Question

How would you put a WinForms form behind desktop icons but in front of the wallpaper? To make the desktop the form’s parent, I use:

    [DllImport("user32.dll", SetLastError = true)]
    static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

    [DllImport("user32.dll", SetLastError = true)]
    static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);

    IntPtr desktopHandle = (IntPtr)FindWindow("Progman", null);
    WallForm wallWindow = new WallForm();//WinForms Form

    ...

    private void SwitchParent()
    {
        wallWindow.Show();
        SetParent(wallWindow.Handle, desktopHandle);
        //wallWindow.SendToBack();
    }

This works, but it puts the form in front of the desktop icons. If I call SendToBack on my form, it disappears, presumably behind the wallpaper. How could I get the form to be between the icons and the desktop background?

Answer 1

I don’t believe that this is possible to do. The desktop window is a single window that renders the desktop image and the icons, so there is no way to insert your window between the desktop image and the icons.

Short of writing a shell replacement that handled the background image and desktop icons differently (a major development task with many hurdles) the only other option I can think of is to hook into the desktop’s events and intercept WM_ERASEBKGND or similar to do your own drawing. (See this question or this question for more info.)

Unfortunately this won’t let you put a WinForm behind the icons, only an image. You’d have to handle a lot of other windows messages to simulate an actual form. It’s a major undertaking regardless.