VB .net Object Reference Error

I'll give that a shot first thing in the morning...

I did as suggested and still get the error.  See new code below.  my error message is now dimArgs - System.NullReference.....  So it appears that it is happening on the following line:

Dim img as New Bitmap(TW.Image)

Imports Priore.Controls
Imports System.Runtime.InteropServices
Imports System.IO
Imports System.Collections
Imports System
Imports System.Xml 
Public Class Form1 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Me.Hide() 
        Dim xDoc As New XmlDocument
        xDoc.Load("config.xml")
        Dim strObject = "none"
        Try
            Dim DPI As XmlNodeList = xDoc.GetElementsByTagName("dpi")
            strObject = "DPI"
            Dim colourType As XmlNodeList = xDoc.GetElementsByTagName("colourType")
            strObject = "colourType"
            Dim showIF As XmlNodeList = xDoc.GetElementsByTagName("showInterface")
            strObject = "showIF"
            Dim showPR As XmlNodeList = xDoc.GetElementsByTagName("showProgress")
            strObject = "showPR"
            Dim vDPI As Short = CShort(DPI(0).InnerText)
            strObject = "vDPI"
            Dim vColourType As Twain.TWAIN_CLASS_COLOURTYPE
            strObject = "vColourType"
            Select Case colourType(0).InnerText
                Case "twBW"
                    vColourType = Twain.TWAIN_CLASS_COLOURTYPE.twBW
                Case "twGrey"
                    vColourType = Twain.TWAIN_CLASS_COLOURTYPE.twGREY
                Case "twRGB"
                    vColourType = Twain.TWAIN_CLASS_COLOURTYPE.twRGB
            End Select
            Dim vShowIF As Boolean = CBool(showIF(0).InnerText)
            strObject = "vShowIF"
            Dim vShowPR As Boolean = CBool(showPR(0).InnerText)
            strObject = "vShowPR"
            Dim TW As Twain
            strObject = "dimTW"
            TW = New Twain(Me.Handle)
            strObject = "newTW"
            TW.Resolution = vDPI
            strObject = "setRes"
            TW.ColorType = vColourType
            strObject = "setColour"
            TW.ShowInterface = vShowIF
            strObject = "setIF"
            TW.ShowProgress = vShowPR
            strObject = "setPR"
            TW.StartScan()
            strObject = "StartScan"
            Dim args() As String = Environment.GetCommandLineArgs
            strObject = "dimArgs"
            Dim img As New Bitmap(TW.Image)
            strObject = "copyImage"
            TW.Dispose()
            strObject = "disposeTW"
            Dim saveLoc As String
            saveLoc = args(1) + "-" + DateTime.Now.Year.ToString + DateTime.Now.Month.ToString + DateTime.Now.Day.ToString + DateTime.Now.Hour.ToString + DateTime.Now.Minute.ToString + DateTime.Now.Second.ToString + ".jpg"
            img.Save(saveLoc, Drawing.Imaging.ImageFormat.Jpeg)
            img.Dispose()
        Catch ex As Exception
            MessageBox.Show(strObject & " - " & ex.ToString)
        End Try
        'End
    End Sub
End Class

                                              

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Looks like TW.Image is nothing.

Let's try this:  Change Me.Handle to Process.handle

Me.Handle returns the Handle of the Form you are in.  While Process.Handle returns the Handle attribute of the entire process

See if that works.

Right, but for some reason:

TW.Resolution  = vDPI
TW.ColorType = vColourType
TW.ShowInterface = vShowIF
TW.ShowProgress = vShowPR
TW.StartScan()

The above returns the error that is described.  However, if I change it so that instead of getting the values from the variable and assign them directly like below:

TW.Resolution  = 300
TW.ColorType = twGREY
TW.ShowInterface = false
TW.ShowProgress = true
TW.StartScan()

The above there now works correctly.

In a nutshell, if I hard code the settings, the software will correctly scan and save the image.  However, if I try and make those values dynamic, or read in from a config file, it generates the error.  I placed break points at each of the above assignments and it does in fact get, and assign the correct values.  So that's where I am confused.

When I try to change Me.Handle to Process.Handle, it will not compile and says Error      1      Reference to a non-shared member requires an object reference.      C:\Users\Scott\documents\visual studio 10\Projects\scan\scan\Form1.vb      43      28      scan

Bah!  Send an example of the XML document you are using.

Here's the XML file.

<?xml version="1.0" encoding="utf-8"?>
<settings>
	<dpi>300</dpi>
	<colourType>twGREY</colourType>
	<showInterface>false</showInterface>
	<showProgress>true</showProgress>
</settings>

                                              

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Change this :

Dim DPI As XmlNodeList = xDoc.GetElementsByTagName("dpi")
Dim colourType As XmlNodeList = xDoc.GetElementsByTagName("colourType")
Dim showIF As XmlNodeList = xDoc.GetElementsByTagName("showInterface")
Dim showPR As XmlNodeList = xDoc.GetElementsByTagName("showProgress")

To This:

Dim DPI As string =  xDoc.ChildNodes(0).ChildNodes(0).ChildNodes("dpi").InnerText()
Dim colourType As String = xDoc.ChildNodes(0).ChildNodes(0).ChildNodes("colourType").InnerText()
Dim showIF As String= xDoc.ChildNodes(0).ChildNodes(0).ChildNodes("showInterface").InnerText()
Dim showPR As string = xDoc.ChildNodes(0).ChildNodes(0).ChildNodes("showProgress") .InnerText()

