在QuerySnapshot Flatter Firebase always null中使用ForEach是否有问题

我有以下返回未来列表的代码。我遍历每个文档，获取其纬度和经度，然后计算项目lat/long与当前位置或任何其他位置之间的距离。两个主要问题：

即使数据不为null，itemAddressLat和itemAddressLong也会抛出null，但如果我将这两个求值替换为：

  itemAddressLat =
             double.tryParse(doc.data()[Str.ITEM_LATITUDE].toString()) ??
                 0.00;
         itemAddressLong = double.tryParse(
                 doc.data()[Str.ITEM_LONGITUDE].toString()) ??
             0.00;

零错误；发生异常。NoSuchMethodError（NoSuchMethodError:对null调用了方法“toDouble”。未引发Receiver:null尝试调用：toDouble（）。如果缺少？？0.0，则抛出错误并终止代码。请注意，即使使用null检查，传递的值也不是0.0

控制函数testDistanceBetween（）工作正常，并提供了正确的地址（用以下内容确认：），但主函数-foreach循环将提供累积值

 Future<List> getDistances() async {
 double itemAddressLat = 0.0;
 double itemAddressLong = 0.0;
 await FirebaseFirestore.instance
     .collection(Str.ITEMS)
     .get()
     .then((QuerySnapshot querySnapshot) => {
           querySnapshot.docs.forEach((doc) {//DEBUGGING THIS IT WILL SHOW THE CORRECT LATITUDE AND LONGITUDE AS BUT THE DISTANCE IS NOT CORRECT: 
             itemAddressLat =
                 double.tryParse(doc.data()[Str.ITEM_LATITUDE].toString());
             itemAddressLong =
                 double.tryParse(doc.data()[Str.ITEM_LONGITUDE].toString());
             distance = distanceBetween(itemAddressLat, itemAddressLong,
                 usersCurrentLocationLat, usersCurrentLocationLong);
         //breakpoint at this point will first show distance as null while the coordinates as: -1.2675001, 22.7865, 0.3367397, 32.6650065 (I copied this from the debugger) and pressing continue once, then the distance is: 1114005.0 pressing continue second time, distance is now: 3603715.0 increasing. This is not setting properly - expected: each loop the distance for the once cycle is set.
             distance = distance.roundToDouble();
             distanceList.add(distance);
           })
         });


 return distanceList;
}

void testDistanceBetween() {THIS WORKS
 double distanceInMeters =
     distanceBetween(-1.2675001, 22.7865, 0.3466796, 32.6590033); returns: 1113
 print("TO BE SURE IF THIS WORKS: " + (distanceInMeters / 1000).toString());
}

我使用了下面的另一种方法来计算距离，结果是相同的=distanceBetween不是问题，问题是foreach循环，即guese

另一种距离计算器方法由@提供：

好几天了，我的头都裂了

 double distanceInMeters = distanceBetween(52.2165157, 6.9437819, 52.3546274, 4.8285838);

    double calculateDistance(double lat1, double lng1, double lat2, double lng2) {
    double radEarth = 6.3781 * (pow(10.0, 6.0));
    double phi1 = lat1 * (pi / 180);
    double phi2 = lat2 * (pi / 180);

    double delta1 = (lat2 - lat1) * (pi / 180);
    double delta2 = (lng2 - lng1) * (pi / 180);

    double cal1 = sin(delta1 / 2) * sin(delta1 / 2) +
        (cos(phi1) * cos(phi2) * sin(delta2 / 2) * sin(delta2 / 2));

    double cal2 = 2 * atan2((sqrt(cal1)), (sqrt(1 - cal1)));
    double distance = radEarth * cal2;

    return (distance);
  }