颤振：文档快照不会返回所有值

Question

我已经在我的距离函数中打印了totalTime，它会产生所有DocumentSnapshot值，这些值来自于我在函数中创建的计算出的距离变量：

Performing hot restart...
Syncing files to device iPhone 11 Pro Max...
Restarted application in 1,761ms.
flutter: 5.631018616945024
flutter: 2.6736733762697478
flutter: 0.6686528422968158
flutter: 1.7422156404871896
flutter: 9.861003284651066

但是在构建方法的ListView.builder的etaText中打印的结果仅返回9.861003284651066（最终的DocumentSnapshot结果）。当我打印出“时间”（在距离函数中等于“ totalTime”）时，它将返回：

flutter: 9.861003284651066
flutter: 9.861003284651066
flutter: 9.861003284651066
flutter: 9.861003284651066
flutter: 9.861003284651066

如果任何人都可以在这里解释我在做什么错，我将不胜感激！谢谢。

import 'dart:async';
import 'dart:math';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';

import 'package:geolocator/geolocator.dart';
import 'package:cloud_firestore/cloud_firestore.dart';

import 'package:myApp/Cards/Store Card.dart';


class StoreList extends StatefulWidget {

  @override
  _StoreListState createState() => _StoreListState();
}


class _StoreListState extends State<StoreList> {


  StreamSubscription<QuerySnapshot> subscription;

  List storeList;

  final CollectionReference collectionReference = Firestore.instance.collection('stores');

  Geolocator geolocator = Geolocator();

  bool sort = true;

  double time;


  Future getLocation() async {
    var currentLocation;
    try {
      currentLocation = await geolocator.getCurrentPosition(
          desiredAccuracy: LocationAccuracy.medium);
    } catch (e) {
      currentLocation = null;
    }
    return currentLocation;
  }


   double calculateDistance(lat1, lon1, lat2, lon2){
    var p = 0.017453292519943295;
    var c = cos;
    var a = 0.5 - c((lat2 - lat1) * p)/2 +
        c(lat1 * p) * c(lat2 * p) *
            (1 - c((lon2 - lon1) * p))/2;
    return 12742 * asin(sqrt(a));
  }


   double distance(Position position, DocumentSnapshot snapshot) {

    final double myPositionLat = position.latitude;
    final double myPositionLong = position.longitude;
    final double lat = snapshot.data['latitude'];
    final double long = snapshot.data['longitude'];

    double totalTime = calculateDistance(myPositionLat, myPositionLong, lat, long) / 8 * 5 * 60 / 35;

    if(totalTime >= 40){
    return totalTime;
  } else setState(() {
    time = totalTime;
    });
      print(totalTime);
    return totalTime;
  }


   void sortDistance(){
    subscription = collectionReference.snapshots().listen((data) async {

      final location = await getLocation();
      final documents = data.documents.where((snapshot) => distance(location, snapshot) <= 40).toList();

//      documents.sort((a, b) {
//        final distanceA = distance(location, a);
//        final distanceB = distance(location, b);
//        return distanceA.compareTo(distanceB);
//      });

      setState(()  {
        storeList = documents;
      });
    });
  }




  @override
  void initState() {
    super.initState();
    sortDistance();
  }



  @override
  void dispose() {
    subscription?.cancel();
    super.dispose();
  }



  @override
  Widget build(BuildContext context) {

    return storeList != null ?

      ListView.builder(

          itemCount: storeList.length,
          itemBuilder: (context, index) {

            print(time);

            String imgPath = storeList[index].data['image'];
            String storeTextPath = storeList[index].data['name'];
            String locationNamePath = storeList[index].data['location'];

            return StoreCard(
              etaText: time,
              locationText: locationNamePath,
              storeText: storeTextPath,
              assetImage: Image.network(imgPath),

              function: (){},
            );
          })

        : Center(child: CircularProgressIndicator());
  }
}