KeyPress 跟KeyDown

KeyPress 和KeyDown
下面是一个combobox的keydown事件和一个keypress事件，我想问下，这代码到底是表达的什么意思 
 Private Sub cboDevId_KeyDown(ByVal eventSender As System.Object, ByVal eventArgs As System.Windows.Forms.KeyEventArgs) Handles cboDevId.KeyDown
  Dim KeyCode As Short = eventArgs.KeyCode
  Dim Shift As Short = eventArgs.KeyData \ &H10000
  Dim KeyAscii As New Object
  On Error GoTo cboDevId_KeyDownErr
  If KeyAscii <> 8 Then KeyAscii = 0
  Exit Sub

cboDevId_KeyDownErr:
  ShowErrorBox("frmGvApp13.cboDevId_KeyDown")
  End Sub

‘-------------------------------------------------
Private Sub cboDevId_KeyPress(ByVal eventSender As System.Object, ByVal eventArgs As System.Windows.Forms.KeyPressEventArgs) Handles cboDevId.KeyPress
  Dim KeyAscii As Short = Asc(eventArgs.KeyChar)
  On Error GoTo cboDevId_KeyPressErr

  'KeyAscii = 0
  If KeyAscii <> 8 Then KeyAscii = 0
  GoTo EventExitSub

cboDevId_KeyPressErr:
  ShowErrorBox("frmGvApp13.cboDevId_KeyPress")
EventExitSub:
  eventArgs.KeyChar = Chr(KeyAscii)
  If KeyAscii = 0 Then
  eventArgs.Handled = True
  End If
  End Sub

[解决办法]
屏蔽退格键之外的按键