Contoh kode untuk form login di vb.net

#Region "Deklarasi"
    Dim MyConnection As New AccessData.DatabaseConnection
    Dim objConnection As OleDbConnection
    Dim objCommand As OleDbCommand
    Dim objDataAdapter As OleDbDataAdapter
    Dim objdatareader As OleDbDataReader
    Dim strSQL As String
    Dim objDataSet As New DataSet
    Dim objDataTable As New DataTable
    Dim f_utama As New f_utama
#End Region

#Region "Sub"
    Sub login()
        Try
            'Mencari data user berdasarkan NIK yang dimasukkan pada txtuser
            CekUser()
            'tidak boleh mengkosongkan username & password
            If txtuser.Text.Trim() = "" And _
                   txtPassword.Text.Trim() = "" Then
                MsgBox("Masukan Username dan Password", MsgBoxStyle.OKOnly, "POS")
                txtuser.Focus()
            ElseIf txtuser.Text = "" Then
                MsgBox("Masukan Username ", MsgBoxStyle.OKOnly, "POS")
                txtuser.Focus()
            ElseIf txtPassword.Text = "" Then
                MsgBox("Masukan password ", MsgBoxStyle.OKOnly, "POS")
                txtPassword.Focus()
            Else
                'jika username dan password tidak kosong, maka program akan mengecek
                'apakah data yang dicari tersedia pada objDataTable.
                'Jika Tidak (baris data = 0 ) maka akan keluar pesan
                'bahwa username tidak ada
                If objDataTable.Rows.Count <= 0 Then
                    MsgBox("Username tidak ada ", MsgBoxStyle.OKOnly, "POS")
                    txtuser.Focus()
                Else
                    'jika data yang di cari ada, maka program akan mencari password
                    'berdasarkan username (NIK) yang dimasukkan.
                    Find_User()
                    'jika password yang di masukkan salah atau tidak sama
                    ' dengan yang ada pada tabel, maka akan keluar pesan dari program
                    If Password <> Trim(txtPassword.Text) Then
                        MsgBox("Password salah!", MsgBoxStyle.OKOnly, "POS")
                        txtPassword.Focus()
                        Exit Sub
                    Else
                        'Jika benar program akan menampilkan pada form utama
                        Me.ShowInTaskbar = False
                        Me.Close()
                        Me.Dispose()
                        f_utama.ShowDialog()
                        txtuser.Text = ""
                        txtPassword.Text = ""
                    End If
                End If
            End If
        Catch When Err.Number <> 0
            MsgBox("Tidak dapat melakukan proses" _
            & vbCrLf & Err.Description)
            MyConnection.close()
        End Try

    End Sub

    Sub Find_User()
        objCommand = MyConnection.open.CreateCommand
        objCommand.CommandText = ("Select Users.NIK,Users.[Password],Karyawan.[FirstName], Users.RoleID" & _
        " FROM Karyawan INNER JOIN Users ON Karyawan.NIK = Users.NIK where Users.NIK='" & Trim(txtuser.Text) + "' ")
        objdatareader = objCommand.ExecuteReader
        objdatareader.Read()
        Username = objdatareader.Item("NIK")
        Password = objdatareader.Item("Password")
        Nama = objdatareader.Item("FirstName")
        RoleID = objdatareader.Item("RoleID")
        MyConnection.close()
    End Sub

    Sub CekUser()
        objDataTable.Clear()
        strSQL = ("SELECT * FROM [Users] WHERE [NIK] = '" & Trim(txtuser.Text) & "' ")
        objCommand = New OleDbCommand
        objCommand.Connection = MyConnection.open
        objCommand.CommandType = CommandType.Text
        objCommand.CommandText = strSQL
        objDataAdapter = New OleDbDataAdapter(objCommand)
        objDataAdapter.Fill(objDataSet, "MDT_user")
        objDataTable = objDataSet.Tables("MDT_user")
        MyConnection.close()
    End Sub
#End Region


    Private Sub btnBatal_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnBatal.Click
        Dim mYes_No As String = MsgBox("Apakah anda mau keluar dari program ?", vbYesNo, "POS")
        If mYes_No = vbYes Then
            End
        Else
            Exit Sub
        End If
    End Sub

    Private Sub btnLogin_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnLogin.Click
        login()
    End Sub

    Private Sub F_Login_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        MyConnection.close()
    End Sub

    Private Sub txtPassword_KeyUp(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles txtPassword.KeyUp
        If e.KeyCode = Keys.Enter Then
            btnLogin.PerformClick()
        ElseIf e.KeyCode = Keys.Escape Then
            btnBatal.PerformClick()
        End If
    End Sub