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Refreshing and Redrawing the Desktop Window

Currently my application needs to draw directly over the entire desktop.  In doing so, I obtain its device context by calling the CWindowDC constructor.  After doing so, I am able to successfully paint directly to the desktop like I need to.  However, when I finish, I need to restore the desktop to its original state (i.e. refresh it - exactly equivalent to what happens if you click on the desktop and press the F5 key).  I have tried many ways of doing this, all without success.  Any insight would be great.  Thanks.
0
mueller
Asked:
mueller
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1 Solution
 
jabaCommented:
HWND hwndDT = GetDesktopWindow();
InvalidareRect(hwndDT, NULL);
UpdateWindow(hwndDT);
Thats all
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muellerAuthor Commented:
Unfortunately, I went down that path prior to posting the question and came up drawing blanks.  Take the following code for example, which gets the desktop window's device context, draws a text string to it, and attempts to clean up the mess afterwards (all in the same manner as above, but as applied to MFC).

-------------------------------------------------------------------------
// get desktop window
CWnd *pWnd = GetDesktopWindow();

// get desktop window's device context
CWindowDC desktopDC( pWnd );

// write some string out to the dc
desktopDC.TextOut( 50, 50, "Hello" );

// attempt to clean up the desktop
pWnd->InvalidateRect( NULL, TRUE );

// update the window
pWnd->UpdateWindow();
-------------------------------------------------------------------------

Again, the code above does not work, and follows your example  in a similar manner (the difference being you call the Win32 API, but no big deal).  Also, when passing through the online Visual C++ 4 documentation the other day looking for info on CWnd::RedrawWindow(), I found an interesting note at the bottom of the "Remarks" section:

When the RedrawWindow member function is used to invalidate part of the desktop window, that window does not receive a WM_PAINT message. To repaint the desktop, an application should use CWnd::ValidateRgn, CWnd::InvalidateRgn, CWnd::UpdateWindow, or ::RedrawWindow.


However, when I followed the advice, I still came up drawing blanks.  If anyone has any insight, I'd be very appreciative. Thanks.
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chensuCommented:
Try this:

::SHChangeNotify(SHCNE_UPDATEDIR, SHCNF_FLUSH, 0, 0);
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chensuCommented:
Maybe the following code is better. I hope it will update the desktop.

// Get the PIDL for the Desktop.
LPITEMIDLIST pidlDesktop;  // PIDL for the Desktop
if (SUCCEEDED(::SHGetSpecialFolderLocation(pWnd->GetSafeHwnd(), CSIDL_DESKTOP, &pidlDesktop)))
{
    // Refresh the Desktop
    ::SHChangeNotify(SHCNE_UPDATEDIR, SHCNF_IDLIST, (DWORD)pidlDesktop, 0);

    // pointer to the shell's IMalloc interface.
    LPMALLOC pMalloc;

    // Get the shell's allocator.
    if (SUCCEEDED(::SHGetMalloc(&pMalloc)))
    {
        // Free the PIDL returned by SHGetSpecialFolderLocation
      pMalloc->Free(pidlDesktop);

        // Release the shell's allocator.
        pMalloc->Release();
    }
}

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muellerAuthor Commented:
Unfortunately the code used to update and refresh the desktop by using the Shell API was not successful.  If anyone has any ideas, it would be great.  Thanks again.
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muellerAuthor Commented:
Adjusted points to 150
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chensuCommented:
The following code does it. (You can use Spy++ to find that the top desktop window is Program Manager window.)

CWnd *pWnd = CWnd::FindWindow("Progman", "Program Manager");
if (pWnd != NULL)
{
    pWnd->ShowWindow(SW_HIDE);
    pWnd->ShowWindow(SW_SHOWNA);
}

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muellerAuthor Commented:
Chensu,

          Thanks for all of the help.  I did use Spy++ earlier to grab the desktop window's class name, but mine came up with
"SysListView32".  I tried the FindWindow method with that class name but always came up blank.  Again, thanks for the help.

                                                 Steve
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chensuCommented:
The "SysListView32" window that you got is the child of the "Program Manager" window that is the top level window. The class name "SysListView32" belongs to the List View control.
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