asked on

Leave Event Error (System.NullReferenceException: Object reference not set to an instance of an object.)

I'm trying to use a textbox.Leave event and execute a piece of code. The error I get only happens in one situation. Also, I've never had this type of error box display before.

I've included:
1) The error I am getting.
2) Default setup code of a text box I wish to leave and execute code.
3) txtPaymentAmount.Leave function
4) cmboProperty_SelectedIndexChange. The function that is executed prior to the leave event.

If I do not execute the cmboProperty_SelectedIndexChanged code, I can change the text in txtPaymentAmount with no error. If I do click on a record from the dropdown of cmboProperty, I set focus to txtPaymentAmount...and when I change the text value, it errs. The cmbo box function sets the text for several other cmbo boxes and then populates a datagrid by setting .RowFilter.

I am stumped as to what the problem could be. Should I be using Validating/Validated or is using Leave the appropiate event for this function. Once txtPaymentAmount is entered I am updating a field on the datagrid invoices until paymentamount is drawned down to 0 like what is done in Quickbooks.

1)
See the end of this message for details on invoking
just-in-time (JIT) debugging instead of this dialog box.

************** Exception Text **************
System.NullReferenceException: Object reference not set to an instance of an object.
at ASSNHOME.PaymentRegister.txtPaymentAmount_Leave(Object sender, EventArgs e)
at System.Windows.Forms.Control.OnLeave(EventArgs e)
at System.Windows.Forms.Control.NotifyLeave()
at System.Windows.Forms.ContainerControl.UpdateFocusedControl()

2)
'
' txtPaymentAmount
'
Me.txtPaymentAmount.BackColor = System.Drawing.SystemColors.Control
Me.txtPaymentAmount.Font = New System.Drawing.Font("Microsoft Sans Serif", 8.25!, System.Drawing.FontStyle.Regular,
System.Drawing.GraphicsUnit.Point, CType(0, Byte))
Me.txtPaymentAmount.Location = New System.Drawing.Point(545, 50)
Me.txtPaymentAmount.Name = "txtPaymentAmount"
Me.txtPaymentAmount.Size = New System.Drawing.Size(115, 20)
Me.txtPaymentAmount.TabIndex = 201
Me.txtPaymentAmount.Text = ""

3)
Private Sub txtPaymentAmount_Leave(ByVal sender As Object, ByVal e As System.EventArgs) Handles txtPaymentAmount.Leave
If Not IsNumeric(txtPaymentAmount.Text) Then
Beep()
MsgBox("NOT A VALID PAYMENT AMOUNT!!")
txtPaymentAmount.Text = 0
txtPaymentAmount.Focus()
Exit Sub
Else
Dim i As Int32 = 0
Dim xPaymentAmount As Double = txtPaymentAmount.Text
Dim drv As DataRowView
While i <= dvInvoice.Count - 1 And xPaymentAmount > 0
Select Case drv(i)("invoice_balance")
Case Is = xPaymentAmount
drv = dvInvoice(i)
drv.BeginEdit()
drv("payment_amount") = xPaymentAmount
drv.EndEdit()
xPaymentAmount = 0
Case Is < xPaymentAmount
Case Is > xPaymentAmount
End Select
i += 1
End While
End If
End Sub

4)
Private Sub cmboProperty_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmboProperty.SelectedIndexChanged
If Activating Then Exit Sub
If cmboProperty.SelectedIndex > 0 Then
Dim drv As DataRowView = dvProperties(cmboProperty.SelectedIndex)
cmboSubdivision.SelectedValue = drv("subdivision_id").ToString
cmboContact.SelectedValue = drv("contact_id").ToString
cmboStreet.SelectedValue = drv("property_id").ToString
txtPropertyID.Text = drv("property_id").ToString
PopulateInvoices(drv("property_id").ToString, drv("contact_id").ToString)
txtPaymentAmount.Focus()
Else
cmdClearNew_Click(Nothing, Nothing)
End If
Activating = False
End Sub

5)
Private Sub PopulateInvoices(ByVal xPropertyID As Int64, ByVal xContactID As Int64)
dvInvoice.RowFilter = "property_id = " & xPropertyID & " AND contact_id = " & xContactID
End Sub

ASKER CERTIFIED SOLUTION

Bob Learned

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TSFLLC

ASKER

Bob,

The changes worked!

But, what made you make the determination to change from a select case statement to an if statement, and why a single instead of double?
Should I be using Single datatypes for ALL temporary money fields?

After reviewing your code I also just realized that I was trying to dim xPaymentAmount as a double without getting the value of txtPaymentAmount.Text.

Thanks much!

TSFLLC

ASKER

Bob,

I just found a posting where Fernando wrote regarding changing Action Solution Configuration would affect the Breakpoint. That is why my debug was not working. It was set to Release, not Debug. Just the same, I would have had issue with this code.

Thanks!

Bob Learned

Select Case blocks are, IMHO, good for strict case matching (0, 1, 2, 3, ... or "A", "B", "C"). The logic that you had was more of an If...Then statement, and doesn't lend itself very well to a Select Case.

Actually, the internal working data type for floating numbers in the .NET framework is Decimal. You can choose Single, Double, or Decimal interchangeably, as long as you are working with currency and not worried about the accuracy of the floating point. Choosing data type is nitpicking in this case, but if you want to stick with a type, use Decimal.

Bob