Overlay({Key key, List<OverlayEntry> initialEntries: const [] })

Creates an overlay.

The initial entries will be inserted into the overlay when its associated OverlayState is initialized.

Rather than creating an overlay, consider using the overlay that has already been created by the WidgetsApp or the MaterialApp for this application.

Source 

Overlay({
  Key key,
  this.initialEntries: const <OverlayEntry>[]
}) : super(key: key) {
  assert(initialEntries != null);
}