如何使计时器超时而不是取消

Question

我有一个RefreshIndicator，希望将来会回来。该RefreshIndicator进行回调，该回调返回计时器并返回未来。计时器基本上是无限运行的（从某种意义上来说），我希望在其他地方从计时器上调用cancel时将调用超时代码completer.complete();。 但是，当我在计时器上调用timer.cancel时，不会调用lambda completer.complete();。计时器是否具有强制超时机制，或者我有更好的方法来解决此问题？这是我的代码

void getEmployees({bool force=false,String query="",Timer refreshTimer})
    {
services.getEmployees(url:query).then((modelEmployeeCollection col){

            if(refreshTimer!=null) {
                refreshTimer.cancel();
            }

            refreshState(() {
                isBusy = false;
            });
        });
}
 Future<Null> _onRefresh() {
        Completer<Null> completer = new Completer<Null>();
        Timer timer = new Timer(new Duration(seconds: 500), () {
            completer.complete();
        });
        getEmployees(force: true,query: employeeCacheNextPreviousShared,refreshTimer: timer);
        return completer.future;
    }

var refreshListView = new RefreshIndicator(child: emplyeeListView, onRefresh:_onRefresh);