事实上是使用SetWindowPos()来改变z-order，所谓z-order是屏幕一般是以x轴y轴
来表示位置，而以z轴表示前後位置，这便是z-order
bWndInsertAfter的设定值
HWND_BOTTOM Places the window at the bottom of the Z order. If the hwnd
parameter identifies a topmost window, the window loses its
topmost status and is placed at the bottom of all other
windows.
HWND_NOTOPMOST Places the window above all non-topmost windows (that is,
（本文来源于图老师网站，更多请访问http://m.tulaoshi.com/bianchengyuyan/）behind all topmost windows). This flag has no effect if the
window is already a non-topmost window.
HWND_TOP Places the window at the top of the Z order.
HWND_TOPMOST Places the window above all non-topmost windows. The window
maintains its topmost position even when it is deactivated.
wFlag的设值
SWP_DRAWFRAME Draws a frame (defined in the window's class description) around the window.
SWP_FRAMECHANGED Sends a WM_NCCALCSIZE message to the window, even if the window's size is not being changed. If this flag is not specified, WM_NCCALCSIZE is sent only when the window's size is being changed.
SWP_HIDEWINDOW Hides the window.
SWP_NOACTIVATE Does not activate the window. If this flag is not set, the window is activated and moved to the top of either the topmost or non-topmost group (depending on the setting of the hwndInsertAfter parameter).
SWP_NOCOPYBITS Discards the entire contents of the client area. If this flag is not specified, the valid contents of the client area are saved and copied back into the client area after the window is sized or repositioned.
SWP_NOMOVE Retains the current position (ignores the x and y parameters).
SWP_NOSIZE Retains the current size (ignores the cx and cy parameters).
SWP_NOREDRAW Does not redraw changes. If this flag is set, no repainting of any kind occurs. This applies to the client area, the nonclient area (including the title bar and scroll bars), and any part of the parent window uncovered as a result of the
（本文来源于图老师网站，更多请访问http://m.tulaoshi.com/bianchengyuyan/）SWP_NOZORDER Retains the current Z order (ignores the hwndInsertAfter parameter).
SWP_SHOWWINDOW Displays the window.
范例
Const SWP_NOMOVE = &H2Const SWP_NOSIZE = &H1Const FLAG = SWP_NOMOVE Or SWP_NOSIZEConst HWND_TOPMOST = -1Const HWND_NOTOPMOST = -2Const HWND_TOP = 0Const HWND_BOTTOM = 1Private Declare Function SetWindowPos Lib "user32" _ (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 LongPrivate Sub Command1_Click()Call SetWindowPos(Me.hwnd, HWND_TOPMOST, 0, 0, 0, 0, FLAG)End SubPrivate Sub Command2_Click()Call SetWindowPos(Me.hwnd, HWND_NOTOPMOST, 0, 0, 0, 0, FLAG)End Sub
