XML combo problems

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Guest

am trying to have XML data show results in a combobox (Which works) and
when the combobox has a selection, change the text in a label field.

I am following the video from
http://msdn.microsoft.com/vbasic/atthemovies/dataandxml/default.aspx (reading
XML data) almost step by step (changing to match my xmlfiles, etc)

Here is an example of my XML
<products>
<product>CP-90, T-32</product>
<company>Carwell</company>
<address>Street Address</address>
<city>City</city>
<state>State</state>
<zip>Zip</zip>
</products>

My load function (which works)

Dim xmlFile As String = "..\Products.xml"
Dim xmlDoc As XmlDocument
Private Sub Zadig_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
Dim xmlTr As New XmlTextReader(xmlFile)

While xmlTr.Read
If xmlTr.Name = "product" AndAlso xmlTr.NodeType =
XmlNodeType.Element Then
cmbProducts.Items.Add(xmlTr.ReadString)
End If
End While
xmlTr.Close()

xmlDoc = New XmlDocument
xmlDoc.Load(xmlFile)

End Sub

My selection method
Private Sub cmbProducts_SelectionChangeCommitted(ByVal sender As Object,
ByVal e As System.EventArgs) Handles cmbProducts.SelectionChangeCommitted
DisplayProduct(cmbProducts.SelectedIndex + 1)
End Sub

Here is where the problem begins

Sub DisplayProduct(ByVal position As Integer)
Dim node As XmlNode = xmlDoc.SelectSingleNode( _
"/products/product[" & position & "]")
lblCompany.Text = node.SelectSingleNode("company").InnerText

End Sub

Everything compiles fine but when I run and then select a product I get.
An unhandled exception of type 'System.NullReferenceException' occurred in
Zadig.exe

Additional information: Object reference not set to an instance of an object.

The error says it is on line "lblCompany.Text =
node.SelectSingleNode("company").InnerText" but I have no idea what the real
problem is.

Please advise.

Michael
 
Michael,
Here is an example of my XML
<products>
<product>CP-90, T-32</product>
<company>Carwell</company>
<address>Street Address</address>
<city>City</city>
<state>State</state>
<zip>Zip</zip>
</products>
Click to expand...

You are trying to select child node <company> of node <product>.
But product has no children. That is why you get a NullReferenceException.
I think what you are doing wrong here is the structure of the XML document.
In your example there was no way to associate a <company> or <address> etc.
to a product(other than physichal order in file, but do not rely on that).
I think you should restructure your document in order to look something like
this:
<products>
<!-- Repeat the structure below for each product. -->
<product>
<id>CP-90, T-32</id>
<company>Carwell</company>
<address>Street Address</address>
<city>City</city>
<state>State</state>
<zip>Zip</zip>
</product>

<!-- Next product here-->
</products>

That is a logical hierarchy.
In that example i moved what i think is the product ID into a new <id>
element.

Now you should have no problems with the XPath selection.


--
Regards,
Dennis JD Myrén
Oslo Kodebureau
fremenusul said:
am trying to have XML data show results in a combobox (Which works) and
when the combobox has a selection, change the text in a label field.

I am following the video from
http://msdn.microsoft.com/vbasic/atthemovies/dataandxml/default.aspx
(reading
XML data) almost step by step (changing to match my xmlfiles, etc)

Here is an example of my XML
<products>
<product>CP-90, T-32</product>
<company>Carwell</company>
<address>Street Address</address>
<city>City</city>
<state>State</state>
<zip>Zip</zip>
</products>

My load function (which works)

Dim xmlFile As String = "..\Products.xml"
Dim xmlDoc As XmlDocument
Private Sub Zadig_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
Dim xmlTr As New XmlTextReader(xmlFile)

While xmlTr.Read
If xmlTr.Name = "product" AndAlso xmlTr.NodeType =
XmlNodeType.Element Then
cmbProducts.Items.Add(xmlTr.ReadString)
End If
End While
xmlTr.Close()

xmlDoc = New XmlDocument
xmlDoc.Load(xmlFile)

End Sub

My selection method
Private Sub cmbProducts_SelectionChangeCommitted(ByVal sender As Object,
ByVal e As System.EventArgs) Handles cmbProducts.SelectionChangeCommitted
DisplayProduct(cmbProducts.SelectedIndex + 1)
End Sub

Here is where the problem begins

Sub DisplayProduct(ByVal position As Integer)
Dim node As XmlNode = xmlDoc.SelectSingleNode( _
"/products/product[" & position & "]")
lblCompany.Text = node.SelectSingleNode("company").InnerText

End Sub

Everything compiles fine but when I run and then select a product I get.
An unhandled exception of type 'System.NullReferenceException' occurred in
Zadig.exe

Additional information: Object reference not set to an instance of an
object.

