flutter_done_overlay.dart

showOverlay(BuildContext context) {
    if (overlayEntry != null) return;
    OverlayState overlayState = Overlay.of(context);
    overlayEntry = OverlayEntry(builder: (context) {
      return Positioned(
          bottom: MediaQuery.of(context).viewInsets.bottom,
          right: 0.0,
          left: 0.0,
          child: InputDoneView());
    });

    overlayState.insert(overlayEntry);
  }

  removeOverlay() {
    if (overlayEntry != null) {
      overlayEntry.remove();
      overlayEntry = null;
    }
  }