How To Acquire Descriptive Information on an XML Error in Visual Basic (252339)


The information in this article applies to:

  • Microsoft XML 2.0
  • Microsoft XML 3.0
  • Microsoft XML 4.0
  • ActiveX Data Objects (ADO) 2.5
  • ActiveX Data Objects (ADO) 2.6
  • ActiveX Data Objects (ADO) 2.7
  • Microsoft Visual Basic Professional Edition for Windows 5.0
  • Microsoft Visual Basic Professional Edition for Windows 6.0
  • Microsoft Visual Basic Enterprise Edition for Windows 5.0
  • Microsoft Visual Basic Enterprise Edition for Windows 6.0
This article was previously published under Q252339

SUMMARY

The XML Object Model provides several ways to handle errors when they occur as a result of the XML document. One of these is the document object's ParseError property, which provides information about problems that may occur in an XML document. This information enables you to handle possible errors and shield users from them. The code sample provided in this article demonstrates the use of some of these properties.

Unicode data is stored as 2 bytes per character, allowing for proper parsing of international language characters and symbols. However, when you save data of this type in ASCII format, errors occur when you try to open and parse the file.

MORE INFORMATION

The following sample utilizes the Customers table in the Microsoft SQL Server Northwind database. Some of the contact names in this table contain international language characters and symbols. The sample creates an ADO recordset by selecting several fields in this table. Subsequently, the data is saved to an XML document using the CreateTextFile method of the FileSystemObject. You can set the last argument of this method to save the file in either Unicode or ASCII format; this argument is optional. If you set the argument to "False" or omit it entirely, the file is created as ASCII.

To see the useful information that can be obtained from the ParseError property, save the data from the Recordset as ASCII. Subsequently, if you try to open the file and parse its data to fill a Visual Basic TreeView control, the error "An Invalid Character Was Found in Text Content" results.
If a newer version of MSXML has been installed in side-by-side mode, you must explicitly use the Globally Unique Identifiers (GUIDs) or ProgIDs for that version to run the sample code. For example, MSXML version 4.0 can only be installed in side-by-side mode. For additional information about the code changes that are required to run the sample code with the MSXML 4.0 parser, click the following article number to view the article in the Microsoft Knowledge Base:

305019 INFO: MSXML 4.0 Specific GUIDs and ProgIds

  1. To run this sample, start a new Visual Basic Standard EXE Project. Form1 is created by default.
  2. From the Project menu, click References, and then select the following items from the References list:

    Microsoft ActiveX Data Objects Library 2.1 or later
    Microsoft XML 1.0 or later
    Microsoft Scripting Runtime*

    *The FileSystemObject Object Model is contained in the Scripting Type Library.

  3. Draw the following controls on Form1 and set their properties as follows: 
    Control            Name                    Caption or Text

Command Button     cmdOpenRS               Open A Recordset
Command Button     cmdSaveRSasXML          Save RS as XML
Command Button     cmdOpenXMLandDisplay    Open XML File and Display
Command Button     cmdExit                 Exit
Text Box           txtErrorInfo            Multi-Line:  True 
                                           ScrollBars:  3-Both
Label              lblErrorInfo            Error Information:
TreeView Control*  tvCustErr
    *The TreeView Control is part of the Windows Common Controls.
  4. From the Project menu, select Components, and then click Windows Common Controls.
  5. From the Project menu, select Add Module. Copy the following code into the Module Code Window that appears:
    Option Explicit
Public cn As New ADODB.Connection
Public rs As New ADODB.Recordset
Public myI As Integer
Public StrTmp As String
Public Errs1 As Errors
Public myFSO As New FileSystemObject
Public mytxtStream As TextStream
Public domdoc As New MSXML.DOMDocument

' To specify a specific version, use a declaration like the following, with the appropriate version in the ProgID:
' Public domdoc As New MSXML2.DOMDocument40
  6. Copy the following code into the General Declarations section of the code window.

    NOTE: Replace your server name, user ID and password information in the connection string.
    Option Explicit

Private Sub cmdOpenRS_Click()

    On Error GoTo AdoError
    
    If cn.State = 1 Then
        cn.Close
        Set cn = Nothing
    End If
    
    If rs.State = 1 Then
        rs.Close
        Set rs = Nothing
    End If
    
    Screen.MousePointer = vbHourglass
    
'   Change your connections string values here:
    cn.Open "driver={SQL Server};Server=YourServer; " & _
             "uid=YourUID;pwd=YourPassword;database=Northwind"    
    With rs
        .CursorLocation = adUseClient
        .CursorType = adOpenKeyset
        .LockType = adLockOptimistic
        .CacheSize = 50
        .Source = "Select CustomerID, " & _
        "CompanyName, ContactName, Region from Customers"
        .ActiveConnection = cn
        .Open
    End With
    
    rs.MoveLast
    rs.MoveFirst
    
    Screen.MousePointer = vbNormal
    
    MsgBox "There are " & rs.RecordCount & " Records in the RS"
    
    Exit Sub

AdoError:

Dim errLoop As Error
Dim strError As String

    myI = 1
    
    StrTmp = StrTmp & vbCrLf & "VB Error # " & Str(Err.Number)
    StrTmp = StrTmp & vbCrLf & "   Generated by " & Err.Source
    StrTmp = StrTmp & vbCrLf & "   Description  " & Err.Description
    
' Display Error Information for each Error object.
    Set Errs1 = cn.Errors
    For Each errLoop In Errs1
        With errLoop
            StrTmp = StrTmp & vbCrLf & "Error #" & myI & ":"
            StrTmp = StrTmp & vbCrLf & "   ADO Error   #" & .Number
            StrTmp = StrTmp & vbCrLf & "   Description  " & .Description
            StrTmp = StrTmp & vbCrLf & "   Source       " & .Source
            myI = myI + 1
        End With
    Next
    
