How to sort Windows by z-index?

Question

If I'm enumerating windows in Application.Current.Windows, how can I tell, for any two windows, which one is "closer" (i.e. has greater z-index)?

Or, to say the same in other words, how can I sort those windows by z-index?

Answer 1

Ah this was a really fun one:

[DllImport("user32.dll")]
static extern IntPtr GetActiveWindow();

public static Window ActiveWindow
{
    get
    {
        return HwndSource.FromHwnd(GetActiveWindow()).RootVisual as Window;
    }
}

It will give you the active window in your app (which is usually the foremost).

Answer 2

You cannot get a Window's Z Order information from WPF so you must resort to Win32.

Something like this ought to do the trick:

var topToBottom = SortWindowsTopToBottom(Application.Current.Windows.OfType<Window>());
...

public IEnumerable<Window> SortWindowsTopToBottom(IEnumerable<Window> unsorted)
{
  var byHandle = unsorted.ToDictionary(win =>
    ((HwndSource)PresentationSource.FromVisual(win)).Handle);

  for(IntPtr hWnd = GetTopWindow(IntPtr.Zero); hWnd!=IntPtr.Zero; hWnd = GetNextWindow(hWnd, GW_HWNDNEXT)
    if(byHandle.ContainsKey(hWnd))
      yield return byHandle[hWnd];
}

const uint GW_HWNDNEXT = 2;
[DllImport("User32")] extern IntPtr GetTopWindow(IntPtr hWnd);
[DllImport("User32")] extern IntPtr GetNextWindow(IntPtr hWnd, uint wCmd);

The way this works is:

1. It uses a dictionary to index the given windows by window handle, using the fact that in the Windows implementation of WPF, Window's PresentationSource is always HwndSource.
2. It uses Win32 to scan all unparented windows top to bottom to find the proper order.