用GetFocus函数可获得激活窗口(拥有输入焦点的窗口)的句柄
Private Declare Function GetFocus Lib "user32" Alias "GetFocus" () As Long
调用一个窗口的窗口函数,将一条消息发给那个窗口
Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any)