อยากทราบเรื่อง Code vb2008 เรื่องอักษรที่เรากำหนดไม่ให้พิมพ์ textBox ช่วยที งงมาก

If e.KeyChar = Chr(13) Then
  txtEmB.Enabled = True
  txtEmB.Select()
ElseIf e.KeyChar = Chr(64) Then
  txtEmA.Text = txtEmA.Text.Replace("@", String.Empty)
  txtEmB.Enabled = True
  txtEmB.Select()
End If

Private Sub txtEmA_KeyPress(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles txtEmA.KeyPress
        
        If e.KeyChar = Chr(13) Then
            txtEmB.Enabled = True
            txtEmB.Select()
        ElseIf e.KeyChar = Chr(64) Then
            
            txtEmA.Text = txtEmA.Text.Replace("@", String.Empty)
            txtEmB.Enabled = True
            txtEmB.Select()

        End If


        If (e.KeyChar = Chr(8)) And (txtEmA.TextLength = 1) Then
            txtEmA.Select()
            txtEmB.Text = ""
            txtPhA.Text = ""
            txtPhB.Text = ""
            txtPhC.Text = ""
            txtFname.Enabled = True
            txtSname.Enabled = True
            txtP.Enabled = True
            txtPs.Enabled = True
            txtAdd.Enabled = True
            dtpSd.Enabled = True
            dtpBd.Enabled = True
            txtPhA.Enabled = False
            txtEmA.Enabled = True
            txtEmB.Enabled = False
            txtPhA.Enabled = False
            txtPhB.Enabled = False
            txtPhC.Enabled = False
            btnOk.Enabled = False
            txtEmA.Select()

        End If
    End Sub