Текстовый редактор на VB.Net

Public Class Form1
    Dim a As String
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        SaveToolStripMenuItem.Enabled = False
        SaveFileDialog1.Filter = "Txt files|*.txt|All files|*.*"
        OpenFileDialog1.Filter = "Txt files|*.txt|All files|*.*"
    End Sub
 
    Private Sub OpenToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles OpenToolStripMenuItem.Click
        OpenFileDialog1.RestoreDirectory = True
        OpenFileDialog1.ShowDialog()
        a = OpenFileDialog1.FileName
        If a = "OpenFileDialog1" Then
            MsgBox("Вы ничего не открыли")
        Else
            FileOpen(1, a, OpenMode.Input)
            While Not EOF(1)
                TextBox1.Text = TextBox1.Text + LineInput(1) + Environment.NewLine
            End While
            FileClose(1)
            SaveToolStripMenuItem.Enabled = True
        End If
    End Sub
 
    Private Sub SaveToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles SaveToolStripMenuItem.Click
        If a <> "OpenFileDialog1" Then
            System.IO.File.WriteAllText(a, TextBox1.Text)
        End If
    End Sub
 
    Private Sub SaveAsToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles SaveAsToolStripMenuItem.Click
        SaveFileDialog1.ShowDialog()
        Dim filetosavename As String = SaveFileDialog1.FileName
        System.IO.File.WriteAllText(filetosavename, TextBox1.Text)
    End Sub
End Class