VB SendMessage WM_KEYDOWN/WM_KEYUP为何无法发送按键

Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As String) As Long
Private Const WM_CHAR = &H102
Private Const WM_KEYDOWN = &H100
Private Const VK_R = &H52
Private Const WM_KEYUP = &H101

Private Sub Command1_Click()
SendMessage Text1.hwnd, WM_KEYDOWN, 13, 0&
SendMessage Text1.hwnd, WM_KEYUP, 13, 0&
End Sub
点了为何text1里面没有出现回车？

如果使用
SendMessage Text1.hwnd, WM_CHAR, 13, 0&
就会有无数个回车发到text1里面，最终死循环~
有人说吧0改成1就是发送一个，但是无效还是无限回车

请高手回答

PostMessage 可以举例吗？

用 SendMessage 无效 就改用 PostMessage 试试 肯定行的, 原先我就有一个程序也是发送按键消息,用sendmessage怎也不行,后来从网上查了查资料 改用postmessage 就搞定了...

说详细点可以 吗？