VB NET TextBox Validation

Public Class Form1
    ' to get this example to work, you will need 5 TextBoxes and one buton (leave with default names) on a form
    ' set the Enable property of the button to False, otherwise you wont see it working

    Public Sub New()

        ' This call is required by the designer.
        InitializeComponent()

        ' set the Tag value for each textbox (this is the power of 2)
        ' it is the mask that is added/subtracted to a total (mask) if there text is text in the textbox or not
        TextBox1.Tag = 1
        TextBox2.Tag = 2
        TextBox3.Tag = 4
        TextBox4.Tag = 8
        TextBox5.Tag = 16
        'TextBox6.Tag = 32
        'TextBox7.Tag = 64
        'etc

    End Sub

    Dim mask As Integer

    Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles TextBox1.TextChanged, TextBox2.TextChanged, TextBox3.TextChanged, TextBox4.TextChanged, TextBox5.TextChanged, TextBox6.TextChanged
        ' OK this uses bit masking to validate that there is text in the textbox...
        ' it might seem like a lot of touble to go to but it works well.

' OK so what we are doing in the next few lines of code is 'Anding' the value of 'mask'
' with the tag value of the current textbox
' this will tell us if we have previously verified this textbox and confirmed that it contained text
' now, (because the user has modified the text in this textbox) we have to verify that it still contains
' some text, if not then we subtract the tag value from  mask, if it does then we leave the value of mask  alone…
' example
'mask value of 20 and’ed with tag 4 = 4 (we have previously verified textbox 3)
'mask value of 20 and’ed with tag 16 = 16 (we have previously verified textbox text 5)
'mask value of 20 and’ed with tag 1 = 0 (we have NOT previously verified textbox text 1)

        If (mask And DirectCast(sender, System.Windows.Forms.TextBox).Tag) = DirectCast(sender, System.Windows.Forms.TextBox).Tag Then ' Mask already added
            If DirectCast(sender, System.Windows.Forms.TextBox).Text = String.Empty Then ' if there is no text in this textbox
                mask -= DirectCast(sender, System.Windows.Forms.TextBox).Tag ' subtract the mask
            End If
        ElseIf DirectCast(sender, System.Windows.Forms.TextBox).Text <> String.Empty Then ' mask is not added
            mask += DirectCast(sender, System.Windows.Forms.TextBox).Tag
        End If

        Button1.Enabled = mask = 31 ' for 6 textboxes set this value to 63 for 7 textboxes set it to 127 and so on
    End Sub

End Class