showToast method
Toast 关闭 closeToast();
Implementation
Future<ExtendedOverlayEntry?> showToast(Toast toast) async {
if (_toast != null) return _toast;
_toast = showOverlay(toast, autoOff: true);
_toast?.addListener(_toastListener);
final duration =
toast.options?.duration ?? GlobalOptions().toastOptions.duration;
await duration.delayed<dynamic>();
closeToast();
return _toast;
}