GlobalKey<RefreshIndicatorState> refreshIndicatorKey;
  
 showForRefresh() {
    ///显示刷新
    refreshIndicatorKey.currentState.show();
  }

  @override
  Widget build(BuildContext context) {
    refreshIndicatorKey =  new GlobalKey<RefreshIndicatorState>();
    return new RefreshIndicator(
      key: refreshIndicatorKey,
      onRefresh: onRefresh,
      child: new ListView.builder(
        ///·····
      ),
    );
  }