validation code in vb.net

void CharacterValidation(object sender, KeyPressEventArgs e)
       {
           if ((e.KeyChar >= 65 && e.KeyChar <= 90) || (e.KeyChar >= 97 && e.KeyChar <= 122) || e.KeyChar == 32 || e.KeyChar == 8)
           {
               e.Handled = false;
           }
           else
           {
               e.Handled = true;
           }
       }

Public Class MainForm

    Dim charactersAllowed As String = " abcdefghijklmnopqrstuvwxyz"

    Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged
        Dim theText As String = TextBox1.Text
        Dim Letter As String
        Dim SelectionIndex As Integer = TextBox1.SelectionStart
        Dim Change As Integer

        For x As Integer = 0 To TextBox1.Text.Length - 1
            Letter = TextBox1.Text.Substring(x, 1)
            If charactersAllowed.Contains(Letter) = False Then
                theText = theText.Replace(Letter, String.Empty)
                Change = 1
            End If
        Next

        TextBox1.Text = theText
        TextBox1.Select(SelectionIndex - Change, 0)
    End Sub

End Class

Private Sub txtName_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles txtItemCode.KeyPress
        If Asc(e.KeyChar) = Keys.Space Then
            MessageBox.Show("Space not acceptable")
            Exit Sub
        Else
            MessageBox.Show("GOOD")
        End If
    End Sub