this one, you must first create it using one of the DOMDocument object's node-creation methods. Then you add the new node to the parent's childNodes collection. The following code shows a CreateNode subroutine that creates a new node and adds it to a parent node's children using the parent's appendChild method.

' Add a new node to the indicated parent node.
Private Sub CreateNode(ByVal indent As Integer, _
  ByVal parent As IXMLDOMNode, ByVal node_name As String, _
  ByVal node_value As String)
Dim new_node As IXMLDOMNode

  ' Create the new node.
  Set new_node = parent.ownerDocument.createElement(node_name)

  ' Set the node's text value.
  new_node.Text = node_value

  ' Add the node to the parent.
  parent.appendChild new_node
End Sub

SaveValues Program

With these tools, you can build a simple program that uses XML. Program SaveValues, shown in Figure 1, loads and saves values in an XML file. When it starts, the program loads its text boxes using the values in the file Values.xml. When it stops, the program saves its current values into that file.

Figure 1 Program SaveValues loads and saves values in an XML file.

The following code shows a typical Values.xml file.

<Values>
  <FirstName>Rod</FirstName>
  <LastName>Stephens</LastName>
  <Street>1234 Programmer Place</Street>
  <City>Bugsville</City>
  <State>CO</State>
  <Zip>80276</Zip>
</Values>

Listing 1 shows how program SaveValues works. When the program's form loads, the Form_Load event handler calls subroutine LoadValues.

LoadValues creates a DOMDocument object named xml_document, loads the XML file, and uses its selectSingleNode method to find the node named Values. It then uses the GetNodeValue helper function to fetch the values it needs from the descendants of the Values node.

GetNodeValue uses the Values node's selectSingleNode method to find the target node. If the node isn't there, the function returns a default value. If it finds the node, GetNodeValue returns the node's text value. For the data nodes in Values.xml, the text value is simply the text contained in the nodes.

When the program's form unloads, the Form_Unload event handler calls subroutine SaveValues. That routine creates a new DOMDocument object. It creates a new node named Values, and uses the document's appendChild method to add the new node to the document.

SaveValues then calls the CreateNode helper subroutine to save each of the values in the program's text boxes. SaveValues passes a reference to the Values node to CreateNode so that the routine can place the new node in the document's Values section.

After it has created all of the new nodes, SaveValues uses the DOMDocument's save method to save the new XML file.

Note that the new file overwrites the old one. There is no way to change just part of an XML file using the DOMDocument object. You can load the file, make a few small changes, and save the file, but the file is completely overwritten. That is usually not a problem unless some other program may have changed the file in the meantime. In that case, any changes the other program made will be lost when you overwrite the file.

The last piece of the program is the CreateNode subroutine. CreateNode adds a new node with a given value to a parent node. First, the routine uses the parent node's ownerDocument method to get a reference to the DOMDocument object. It uses that object's createElement method to create a new node.

CreateNode then sets the new node's Text property to its desired value, and adds the node to the parent node's children.

Listing 1. Program SaveValues Uses this Code to Load and Save Values in an XML File.

Option Explicit

Private m_AppPath As String

Private Sub Form_Load()
  ' Get the application's startup path.
  m_AppPath = App.Path
  If Right$(m_AppPath, 1) <> "\" Then m_AppPath = m_AppPath & "\"

  ' Load the values.
  LoadValues
End Sub

Private Sub Form_Unload(Cancel As Integer)
  ' Save the current values.
  SaveValues
End Sub

' Load saved values from XML.
Private Sub LoadValues()
Dim xml_document As DOMDocument
Dim values_node As IXMLDOMNode

  ' Load the document.
  Set xml_document = New DOMDocument
  xml_document.Load m_AppPath & "Values.xml"

  ' If the file doesn't exist, then
  ' xml_document.documentElement is Nothing.
  If xml_document.documentElement Is Nothing Then
    ' The file doesn't exist. Do nothing.
    Exit Sub
  End If

  ' Find the Values section.
  Set values_node = xml_document.selectSingleNode("Values")

  ' Read the saved values.
  txtFirstName.Text = GetNodeValue(values_node, "FirstName", "???")
  txtLastName.Text = GetNodeValue(values_node, "LastName", "???")
  txtStreet.Text = GetNodeValue(values_node, "Street", "???")
  txtCity.Text = GetNodeValue(values_node, "City", "???")
  txtState.Text = GetNodeValue(values_node, "State", "???")
  txtZip.Text = GetNodeValue(values_node, "Zip", "???")
End Sub

' Return the node's value.
Private Function GetNodeValue(ByVal start_at_node As IXMLDOMNode, _
  ByVal node_name As String, _
  Optional ByVal default_value As String = "") As String
Dim value_node As IXMLDOMNode

  Set value_node = start_at_node.selectSingleNode(".//" & node_name)
  If value_node Is Nothing Then
    GetNodeValue = default_value
  Else
    GetNodeValue = value_node.Text
  End If
End Function

' Save the current values.
Private Sub SaveValues()
Dim xml_document As DOMDocument
Dim values_node As IXMLDOMNode