Oops!  Also

 Dim vDPI As Short = CShort(DPI)
            Dim vColourType As Twain.TWAIN_CLASS_COLOURTYPE
            Select Case colourType
                Case "twBW"
                    vColourType = Twain.TWAIN_CLASS_COLOURTYPE.twBW
                Case "twGrey"
                    vColourType = Twain.TWAIN_CLASS_COLOURTYPE.twGREY
                Case "twRGB"
                    vColourType = Twain.TWAIN_CLASS_COLOURTYPE.twRGB
            End Select
            Dim vShowIF As Boolean = CBool(showIF)
            strObject = "vShowIF"
            Dim vShowPR As Boolean = CBool(showPR)

Now it fails as soon as it tries to read the first XML node...

Hmmm....
Maybe I went too far....
Dim DPI As string =  xDoc.ChildNodes(0).ChildNodes("dpi").InnerText()
Dim colourType As String = xDoc.ChildNodes(0).ChildNodes("colourType").InnerText()
Dim showIF As String= xDoc.ChildNodes(0).ChildNodes("showInterface").InnerText()
Dim showPR As string = xDoc.ChildNodes(0).ChildNodes("showProgress") .InnerText()

There is no need of changing the xml code as the asker has mentioned already that the settings are being assigned correctly when he steps through the code.

any ideas?

Apparantly, I think you're pulling the wrong xml nodes.  Try this instead...

        Dim DPI As String = xDoc.ChildNodes(1).ChildNodes(0).InnerText()
        Dim colourType As String = xDoc.ChildNodes(1).ChildNodes(1).InnerText()
        Dim showIF As String = xDoc.ChildNodes(1).ChildNodes(2).InnerText()
        Dim showPR As String = xDoc.ChildNodes(1).ChildNodes(3).InnerText()


Dim vDPI As Short = CShort(DPI)
            Dim vColourType As Twain.TWAIN_CLASS_COLOURTYPE
            Select Case colourType
                Case "twBW"
                    vColourType = Twain.TWAIN_CLASS_COLOURTYPE.twBW
                Case "twGrey"
                    vColourType = Twain.TWAIN_CLASS_COLOURTYPE.twGREY
                Case "twRGB"
                    vColourType = Twain.TWAIN_CLASS_COLOURTYPE.twRGB
            End Select
            Dim vShowIF As Boolean = CBool(showIF)
            strObject = "vShowIF"
            Dim vShowPR As Boolean = CBool(showPR)

If I add a breakpoint on line 35 (in the original code posted with the question), and I examine the values for each of the 4 variables, they are in fact correct, and of the correct type.  The data is being pulled in from the XML file, and is being pulled in and converted correctly without making any changes to the XML parsing part of the code.

I also do not simply want to reference the elements by index in case the order gets changed around in the file.  With it referenced by name the order of elements in the file does not matter, only the name of the tags encompassing them.

OK, lets then example each variable before they get dumped into being made an image.  I truly believe that a value is not "pushed" correctly, if you know what I mean.

 TW.Resolution = vDPI
            TW.ColorType = vColourType
            TW.ShowInterface = vShowIF
            TW.ShowProgress = vShowPR
msgbox("TWR:" & TW.Resolution.ToString)
msgbox("TWC:" &   TW.ColorType .ToString)
msgbox("TWSI:" &  TW.ShowInterface.ToString)
msgbox("TWSP:" &  TW.Progress.ToString)

Checking that now...  I'll let you know what happens.

When adding messagebox.show(TW.Resolution.ToString) and the others, The message boxes all showed the correct values.  However, same error message still arises.

So, to recap.  You put static values into your variables for scanning....

TW.Resolution  = 300
TW.ColorType = twGREY
TW.ShowInterface = false
TW.ShowProgress = true
TW.StartScan()

and everything works fine, every time.  But if you push variable values into the same functions, it cops out?  And from the message boxes, they all hold the same values necessary to function and are the same datatype that is required?  That is one freaky problem.  :(  I've looked over your code, and while I think I'm a knowledgable guy, I'm not really seeing the flaw that would be a show stopper.  

I'm going to throw a crazy suggestion here.  Move the code out of the form_load and make a new button.  Put the code into the button1_click function to see if that changes things.  Sometimes for no expectant reason,  that works.  

no change

This may also help, may not...

When I have the values hard coded, and the application reaches the point in the code where it is to begin scanning (TW.StartScan()), you can hear the scanner start up, and then it scans.  When the values are assigned in dynamically, you hear the scanner start up as it did with them statically set, however, it never scans after that.

I don't know if the program is feeding the scanner some variable that is causing it to seize up or what.  Like you, I too am stumped as the variables that it is feeding it are the correct type and value.

Essentially, what is happening is that the program is starting the scanner, but the scanner never completes and sends the program back an image, thus the object reference error.  changed the code to read as below, and when I did that, the program would hang (so no more error) right after the scanner initialized, and CPU usage spike to 100% (because of the while loop).

Dim myInt As Integer
myInt = -1
myInt = TW.StartScan()
While myInt <> 0 
End While
Dim img As New Bitmap(TW.Image)

                                              

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Awesome!  Feels good doesn't it?