实际上Always On Top是借助Windows API的SetWindowPos实现的。 
    1、首先应该把以下声明放再窗体的声明部分： 
    Const SWP_NOSIZE = &H1 
    Const SWP_NOMOVE = &H2 
    Const SWP_NOACTIVATE = &H10 
    Const HWND_TOPMOST = -1 
    Const HWND_NOTOPMOST = -2 
    Const SWP_SHOWWINDOW = &H40 
    Private Declare Function SetWindowPos Lib _ 
     "user32" Alias "SetWindowPos" (ByVal hwnd As Long, _ 
     ByVal hWndInsertAfter As Long, ByVal x As Long, _ 
     ByVal y As Long, ByVal cx As Long, ByVal cy As Long, _ 
     ByVal wFlags As Long) As Long 
    使窗口Always On Top时，可以用下面的语句： 
    SetWindowPos hWnd, HWND_TOPMOST, 0, 0, 0, 0, _ 
     SWP_NOACTIVATE Or SWP_SHOWWINDOW Or SWP_NOMOVE _ 
    Or SWP_NOSIZE 
    使窗口取消Always On Top功能，用下面的语句： 
    SetWindowPos hWnd, HWND_NOTOPMOST, 0, 0, 0, 0, _ 
     SWP_NOACTIVATE Or SWP_SHOWWINDOW Or SWP_NOMOVE _ 
    Or SWP_NOSIZE 
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