HOWTO: Keep an MDI Window Always on Top
ID: Q108315
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The information in this article applies to:
-
Microsoft Win32 Software Development Kit (SDK)
-
Microsoft Windows Software Development Kit (SDK) 3.1
-
Microsoft Windows 2000
SUMMARY
When creating a multiple document interface (MDI) window, there are no
styles available to have the new window stay on top of the other MDI
windows. Alternatively, two methods are available to achieve this
functionality:
- Process the WM_WINDOWPOSCHANGED message and call SetWindowPos() to
change the Z-order of the window.
- Install a timer for the MDI windows and reset the Z-order of the window
when processing the WM_TIMER message.
MORE INFORMATION
MDICREATESTRUCT has the field "style", which can be set with the styles for
the new MDI window. Extended styles, such as WS_EX_TOPMOST, are not
available in MDI windows. This field of MDICREATESTRUCT is passed to
CreateWindowEx() in the dwStyle parameter. The dwExStyle field is set to
0L. The two methods shown below cannot be used at the same time in the same
application.
Method 1: Process the WM_WINDOWPOSCHANGED message and call SetWindowPos()
to change the Z-order of the window.
Sample Code
LRESULT CALLBACK MdiWndProc (HWND hWnd, UINT message, WPARAM wParam,
LPARAM lParam)
{
static HWND hWndAlwaysOnTop = 0;
switch (message)
{
case WM_CREATE :
if (!hWndAlwaysOnTop)
{
SetWindowText (hWnd, "Always On Top Window");
hWndAlwaysOnTop = hWnd;
}
break;
case WM_WINDOWPOSCHANGED :
if (hWndAlwaysOnTop)
{
WINDOWPOS FAR* pWP = (WINDOWPOS FAR*)lParam;
if (pWP->hwnd != hWndAlwaysOnTop)
SetWindowPos (hWndAlwaysOnTop, HWND_TOP, 0, 0, 0, 0,
SWP_NOACTIVATE | SWP_NOMOVE | SWP_NOSIZE);
}
break;
//
// Other Messages to process here.
//
case WM_CLOSE :
if (hWndAlwaysOnTop == hWnd)
hWndAlwaysOnTop = NULL;
default :
return DefMDIChildProc (hWnd, message, wParam, lParam);
}
return 0L;
}
Method 2: Install a timer for the MDI windows and reset the Z-order of
the window when processing the WM_TIMER message.
Sample Code
LRESULT CALLBACK MdiWndProc (HWND hWnd, UINT message, WPARAM wParam,
LPARAM lParam)
{
static HWND hWndAlwaysOnTop = 0;
switch (message)
{
case WM_CREATE :
SetTimer (hWnd, 1, 200, NULL);
if (!hWndAlwaysOnTop)
{
SetWindowText (hWnd, "Always On Top Window");
hWndAlwaysOnTop = hWnd;
}
break;
case WM_TIMER :
if (hWndAlwaysOnTop)
{
SetWindowPos (hWndAlwaysOnTop, HWND_TOP, 0, 0, 0, 0,
SWP_NOACTIVATE | SWP_NOMOVE | SWP_NOSIZE);
}
break;
case WM_DESTROY:
KillTimer (hWnd, 1) ;
break;
//
// Other Messages to process here.
//
case WM_CLOSE :
if (hWndAlwaysOnTop == hWnd)
hWndAlwaysOnTop = NULL;
default :
return DefMDIChildProc (hWnd, message, wParam, lParam);
}
return 0L;
}
For additional information on changing the Z-order of child pop-up windows,
please see the following article(s) in the Microsoft Knowledge Base:
Q66943
Determining the Topmost Pop-Up Window
Additional query words:
Keywords : kbcode kbMDI kbNTOS kbWinOS2000 kbSDKWin32 kbGrpUser kbWinOS kbWndw
Version : WINDOWS:3.1
Platform : WINDOWS
Issue type : kbhowto