How Can I Achieve 'On Desktop' and 'On Bottom' Window Placement in WPF?

Window Placement Control in WPF: "On Desktop" Option

Rainlendar's ability to place windows "on desktop" allows them to behave as bottomMost windows. This is not a built-in feature of WPF, but it can be achieved using Win32 API calls, which require P/Invoke from C#.

Rainlendar's Options:

Rainlendar offers two options for window placement:

• On Desktop: The window becomes a child of the Explorer desktop window, similar to setting the parent using the SetParent API.
• On Bottom: The window remains at the bottom of the Z-order, just above the desktop.

Achieving On Desktop Placement:

To place a WPF window "on desktop," you can use the SetParent API:

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

Setting hWndNewParent to IntPtr.Zero removes the parent and makes the window a desktop child.

Achieving On Bottom Placement:

To keep a window "on bottom," you need to intercept the WM_WINDOWPOSCHANGING message:

protected override void WndProc(ref Message m)
{
    if (m.Msg == (int) WM.WINDOWPOSCHANGING)
    {
        var pos = (WINDOWPOS) Marshal.PtrToStructure(m.LParam, typeof(WINDOWPOS));
        // Check if the window is being promoted to the top
        if ((pos.flags & SWP_NOMOVE) == 0 && (pos.flags & SWP_NOSIZE) == 0)
        {
            pos.hwndInsertAfter = HWND_BOTTOM;
            pos.flags |= SWP_NOACTIVATE;
            Marshal.StructureToPtr(pos, m.LParam, true);
        }
    }
    base.WndProc(ref m);
}

By setting hwndInsertAfter to HWND_BOTTOM and adding the SWP_NOACTIVATE flag, the window will always remain at the bottom and will not activate when clicked.

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