Flutter-在同一函数中添加'await'时在null上调用VoidCallback

Question

我从一个小部件传递给另一个小部件的VoidCallback，当从第二个小部件调用时，它正常运行，如果我在同一函数中的另一个语句中添加了一个“ await”，它将中断并显示“ null调用错误”

第一个小部件：

  refreshLocalList() async {
    Logger.log("Refrishing list");
    setState(() {appointmentsList=AppointmentsController.getLocalList();});
  }
.
.
.
onTap: (){
    Navigator.of(context).push(MaterialPageRoute(
    builder: (context) => NewAppointment(time:times9to2[index],date: date,cameraId: cameraId.toString(),refreshLocalList: refreshLocalList,showInSnackBar: showInSnackBar,)));
                        },

第二小部件：

    class NewAppointment extends StatefulWidget {
      final String time;
      final String date;
      final String cameraId;
      final VoidCallback refreshLocalList;
      final void Function(String msg) showInSnackBar;
      const NewAppointment({Key key, this.time, this.date,this.cameraId,this.refreshLocalList,this.showInSnackBar}) : super(key: key);
      @override
      _NewAppointmentState createState() => _NewAppointmentState();
    }
class _NewAppointmentState extends State<NewAppointment> {
  Doctor doctor = Doctor();
  _NewAppointmentState();
  Widget build(BuildContext context) {
    return MaterialApp(
.
.
.
child: Text("Submit",
                                ),
                                onPressed: () async {

                                  widget.refreshLocalList();
                                  Appointment newAppointmet = Appointment(doctor_id: DoctorsController.getDoctorIdByName(doctorNameController.text),
                                      date: widget.date,time: widget.time,description: descriptionFieldController.text,camera_id: widget.cameraId);
                                  AppointmentsController.addToLocalList(newAppointmet);
                                  await Queries.createAppointment(doctorNameController.text,widget.date,widget.time,descriptionFieldController.text,widget.cameraId);
                                  Navigator.of(context).pop();
                                  widget.showInSnackBar("Appointment created");
                                }),

回叫是refreshLocalList()

在两种情况下，另一个回调widget.showInSnackBar(String)都可以正常工作。

如果我在Queries.createAppointment之前删除“ await”，则一切正常。

错误：

> I/flutter (14062): full doctors map size 57 E/flutter (14062):
> [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception:
> NoSuchMethodError: The method 'call' was called on null. E/flutter
> (14062): Receiver: null E/flutter (14062): Tried calling: call()

Answer 1

[这是一种理论：可能不需要await就可以工作，因为NewAppointment有机会弹出，并且您的第一个小部件变得可见，因此setState()可以很好地工作。