I have a form where a person can select how many of a product they want
e.g. 1x2g Syringe, 15x100g jar etc. The code will then display string
output in a label, listing the products that have a quanitity of
greater than 0. This works fine. Now what I wanted to do is that each
time a quanitity text box is changed the form would refresh the string
output. I have done this by calling the procedure (which outputs the
string output) many times for each quantity box's EventChanged event

Here's the procedure which outputs the string output (there are many
more 'gram' variables but they're all similar so i didn't include
them):

Public Sub PackingOutput()
        Dim totalgram As String
        Dim gram2 As String
        Dim gram5 As String
        Dim gram10 As String

        Dim num_txt2g As Integer
        Dim num_txt5g As Integer
        Dim num_txt10g As Integer

        num_txt2g = CInt(txt2g.Text)
        If num_txt2g > 0 Then
            gram2 = num_txt2g & " " & lbl2g.Text & ", "
        End If

        num_txt5g = CInt(txt5g.Text)
        If num_txt5g > 0 Then
            gram5 = num_txt5g & " " & lbl5g.Text & ", "
        End If

        num_txt10g = CInt(txt10g.Text)
        If num_txt10g > 0 Then
            gram10 = num_txt10g & " " & lbl10g.Text & ", "
        End If

        totalgram = gram2 & gram5 & gram10
        lblPackingOutput2.Text = totalgram

And here's an example of the EventChanged events:

    Private Sub txt2g_TextChanged(ByVal sender As System.Object, ByVal
e As System.EventArgs) Handles txt2g.TextChanged
        Call PackingOutput()
    End Sub


    Private Sub txt5g_TextChanged(ByVal sender As System.Object, ByVal
e As System.EventArgs) Handles txt5g.TextChanged
        Call PackingOutput()
    End Sub

    Private Sub txt10g_TextChanged(ByVal sender As System.Object, ByVal
e As System.EventArgs) Handles txt10g.TextChanged
        Call PackingOutput()
    End Sub


The problem is when I just have txt2g_TextChanged it works fine, but if
I have more than one sub calling the same procedure I get "an unhandled
exception of type 'System.InvalidCastException' occurred in
microsoft.visualbasic.dll. Addition information: Cast from string "" to
type 'Integer' is not valid"


Anyone know how to fix?

Hi,

<aziz***@googlemail.com> schrieb im Newsbeitrag
your PackingOutput Sub tries to convert the given texts to integer without
checking if the values in these boxes are numeric. It looks a at least one
text box contained an empty string and the CInt function can't convert this
empty string to an integer...

just a first gues..
Josef

The problem is not really that you are calling the procedure multiple
times.

'Cast from string "" to type 'Integer' is not valid' - means that at
some point one of

    txt2g.text
    txt5g.text
    txt10g.text

contains ""

1) put in some checking in PackingOutput() for empty strings
2) If the only thing that you are doing is calling PackingOutput, then
you can use the one handler for all events

Private Sub HandleTextChanged(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles
     txt2g.TextChanged,
     txt5g.TextChanged,
     txt10g.TextChanged

   PackingOutput()

End Sub

hth,
Alan.

I've checked the text boxes and they all have '0' in them when the
program is initialised. Also before doing anything with them (i.e.
comparison) I always convert the text '0' to an integer using Cint.

Also if I uncomment any of the other ....

        num_txt2g = CInt(txt2g.Text)
        If num_txt2g > 0 Then
            gram2 = num_txt2g & " " & lbl2g.Text & ", "
        End If

.... type of commands, same error comes up. It's only if I have the
first one that the program works.

I'm totally stumped.
I've uploaded the entire form here
http://rapidshare.de/files/15005081/packingoptions.zip.html in case
anyone can help.

Try changing the Debug/Exception settings for 'Common Language Runtime
Exceptions' to Break into the Debugger when an exception is thrown (it
is usually set to Continue).

This will stop the program at the point where the exception occurs and
you can check the values in the various textboxes at that point.

Another option... add a Trace.Writeline() for each textbox value before
calling CInt to see what the value is.

hth,
Alan.

Adding button programatically - NON-FUNCTIONAL!!
Checking for new versions in a setup project
Can a console VB.NET prog return a value to caller?
Garbage collection and callbacks from unmanaged code.
Help with strings.
Error on Graphics CompositingMode.SourceCopy
Numeric Variables
converting from combobox.text to long()
Preventing Explorer Window from Displaying when Pen Drive Inserted
Getting Extended File Properties