A null reference exception could result at run time

Question

User-152935344 posted

I get a warning message that reads " Variable 'cust' is used before it has been assigned a value. A null reference exception could result at run time.", but it occurs in my vb file "Northwind.vb with the following code:

Public Class Northwind

    Private cust As BizObjects1.Customer

    Private Sub frmCustomer_Load( _
    ByVal sender As System.Object, _
    ByVal e As System.EventArgs) _
    Handles MyBase.Load

        'Load the list of customers
        Dim custList As New BizObjects1.CustomerList
        cbCustomers.DataSource = _
         custList.GetCustomerList.Tables(0)
        cbCustomers.DisplayMember = "CompanyName"
        cbCustomers.ValueMember = "CustomerID"

        cbCustomers.SelectedIndex = -1

        UpdateView()
        Status("Select a customer from list.")
    End Sub

    Private Sub Status(ByVal sMessage As String)
        sbStatus.Text = sMessage
    End Sub

    Private Sub ReadCustomer(ByVal bReload As Boolean)
        Dim cust As BizObjects1.Customer

        If bReload Or cust Is Nothing Then
            cust = New BizObjects1.Customer( _
            cbCustomers.SelectedItem("CustomerID"))
        End If

        lblCustomerID.Text = cust.CustomerID
        txtCustomerName.Text = cust.CompanyName
        txtContactName.Text = cust.ContactName
        txtContactTitle.Text = cust.ContactTitle
        txtAddress.Text = cust.Address
        txtCity.Text = cust.City
        txtRegion.Text = cust.Region
        txtPostalCode.Text = cust.PostalCode
        txtCountry.Text = cust.Country
        txtPhone.Text = cust.Phone
        txtFax.Text = cust.Fax

        Status("")

    End Sub
    Private Sub UpdateView()
        If cbCustomers.SelectedIndex > -1 _
        AndAlso Len(cbCustomers.SelectedItem("CustomerID")) _
        > 0 Then
            cbCustomers.Visible = True
        Else
            cbCustomers.Visible = False

        End If

    End Sub




    Private Sub cmdSaveChanges_click( _
    ByVal sender As System.Object, _
    ByVal e As System.EventArgs) _
    Handles cmdSaveChanges.Click
        Dim cust As New BizObjects1.Customer(lblCustomerID.Text)

        cust.CompanyName = txtCustomerName.Text
        cust.ContactName = txtContactName.Text
        cust.ContactTitle = txtContactTitle.Text
        cust.Address = txtAddress.Text
        cust.City = txtCity.Text
        cust.Region = txtRegion.Text
        cust.PostalCode = txtPostalCode.Text
        cust.Country = txtCountry.Text
        cust.Phone = txtPhone.Text
        cust.Fax = txtFax.Text

        Dim iRows As Int32 = cust.UpdateCustomer
        Select Case iRows
            Case -1
                Status("No customers updated. There were no data " _
                & "changes to make.")
            Case 0
                Status("No customers updated. An error may have " _
                & "occurred.")
            Case 1
                Status("No customers updated one customer record.")
            Case Else
                Status("updated " & iRows.ToString _
                & " customers. This may indicate data " _
                & "corruption since only one customer was " _
                & "targeted for update.")
        End Select

    End Sub

    Private Sub cmdDiscardChanges_Click( _
    ByVal sender As System.Object, _
    ByVal e As System.EventArgs) _
    Handles cmdDiscardChanges.Click
        If Len(cbCustomers.SelectedItem("CustomerID")) > 0 Then
            'Ignore this if there is no customer selected
            ReadCustomer(False)
        End If
    End Sub

    Private Sub cbCustomers_selectedindexchanged( _
    ByVal sender As System.Object, _
    ByVal e As System.EventArgs) _
    Handles cbCustomers.SelectedIndexChanged
        If cbCustomers.SelectedIndex > -1 _
        AndAlso Len(cbCustomers.SelectedItem("CustomerID")) _
        > 0 Then
            ReadCustomer(True)
            Status("Loaded the customer: " _
            & cbCustomers.SelectedItem("CompanyName") & ".")
        Else
            cust = Nothing
            Status("Select a customer from list.")
        End If

        UpdateView()

    End Sub

End Class

Answer 1

User-573138384 posted

I see duplicate variables in your code. You already defined a private variable cust at class level.

Private cust As BizObjects1.Customer

You need not declare cust again in methods. You can use same class level variable here.

Remove this

Dim cust As BizObjects1.Customer

Change this

change

Dim cust As New BizObjects1.Customer(lblCustomerID.Text)

to

cust = New BizObjects1.Customer(lblCustomerID.Text)

Answer 2

User-152935344 posted

Thank you fayaz_3e!!  The error is now removed.