سبب تكرار رسالة التنبيه - نسخة قابلة للطباعة

كود :
' استدعاء درجـات مواد الدور التكميلي 

    Dim messageShown As Boolean = False

    Private Sub Student_Courses()

        DataGridView1.DataSource = Nothing

        DataGridView1.Rows.Clear()

        DataGridView1.Refresh()

        ' استدع الدرجـات حسب الفصل والقسم الدراسي التابع له وحسب رقم الامتحـان

        Try

            Dim arrListQuery As New ArrayList

            For i As Integer = 0 To Form_main.ListBoxClas.Items.Count - 1

                If Form_main.ListBoxClas.GetSelected(i) Then

                    arrListQuery.Add( _

                        "SELECT TBL_Students.StudentID, TBL_Students.StudentName, TBL_Students.ClassID,TBL_Students.ClassroomID " & _

                        ", TBL_Final1.SemesterID as [رقم الامتحــان]" & _

                        ", TBL_Final1.on" & CombCourses.SelectedIndex + 1 & " as [أعمـال] " & _

                        ", TBL_Final1.to" & CombCourses.SelectedIndex + 1 & " as [امتحـان] " & _

                        ", TBL_Final1.tr" & CombCourses.SelectedIndex + 1 & " as [دور ثان] " & _

                        "FROM TBL_Final1 RIGHT JOIN TBL_Students ON TBL_Final1.StudentID=TBL_Students.StudentID " & _

                        "Where TBL_Final1.ClassID=" & CInt(i + 1).ToString() & " and TBL_Final1.ClassroomID=" & Combroom.SelectedIndex + 1 & " and TBL_Final1.SemesterID=2" & " and TBL_Final1.tr" & CombCourses.SelectedIndex + 1 & " < 50" & " and TBL_Final1.result LIKE 'دور ثان" & "' ")

                End If

            Next

            Dim da As OleDb.OleDbDataAdapter = New OleDbDataAdapter(Nothing, Con)

            Dim ds As New DataSet

            For i As Integer = 0 To arrListQuery.Count - 1

                If Not IsNothing(arrListQuery(i)) Then

                    da.SelectCommand.CommandText = arrListQuery(i).ToString

                    da.Fill(ds, "Student")

                End If

            Next



            If ds.Tables("Student").Rows.Count > 0 Then

                DataGridView1.DataSource = ds.Tables("Student")

                FillDataGrid()

                ' بعد تحميل البيانات، نمر على الصفوف لتحديث الأعمدة5 و 6 و7 و8

                For Each row As DataGridViewRow In DataGridView1.Rows

                    If Not row.IsNewRow Then

                        ' العمود 5

                        If row.Cells(5).Value Is Nothing OrElse IsNullOrWhiteSpace(row.Cells(5).Value.ToString()) OrElse row.Cells(5).Value.ToString() = "0" Then

                            row.Cells(5).Value = 0

                        End If

                        ' العمود 6

                        If row.Cells(6).Value Is Nothing OrElse IsNullOrWhiteSpace(row.Cells(6).Value.ToString()) OrElse row.Cells(6).Value.ToString() = "0" Then

                            row.Cells(6).Value = 0

                        End If

                        ' العمود 7

                        If row.Cells(7).Value Is Nothing OrElse IsNullOrWhiteSpace(row.Cells(7).Value.ToString()) OrElse row.Cells(7).Value.ToString() = "0" Then

                            row.Cells(7).Value = 0

                        End If

                    End If

                Next

                Me.Texttotal.Text = " درجات مـادة" & " " & Me.CombCourses.Text & " - لـ " & Form_main.ListBoxClas.Text & " " & ""

                messageShown = False



            Else

                'If Not messageShown Then

                MessageBox.Show("عفـــواً ... لا يوجــد طلبــة لهم دور ثان   ", "تنبيــه", MessageBoxButtons.OK, MessageBoxIcon.Information)

                messageShown = True

            End If

            End If



        Catch ex As Exception

            ' MessageBox.Show("حدث خطأ أثناء تحميل البيانات: " & ex.Message, "خطأ", MessageBoxButtons.OK, MessageBoxIcon.Error)

        End Try



    End Sub