    MsgBox StrTmp

End Sub

Private Sub cmdExit_Click()

    If cn.State = 1 Then
        cn.Close
        Set cn = Nothing
    End If
    
    If rs.State = 1 Then
        rs.Close
        Set rs = Nothing
    End If
    
    Unload Me

End Sub

Private Sub cmdOpenXMLandDisplay_Click()

On Error GoTo MyXMLPerr

'Fill The TreeView with data from the XML Document:

    With domdoc
        .async = False
        .Load App.Path & "\CustErr.xml"
    End With

    If domdoc.readyState = 4 Then
        tvCustErr.Nodes.Clear
        AddNode domdoc.documentElement
    End If
    
    Exit Sub
    
'If an error occurs, display the Source of the error, the line number
'in the XML Document that the error occurred on and the text of the error:

MyXMLPerr:

       txtErrorInfo.Text = domdoc.parseError.reason & vbCrLf & _
                            " Line Number In Document: " & domdoc.parseError.Line & _
                            vbCrLf & domdoc.parseError.srcText

End Sub

Private Sub cmdSaveRSasXML_Click()

   Screen.MousePointer = vbHourglass

'If the file already exists, first Kill it
'and then create it.
'If it does not already exist, simply create it:
   On Error GoTo mdkNoSeeEm
   Const mdkNoSeeEm = 53 'File Not Found
   Kill "Customers.xml"

'Create a Text file using the FileSystemObject:
'For Ascii, last setting is False.  Unicode is True

   Set mytxtStream = myFSO.CreateTextFile(App.Path & "\CustErr.xml", True, False)
   
'To save the file in Unicode format
    'Set mytxtStream = myFSO.CreateTextFile(App.Path & "\CustErr.xml", True, True)

   mytxtStream.WriteLine "<?xml version=""1.0"" standalone=""yes""?>"
   mytxtStream.WriteLine "<Customers>"

   rs.MoveFirst

   Do While Not rs.EOF
        mytxtStream.WriteLine "<Customer>"
        mytxtStream.WriteLine "<CustomerID>" & _
                                rs.Fields("CustomerID") & "</CustomerID>"
        mytxtStream.WriteLine "<CompanyName>" & _
                                rs.Fields("CompanyName") & "</CompanyName>"
        mytxtStream.WriteLine "<ContactName>" & _
                                rs.Fields("ContactName") & "</ContactName>"
        mytxtStream.WriteLine "<Region>" & rs.Fields("Region") & "</Region>"
        mytxtStream.WriteLine "</Customer>"
        rs.MoveNext
   Loop
   rs.MoveFirst

   mytxtStream.WriteLine "</Customers>"

   mytxtStream.Close

   Screen.MousePointer = vbNormal

   Exit Sub

mdkNoSeeEm:
    If Err.Number = mdkNoSeeEm Then
        Resume Next
    End If
       
    Screen.MousePointer = vbNormal

End Sub

Private Sub AddNode(ByRef myNode As IXMLDOMNode, Optional ByRef TreeNode As Node)

Dim tvcusterrNode As Node
Dim tvcusterrNodeList As IXMLDOMNodeList
Dim i As Long
          
    If TreeNode Is Nothing Then
        Set tvcusterrNode = tvCustErr.Nodes.Add
    Else
        Set tvcusterrNode = tvCustErr.Nodes.Add(TreeNode, tvwChild)
    End If
    
    tvcusterrNode.Expanded = True
    tvcusterrNode.Text = myNode.nodeName
    
    If tvcusterrNode.Text = "#text" Then
        tvcusterrNode.Text = myNode.nodeTypedValue
    Else
        tvcusterrNode.Text = "<" & tvcusterrNode.Text & ">"
    End If

    Set tvcusterrNodeList = myNode.childNodes
    For i = 0 To tvcusterrNodeList.length - 1
        AddNode tvcusterrNodeList.Item(i), tvcusterrNode
    Next
End Sub
  7. Run the project.
  8. Click the Open A Recordset command button to open a connection and recordset, which displays the RecordCount property.
  9. Click Save RS as XML to create the XML document file. Note that the last argument of the CreateTextFile is initially set to "False" in order to create the file in ASCII format.
  10. Click Open XML File and Display. If an error occurs, the error information will be displayed in the Error Information text box.
  11. In this scenario, the details on the reason, line, and source text for the error are displayed as follows: 

    An Invalid character was found in text content.
Line Number In Document: 17
<CompanyName>Antonio Moreno Taquer?/CompanyName>

    This message indicates that there is an invalid character in the CompanyName element on line 17 of the XML document. To view the actual data on line 17 of the document object model, open the file with a text editor that is capable of numbering the lines, such as Microsoft Excel. This will show that the actual company name of the data on line 17 contains a special character above the "i" in "Taqueria."
  12. To avoid this error, go into the code window for the Save RS as XML command button (cmdSaveRSasXM). Comment out the line that creates the file with its last argument set to "False".
  13. Uncomment the line that creates the file with its last argument set to "True".
  14. Run the project again. The error described in this article will not occur.
Note, however, that other errors may occur. For example, the error indicating that "White Space is Not Allowed" might occur. This likely indicates that special characters (such as brackets, ampersands, apostrophes, or double quotation marks) exist in the document. XML predefines entity references or escape characters for these.

REFERENCES

For additional information regarding the handling of these characters, click the article number below to view the article in the Microsoft Knowledge Base:

251354 How To Locate and Replace Special Characters in an XML Document with Visual Basic

Modification Type:MinorLast Reviewed:6/29/2004
Keywords:kbDatabase kbhowto KB252339 kbAudDeveloper
©2004 Microsoft Corporation. All rights reserved.