vb WM_KEYDOWN 参数设置？？？？

Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Declare Function PostMessage Lib "user32" Alias "PostMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Dim cqhwnd As Long
Private Const VK_F1 = &H70
Private Const WM_KEYDOWN = &H100
Private Const WM_KEYUP = &H101
Private Const WM_CLOSE = &H10

Private Sub Command2_Click()
PostMessage cqhwnd, WM_KEYDOWN, VK_A, 0&
PostMessage cqhwnd, WM_KEYUP, VK_A, 0&
End Sub

模拟按下按键。
=================
Private Const VK_F1 = &H70
Private Const WM_KEYDOWN = &H100
Private Const WM_KEYUP = &H101
Private Const WM_CLOSE = &H10
这些什么意思？貌似赋值？
如果我想模拟按Q键，应该赋值为什么？
为什么有些会输出2次？

'函数申明
Private Declare Sub keybd_event Lib "user32" (ByVal bVk As Byte, ByVal Scan As Byte, ByVal dwFlags As Long, ByVal dwExtraInfo As Long)
Const KEYEVENTF_KEYUP = &H2 '释放按键常数

'回车键例子
Private Sub Command1_Click()
Text1.SetFocus
Call keybd_event(13, 0, 0, 0) '按下
Call keybd_event(13, 0, KEYEVENTF_KEYUP, 0) '释放
End Sub

键码
常数 值 描述
vbKeyLButton 1 鼠标左键
vbKeyRButton 2 鼠标右键
vbKeyCancel 3 CANCEL 键
vbKeyMButton 4 鼠标中键
vbKeyBack 8 BACKSPACE 键
vbKeyTab 9 TAB 键
vbKeyClear 12 CLEAR 键
vbKeyReturn 13 ENTER 键
vbKeyShift 16 SHIFT 键
vbKeyControl 17 CTRL 键
vbKeyMenu 18 菜单键
vbKeyPause 19 PAUSE 键
vbKeyCapital 20 CAPS LOCK 键
vbKeyEscape 27 ESC 键
vbKeySpace 32 SPACEBAR 键
vbKeyPageUp 33 PAGEUP 键
vbKeyPageDown 34 PAGEDOWN 键
vbKeyEnd 35 END 键
vbKeyHome 36 HOME 键
vbKeyLeft 37 LEFT ARROW 键