Problem of variable that are used before assigned a value

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Hello guys,
I had one error in my code but I don't know exactly how to correct it
Please help me out
my program it display the fellowong message as worning message

Warning 1 Variable 'UserRoles' is used before it has been assigned a value. A null reference exception could result at runtime. C:\Users\DAVID\Pictures\Library Project\Library Project\CuuLIB\CuuLIB\LoginForm2.vb 36 16 CuuLIB

here doing are the following code I m using, thank you

VB

Imports System.Data.OleDb
Imports System.Media
Public Class LoginForm2
   
    Dim path = System.Windows.Forms.Application.StartupPath
    Dim LogOnsound As String
    Dim MyPlayer As New SoundPlayer()

    Private Sub LoginForm2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        LogOnsound = "\LogOn.wav"
    End Sub
    Private Sub OK_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OK.Click
        Dim connection As New OleDbConnection("PROVIDER=Microsoft.ACE.OleDb.12.0;DATA SOURCE = CUULibDB.mdb.accdb;")
        ''Dim command As New OleDbCommand("SELECT [ID] FROM [Staff] WHERE [usernameField] = username AND [passwordField] = password", connection)
        Dim command As New OleDbCommand("SELECT a.ID,a.RoleID FROM Staff a ,Role b WHERE a.usernameField = username AND a.passwordField = password ", connection)
        Dim UserRoles As String
        Dim usernameParam As New OleDbParameter("username", Me.UsernameTextBox.Text)
        Dim passwordParam As New OleDbParameter("password", Me.PasswordTextBox.Text)

        command.Parameters.Add(usernameParam)
        command.Parameters.Add(passwordParam)

        command.Connection.Open()
        Dim reader As OleDbDataReader = command.ExecuteReader()
        If reader.HasRows Then

            Do While reader.Read()
                UserRoles = reader.Item(1)
            Loop

            MessageBox.Show("you are authenticated")
            MyPlayer.SoundLocation = path & LogOnsound
            MyPlayer.Play()
            PasswordTextBox.Text = ""
            Me.Hide()
            If UserRoles = "1" Then
                LibrarySoftForm.Show()
            Else
                cuulibForm.Show()
            End If

        Else
            MessageBox.Show("username and or password are not found")
            PasswordTextBox.Text = ""
        End If

        command.Connection.Close()

    End Sub


    Private Sub Cancel_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Cancel.Click
        Me.Close()
    End Sub

End Class

Posted 11-Aug-13 5:30am

DAVID DUSHIMIMANA

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[no name] 11-Aug-13 11:34am

So simply assign a value and your error will go away, Dim UserRoles As String = String.Empty

DAVID DUSHIMIMANA 11-Aug-13 11:45am

Thank you so much Sir, your help has been work properly

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OriginalGriff · Answer 1 · 2013-08-11T05:53:00

The reason it complains is pretty simple. If I cut down your code a bit it's a clearer:

VB

Private Sub OK_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OK.Click
    Dim UserRoles As String
    Dim reader As OleDbDataReader = command.ExecuteReader()
        Do While reader.Read()
            UserRoles = reader.Item(1)
        Loop
        If UserRoles = "1" Then
            LibrarySoftForm.Show()
        End If
End Sub

The compiler can see a route through your code where UserRoles is never assigned a value before it reaches the If condition - basically, if the reader returns no rows. If your code takes that path at run time, then a null reference exception would be thrown, so it is letting you know before you get a problem in six months time.

Either check for Nothing as well as a specific value, or assign a default value when you define the variable which will "force" it to take the path you want if there are no rows.