在 null 值上使用的 Null 检查运算符 当我刷新主页或转到主页时

问：

我想我在这里需要帮助。我的代码显示错误“Null Check Operator Used on A null Value”。当我第一次运行/构建应用程序时，一切都很好。apk运行良好。但是，当我单击主页按钮或刷新TextSpan识别器时，会显示空检查警报。您能否看到下面的代码并给我解决此问题的方法。对不起，如果我的英语不好，我希望你能理解问题所在。请帮助:)

import 'dart:async';
import 'dart:convert';
import 'package:adhan/adhan.dart';
import 'package:convex_bottom_bar/convex_bottom_bar.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';
import 'package:font_awesome_flutter/font_awesome_flutter.dart';
import 'package:geocoding/geocoding.dart' as MyLocation;
import 'package:get/get.dart';
import 'package:hijri/hijri_calendar.dart';
import 'package:location/location.dart';
import 'package:intl/intl.dart';
import 'package:muslimapk/pages/kiblat_page.dart';


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

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  int currentIndexPage = 0;
  String locale = 'id';
  final location = new Location();
  String? locationError, _timenow, _datenow, _tglHijriah, _hari;
  String? MylocationCountry, MylocationCity , shalatTime ;
  PrayerTimes? prayerTimes;
  double? latitude, longitude, pLat, pLong;
  HijriCalendar? _todayhijr;


  @override
  void initState() {
    _todayhijr = HijriCalendar.now();
    _tglHijriah = _todayhijr!.toFormat("MMMM, dd yyyy H");
    _timenow = "${DateTime.now().hour} : ${DateTime.now().minute} }";
    Timer.periodic(Duration(seconds:1), (Timer t)=>_getCurrentTime());


    if (DateTime.now().hour >= 05 && DateTime.now().hour <= 06) {
      shalatTime = "Subuh";
    }if (DateTime.now().hour >= 06 && DateTime.now().hour <= 07) {
      shalatTime = "Matahari Terbit";
    }if (DateTime.now().hour >= 12 && DateTime.now().hour <= 15) {
      shalatTime = "Dzuhur";
    }if (DateTime.now().hour >= 15 && DateTime.now().hour <= 18) {
      shalatTime = "Ashar";
    }if (DateTime.now().hour >= 18 && DateTime.now().hour <= 20) {
      shalatTime = "Maghrib";
    }if (DateTime.now().hour >= 20 && DateTime.now().hour <= 05) {
      shalatTime = "Isya";
    }

    getLocationData().then((locationData) async {
      if (!mounted) {
        return;
      }
      if (locationData != null)  {

        setState(() {
          prayerTimes = PrayerTimes(
              Coordinates(locationData.latitude, locationData.longitude),
              DateComponents.from(DateTime.now()),
              CalculationMethod.karachi.getParameters());
          pLat = prayerTimes!.coordinates.latitude;
          pLong = prayerTimes!.coordinates.longitude;
          print("Latitude : $pLat, Longitude : $pLong");
        });
      } else {
        setState(() {
          locationError = "Couldn't Get Your Location!";
        });
      }
      List<MyLocation.Placemark> placemarks = await MyLocation.placemarkFromCoordinates(pLat!, pLong!);
      setState(() {

        MylocationCountry = placemarks.reversed.last.country.toString();
        MylocationCity = placemarks.reversed.last.locality.toString();
        print("Country : $MylocationCountry, City : $MylocationCity");
        print("Tanggal hijriah : $_todayhijr");
        print("Time Now : $_timenow");
      });
    });

    //DateTime.now().hour >= 18 && DateTime.now().hour <= 19

    super.initState();
  }


  @override
  Widget build(BuildContext context) {
    HijriCalendar.setLocal(locale);
    return Scaffold(
      appBar: PreferredSize(
        preferredSize: Size.fromHeight(225),
        child: AppBar(
          automaticallyImplyLeading: false,
          title: Builder(
              builder: (BuildContext context) {
                final prayerTimes = this.prayerTimes;
                if (prayerTimes != null) {
                  return RichText(
                      text: TextSpan(
                        text: MylocationCountry ?? "NULL",
                        recognizer: TapGestureRecognizer()
                          ..onTap = () {
                            Navigator.of(context).pushNamed('/home');
                          },
                        style: TextStyle(
                          fontSize: 18,
                          fontWeight: FontWeight.w500,
                        ),
                          children: [
                            TextSpan(
                              text: "\n$MylocationCity" ,
                              recognizer: TapGestureRecognizer()
                                ..onTap = () {
                                  Navigator.of(context).pushNamed('/home');
                                },
                              style: TextStyle(
                                fontSize: 16,
                                fontWeight: FontWeight.normal,
                              ),
                            ),
                            WidgetSpan(
                              alignment: PlaceholderAlignment.middle,
                              child: Icon(
                                Icons.refresh_rounded,
                                color: Colors.white,
                              )

                            ),
                          ],
                      )

