如何使Text文本框的属性只读？

声明：

Private Declare Function SendMessage Lib "user32" Alias _
   "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, _
ByVal wParam As Long, lParam As Any) As Long

Private Const EM_SETREADONLY = &HCF
程序：
Private Sub Form_Load()
    Call SendMessage(Text1.hwnd, EM_SETREADONLY, True, vbNull)
End Sub