The error says it is on line "lblCompany.Text =
node.SelectSingleNode("company").InnerText" but I have no idea what the
real
problem is.

Please advise.

Michael
Click to expand...
 
ITS WORKS!!!!!

You guys are great!!!!

Dennis Myrén said:
Michael,
Here is an example of my XML
<products>
<product>CP-90, T-32</product>
<company>Carwell</company>
<address>Street Address</address>
<city>City</city>
<state>State</state>
<zip>Zip</zip>
</products>
Click to expand...

You are trying to select child node <company> of node <product>.
But product has no children. That is why you get a NullReferenceException.
I think what you are doing wrong here is the structure of the XML document.
In your example there was no way to associate a <company> or <address> etc.
to a product(other than physichal order in file, but do not rely on that).
I think you should restructure your document in order to look something like
this:
<products>
<!-- Repeat the structure below for each product. -->
<product>
<id>CP-90, T-32</id>
<company>Carwell</company>
<address>Street Address</address>
<city>City</city>
<state>State</state>
<zip>Zip</zip>
</product>

<!-- Next product here-->
</products>

That is a logical hierarchy.
In that example i moved what i think is the product ID into a new <id>
element.

Now you should have no problems with the XPath selection.


--
Regards,
Dennis JD Myrén
Oslo Kodebureau
fremenusul said:
am trying to have XML data show results in a combobox (Which works) and
when the combobox has a selection, change the text in a label field.

I am following the video from
http://msdn.microsoft.com/vbasic/atthemovies/dataandxml/default.aspx
(reading
XML data) almost step by step (changing to match my xmlfiles, etc)

Here is an example of my XML
<products>
<product>CP-90, T-32</product>
<company>Carwell</company>
<address>Street Address</address>
<city>City</city>
<state>State</state>
<zip>Zip</zip>
</products>

My load function (which works)

Dim xmlFile As String = "..\Products.xml"
Dim xmlDoc As XmlDocument
Private Sub Zadig_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
Dim xmlTr As New XmlTextReader(xmlFile)

While xmlTr.Read
If xmlTr.Name = "product" AndAlso xmlTr.NodeType =
XmlNodeType.Element Then
cmbProducts.Items.Add(xmlTr.ReadString)
End If
End While
xmlTr.Close()

xmlDoc = New XmlDocument
xmlDoc.Load(xmlFile)

End Sub

My selection method
Private Sub cmbProducts_SelectionChangeCommitted(ByVal sender As Object,
ByVal e As System.EventArgs) Handles cmbProducts.SelectionChangeCommitted
DisplayProduct(cmbProducts.SelectedIndex + 1)
End Sub

Here is where the problem begins

Sub DisplayProduct(ByVal position As Integer)
Dim node As XmlNode = xmlDoc.SelectSingleNode( _
"/products/product[" & position & "]")
lblCompany.Text = node.SelectSingleNode("company").InnerText

End Sub

Everything compiles fine but when I run and then select a product I get.
An unhandled exception of type 'System.NullReferenceException' occurred in
Zadig.exe

Additional information: Object reference not set to an instance of an
object.

The error says it is on line "lblCompany.Text =
node.SelectSingleNode("company").InnerText" but I have no idea what the
real
problem is.

Please advise.

Michael
Click to expand...
Click to expand...
 
fremenusul.

Did you know that your XML file looks as a datatable, which is a part of a
dataset.

A dataset is much easier to use in combination with a combobox.
Something as
dim ds as new dataset
ds.readxml("mypath")
combobox1.datasource = ds.tables("products")
combobox1.displaymember = "product"
combobox1.valuemember = "company"

Private Sub cmbProducts_SelectionChangeCommitted(ByVal sender As Object,
ByVal e As System.EventArgs) Handles cmbProducts.SelectionChangeCommitted
dim mystring as string = combobox1.selectedvalue
End sub

Just to give you an idea for an alternative

Cor
 
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