  ' Create the XML document.
  Set xml_document = New DOMDocument

  ' Create the Values section node.
  Set values_node = xml_document.createElement("Values")

  ' Add the Values section node to the document.
  xml_document.appendChild values_node

  ' Create nodes for the values inside the
  ' Values section node.
  CreateNode values_node, "FirstName", txtFirstName.Text
  CreateNode values_node, "LastName", txtLastName.Text
  CreateNode values_node, "Street", txtStreet.Text
  CreateNode values_node, "City", txtCity.Text
  CreateNode values_node, "State", txtState.Text
  CreateNode values_node, "Zip", txtZip.Text

  ' Save the XML document.
  xml_document.save m_AppPath & "Values.xml"
End Sub

' Add a new node to the indicated parent node.
Private Sub CreateNode(ByVal parent As IXMLDOMNode, _
  ByVal node_name As String, ByVal node_value As String)
Dim new_node As IXMLDOMNode

  ' Create the new node.
  Set new_node = parent.ownerDocument.createElement(node_name)

  ' Set the node's text value.
  new_node.Text = node_value

  ' Add the node to the parent.
  parent.appendChild new_node
End Sub

Download the SaveValues source code here:

Click here to download program SaveIndented.

SaveValuesIndented Program

Although everyone makes a big deal about how easy XML files are to read, the tools that manipulate them typically ignore the whitespace that makes their structure obvious. The XML parser ignores the indentation and spacing you add to make the file easier to understand.

Unfortunately, the routines that write XML files tend to omit this whitespace, too. Program SaveValues actually creates an XML file that looks like the following with all the data run together on a single line.

<Values><FirstName>Rod</FirstName><LastName>Stephens</LastNa
me><Street>1234 Programmer Place</Street><City>Bugsville</Ci
ty><State>CO</State><Zip>80276</Zip></Values>

VB.NET includes text writer classes that can format XML documents. They aren't trivial to use, but they do work. MSXML doesn't include those text writers, so if you want to save an XML document with a nicely indented format, you need to add the formatting yourself.

In addition to named elements such as the ones shown here, an XML file can contain unnamed text nodes. In fact, the values inside the nodes in this example are already contained in text nodes. For example, if you pick the Values.xml file's structure apart carefully, you will find that the FirstName element contains a text node that holds the text Rod.

You can add your own text nodes between named elements. To give this file a nicely indented structure, you need to add text nodes containing spaces before each node to indent it, and new line characters after each node to make the next node start on the next line. This may seem difficult, but it's really not too hard.

Program SaveValuesIndented uses the code in Listing 2 to save its values. The SaveValues subroutine is almost the same as the previous version. After it creates the Values element, however, this routine adds a text node containing a carriage return and line feed. Putting this text node inside the Values node makes the resulting XML document contain a new line right after the <Values> tag.

SaveValues then calls CreateNode to create the new data nodes. It passes CreateNode a new parameter telling it how far to indent the new nodes.

CreateNode starts by adding a text node containing spaces to the parent node to indent the new node. It then adds the new node to the parent's children, much as the previous version did. It finishes by adding a text node containing a carriage return and line feed to the parent, so whatever follows the new node starts on the next line.

Listing 2. This Code Adds Text Nodes to Indent the Resulting XML Document.

' Save the current values.
Private Sub SaveValues()
Dim xml_document As DOMDocument
Dim values_node As IXMLDOMNode

  ' Create the XML document.
  Set xml_document = New DOMDocument

  ' Create the Values section node.
  Set values_node = xml_document.createElement("Values")

  ' Add a new line.
  values_node.appendChild xml_document.createTextNode(vbCrLf)

  ' Add the Values section node to the document.
  xml_document.appendChild values_node

  ' Create nodes for the values inside the
  ' Values section node.
  CreateNode 4, values_node, "FirstName", txtFirstName.Text
  CreateNode 4, values_node, "LastName", txtLastName.Text
  CreateNode 4, values_node, "Street", txtStreet.Text
  CreateNode 4, values_node, "City", txtCity.Text
  CreateNode 4, values_node, "State", txtState.Text
  CreateNode 4, values_node, "Zip", txtZip.Text

  ' Save the XML document.
  xml_document.save m_AppPath & "Values.xml"
End Sub

' Add a new node to the indicated parent node.
Private Sub CreateNode(ByVal indent As Integer, _
  ByVal parent As IXMLDOMNode, ByVal node_name As String, _
  ByVal node_value As String)
Dim new_node As IXMLDOMNode

  ' Indent.
  parent.appendChild _
    parent.ownerDocument.createTextNode(Space$(indent))

  ' Create the new node.
  Set new_node = parent.ownerDocument.createElement(node_name)

  ' Set the node's text value.
  new_node.Text = node_value

  ' Add the node to the parent.
  parent.appendChild new_node

  ' Add a new line.
  parent.appendChild parent.ownerDocument.createTextNode(vbCrLf)
End Sub

Download the SaveValuesIndented source code here:

Click here to download program
  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020