                  );
                }
                if (locationError != null) {
                  return Text(locationError!);
                }
                return CircularProgressIndicator(
                  color: Colors.white,
                );
              }
          ),
          flexibleSpace: ClipRect(
            child: Container(
              decoration: BoxDecoration(
                image: DecorationImage(
                  image: AssetImage("lib/images/masjidil-aqsha.jpg"),
                  fit: BoxFit.fill,
                  colorFilter: ColorFilter.mode(
                      Color(0xFF002700).withOpacity(0.50), BlendMode.darken)
                ),
              ),
            ),
          ),
          bottom: PreferredSize(
            preferredSize: Size.fromHeight(200),
            child: Column(
            children: [
              Text(shalatTime ?? "NULL",
                style: TextStyle(
                    fontSize: 24,
                    color: Colors.white),),
             SizedBox( height: 10 ),
              Text(_timenow ?? "NULL",
                style: TextStyle(
                    fontSize: 40,
                    color: Colors.white),),
              SizedBox( height: 10 ),
              Text( _tglHijriah ?? "NULL",
                style: TextStyle(
                    fontSize: 24,
                    color: Colors.white),),
              SizedBox( height: 10 ),
            ],
            ),
          ),
          shape: RoundedRectangleBorder(
              borderRadius: BorderRadius.only(
                  bottomLeft: Radius.circular(0),
                  bottomRight: Radius.circular(0))
          ),
          actions: <Widget>[
            Container(
              margin: EdgeInsets.all(10),
              height: 250,
              child: RichText(
                text: TextSpan(
                  text: "$_datenow",
                  style: TextStyle(
                    fontSize: 16,
                    fontWeight: FontWeight.w500,
                  ),
                  children: [
                    TextSpan(
                      text: "\n$_hari",
                      style: TextStyle(
                        fontSize: 18,
                        fontWeight: FontWeight.normal,
                      ),
                    ),
                  ],
                )
              ))],
        ),
      ),

      extendBodyBehindAppBar: false,

      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Builder(
              builder: (BuildContext context) {
                final prayerTimes = this.prayerTimes;
                if (prayerTimes != null) {
                  return Column(
                    children: [
                      Text(
                        'Prayer Times for Today',
                        textAlign: TextAlign.center,
                        style: TextStyle(color: Colors.white),
                      ),
                      Text('Fajr Time: ' +
                          DateFormat("HH:mm").format(prayerTimes.fajr),
                          style: TextStyle(color: Colors.white),),
                      Text('Sunrise Time: ' +
                          DateFormat("HH:mm").format(prayerTimes.sunrise),
                          style: TextStyle(color: Colors.white),),
                      Text('Dhuhr Time: ' +
                          DateFormat("HH:mm").format(prayerTimes.dhuhr),
                          style: TextStyle(color: Colors.white),),
                      Text('Asr Time: ' +
                          DateFormat("HH:mm").format(prayerTimes.asr),
                          style: TextStyle(color: Colors.white),),
                      Text('Maghrib Time: ' +
                          DateFormat("HH:mm").format(prayerTimes.maghrib),
                          style: TextStyle(color: Colors.white),),
                      Text('Isha Time: ' +
                          DateFormat("HH:mm").format(prayerTimes.isha),
                          style: TextStyle(color: Colors.white),),
                    ],
                  );
                }
                if (locationError != null) {
                  return Text(locationError!);
                }
                return CircularProgressIndicator(
                  color: Colors.white,
                );
              },
            )
          ],
        ),
      ),

      bottomNavigationBar: ConvexAppBar(
          style: TabStyle.react,
          backgroundColor: Color(0xFF018700),
          top: -20,
          items: [
            TabItem(icon: Icons.home, title: 'Beranda'),
            TabItem(icon: Icons.navigation, title: 'Kiblat'),
            TabItem(icon: Icons.calendar_month, title: 'Kalender'),
            TabItem(icon: Icons.settings, title: 'Pengaturan'),
          ],
          initialActiveIndex: currentIndexPage,
          onTap: (int index) {
            currentIndexPage = index;
            if(index == 0) {
              Navigator.of(context).pushNamed('/home');
            }
            if(index == 1) {
              Navigator.of(context).pushNamed('/kiblat');
            }
            if(index == 2) {
              Navigator.of(context).pushNamed('/calendar');
            }
            if(index == 3) {
              Navigator.of(context).pushNamed('/settings');
            }
          }
      ),
    );
  }

  Future<LocationData?> getLocationData() async {
    var _serviceEnabled = await location.serviceEnabled();
    if (!_serviceEnabled) {
      _serviceEnabled = await location.requestService();
      if (!_serviceEnabled) {
        return null;
      }
    }

    var _permissionGranted = await location.hasPermission();
    if (_permissionGranted == PermissionStatus.denied) {
      _permissionGranted = await location.requestPermission();
      if (_permissionGranted != PermissionStatus.granted) {
        return null;
      }
    }

    return await location.getLocation();
  }

  void _getCurrentTime()  {
    setState(() {
      _timenow = DateFormat('hh:mm').format(DateTime.now());
      _datenow = DateFormat.yMMMMd("id").format(DateTime.now().toLocal());
      _hari    = DateFormat.EEEE("id").format(DateTime.now());
    });
  }
}

我试图用“！”进行checknull，但警报仍然显示。当我去或刷新主路线时，就会发生这种情况。