[VB.NET]密碼框顯示程式探討與其簡易的保護之道

<DllImport("user32.dll", SetLastError:=True, CharSet:=CharSet.Auto)> _

Private Shared Function PostMessage(ByVal hWnd As IntPtr, ByVal Msg As UInteger, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As Boolean End Function

Const EM_SETPASSWORDCHAR = &HCC

Private Sub TargetSelectedControl1_TargetSelected(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TargetSelectedControl1.TargetSelected
    Dim hWnd As IntPtr = WindowFromPoint(MousePosition)
    PostMessage(hWnd, EM_SETPASSWORDCHAR, 0, 0)
End Sub</pre></div>

Const WM_SETTEXT As Integer = &amp;HC
Const WM_GETTEXT As Integer = &amp;HD
Const EM_SETPASSWORDCHAR = &amp;HCC

Sub New()
    With Me
        .Multiline = False
        .UseSystemPasswordChar = True
    End With
End Sub

Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)
    If m.Msg = WM_SETTEXT OrElse m.Msg = WM_GETTEXT OrElse m.Msg = EM_SETPASSWORDCHAR Then
        Return
    End If
    MyBase.WndProc(m)
End Sub

End Class