属性 'latitude' 不能无条件访问，因为接收者可以是 'null'。尝试使访问有条件（使用“？”）

Question

我在 Text( "纬度：" + currentPosition.latitude.toString(), ) 这一行。我不知道如何让 currentPosition.latitude not null 帮助我解决这些问题。

它给我这个属性 'latitude' 不能无条件访问因为接收者可以是 'null'。尝试使访问有条件（使用'?.'）或向目标添加空检查（'！'）。错误。

无法无条件访问属性'longitude'，因为接收者可以是'null'。尝试使访问有条件（使用'?.'）或向目标添加空检查（'！'）。错误

import 'package:flutter/material.dart';
import 'package:fluttertoast/fluttertoast.dart';
import 'package:geocoding/geocoding.dart';
import 'package:geolocator/geolocator.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomeApp(),
    );
  }
}

class HomeApp extends StatefulWidget {
  HomeApp({Key? key}) : super(key: key);

  @override
  State<HomeApp> createState() => _HomeAppState();
}

class _HomeAppState extends State<HomeApp> {
  String currentAddress = 'my address';
  Position? currentPosition;
  Future<Position?> _determinePosition() async {
    bool serviceEnabled;
    LocationPermission permission;
    serviceEnabled = await Geolocator.isLocationServiceEnabled();
    if (!serviceEnabled) {
      Fluttertoast.showToast(msg: 'Please keep your location on.');
    }
    permission = await Geolocator.requestPermission();
    if (permission == LocationPermission.denied) {
      permission = await Geolocator.requestPermission();
      if (permission == LocationPermission.denied) {
        Fluttertoast.showToast(msg: 'Location permission is denied.');
      }
    }
    if (permission == LocationPermission.deniedForever) {
      Fluttertoast.showToast(msg: 'Location permission is denies forever.');
    }
    Position position = await Geolocator.getCurrentPosition(
        desiredAccuracy: LocationAccuracy.high);
    try {
      List<Placemark> placemark =
          await placemarkFromCoordinates(position.latitude, position.longitude);
      Placemark place = placemark[0];
      setState(() {
        currentPosition = position;
        currentAddress =
            "${place.locality},${place.postalCode},${place.country}";
      });
    } catch (e) {
      print(e);
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Location App'),
      ),
      body: Center(
        child: Column(
          children: [
            Text(
              currentAddress,
              style: TextStyle(
                fontSize: 20,
              ),
            ),
            (currentPosition != null)
                ? Text(
                    "Latitude: " + currentPosition.latitude.toString(),
                  )
                : Container(),
            (currentPosition != null)
                ? Text(
                    "Longitude: " + currentPosition.longitude.toString(),
                  )
                : Container(),
            TextButton(
              onPressed: () {
                _determinePosition();
              },
              child: Text('Locate Me'),
            ),
          ],
        ),
      ),
    );
  }
}

Answer 1

改为：

 currentPosition!.latitude.toString()

由于您检查 currentPosition 不为空，您可以使用 ! 来表示“我知道它可以为空，但我也知道此时它肯定不是” .

属性 'latitude' 不能无条件访问，因为接收者可以是 'null'。尝试使访问有条件（使用“？”）

The property 'latitude' can't be unconditionally accessed because the receiver can be 'null'. Try making the access conditional (using '?.')

geolocation

flutter

dart-null-safety