为了快速修复，我引入了两个变量loading和error。
下面是状态_MyHomeState的代码

class _MyHomeState extends State<MyHome> {
  bool loading = true;//introduced for loading
  String? error;//introduced for handling error case
  DateTime launchTime = DateTime.now();
  String Name = '';
  String description = '';
  String agencyName = '';
  String type = '';
  String rocketName = '';
  String rocketVariant = '';
  String missionName = '';
  String orbitName = '';
  String location = '';
  String time = '';
  String date = '';

  @override
  void initState() {
    super.initState();
    fetchMyHome();
    Timer.periodic(Duration(seconds: 1), (Timer t) => updateCountdown());
  }

  void fetchMyHome() async {
    final response = await http.get(
        Uri.parse('https://lldev.thespacedevs.com/2.2.0/launch/upcoming/')
    );
    if (response.statusCode == 200) {
      final data = jsonDecode(response.body);
      final List<dynamic> results = data['results'];
      if (results.isNotEmpty) {
        final launch = results.elementAt(0);
        final launchTimeStr = launch['net'];
        launchTime = DateTime.parse(launchTimeStr).toLocal();
        final Launchname = launch['name'];
        Name = Launchname.toString();
        final descp = launch['mission']['description'];
        description = descp;
        final agenName = launch['launch_service_provider']['name'];
        agencyName = agenName;
        final typee = launch['launch_service_provider']['type'];
        type = typee;
        final r_name = launch['rocket']['configuration']['name'];
        rocketName = r_name;
        final r_variant = launch['rocket']['configuration']['variant'];
        rocketVariant = r_variant;
        final m_name = launch['mission']['name'];
        missionName = m_name;
        final orbit_name = launch['mission']['orbit']['name'];
        orbitName = orbit_name;
        final pad_location = launch['pad']['location']['name'];
        location = pad_location;
        final estimated_time = launch['net'];
        time = estimated_time;
        // final estimated_date=launch['pad']['location']['name'];
        // date=estimated_date;
      } else {
        error = 'No upcoming launches found';
        print('No upcoming launches found');
      }
    } else {
      error = 'Failed to fetch upcoming launches';
      print('Failed to fetch upcoming launches: ${response.statusCode}');
    }
    loading = false;
    setState(() {});
  }

  void updateCountdown() {
    setState(() {});
  }

  @override
  Widget build(BuildContext context) {
    if (loading) {
      return const Scaffold(body: Center(child: CircularProgressIndicator(),),);
    }
    if (error != null) {
      return Scaffold(body: Center(child: Text(error!),),);
    }
    final now = DateTime.now().toLocal();
    final duration = launchTime.difference(now);
    final days = duration.inDays;
    final hours = duration.inHours.remainder(24);
    final minutes = duration.inMinutes.remainder(60);
    final seconds = duration.inSeconds.remainder(60);
    final final_time = time.split("T");
    final date_final = final_time.elementAt(0).toString();
    final time_final = final_time.elementAt(1).toString();
    return Scaffold(
      backgroundColor: Colors.black54,
      drawer: Nav_Drawer(),

      appBar: AppBar(

        backgroundColor: Colors.black,
        title: const Text('Welcome'),
      ),
      body:
      SingleChildScrollView(
        child: Column(

          mainAxisAlignment: MainAxisAlignment.start,
          children: [
            const SizedBox(height: 20),
            Text(
              'Next Launch in:',
              style: TextStyle(
                  color: Colors.white,
                  fontSize: 24),
            ),
            const SizedBox(height: 20),

            Stack(
              alignment: Alignment.center,
              children: [
                CarouselSlider(
                  items: [
                    Image.network(
                        'https://c4.wallpaperflare.com/wallpaper/559/511/583/spacex-rocket-falcon-9-smoke-wallpaper-preview.jpg'),
                    Image.network(
                        'https://c4.wallpaperflare.com/wallpaper/81/233/257/spacex-rocket-smoke-cape-canaveral-wallpaper-preview.jpg'),
                    Image.network(
                        'https://c4.wallpaperflare.com/wallpaper/758/798/536/spacex-rocket-launch-pads-falcon-heavy-wallpaper-preview.jpg'),
                    Image.network(
                        'https://cdnn1.img.sputniknews.com/img/07e6/0a/17/1102543952_0:0:3071:1728_1920x0_80_0_0_94bf3eb33e85402d96a49a4e84e93b84.jpg'),
                    Image.network(
                        'https://static.theprint.in/wp-content/uploads/2018/03/6-01-e1530068959485.jpg?compress=true&quality=80&w=376&dpr=2.6'),
                    Image.network(
                        'https://c4.wallpaperflare.com/wallpaper/390/31/781/spacex-rocket-falcon-9-wallpaper-preview.jpg'),
                  ],
                  options: CarouselOptions(
                    height: 300,
                    // height: 200.0,
                    // enlargeCenterPage: true,
                    autoPlay: false,
                    enableInfiniteScroll: true,
                    autoPlayAnimationDuration: Duration(seconds: 3),
                    viewportFraction: 1,
                  ),
                ),
                Column(
                  children: [
                    Text(
                      '$days : $hours : $minutes : $seconds',
                      style: TextStyle(
                          fontSize: 30,
                          color: Colors.white
                      ),
                    ),
                    Text(
                      'Days : Hours : Minutes : Seconds',
                      style: TextStyle(
                          color: Colors.white,
                          fontSize: 12
                      ),
                    ),
                  ],
                ),

              ],
            ),
            Text(Name,
              style: TextStyle(
                  color: Colors.white,
                  fontSize: 20
              ),
            ),
            SizedBox(height: 20),
            Padding(
              padding: EdgeInsets.all(10),
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: [
                  Divider(
                    color: Colors.white,
                  ),
                  Text('Description:',
                    style: TextStyle(
                        color: Colors.blueAccent,
                        fontSize: 14
                    ),
                  ),

                  SizedBox(height: 4),
                  Text(description,
                    style: TextStyle(
                        color: Colors.white,
                        fontSize: 14
                    ),),
                  Divider(
                    color: Colors.white,
                  ),
                  SizedBox(height: 5),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.spaceBetween,
                    children: [
                      Text('Agency:',
                        style: TextStyle(
                          color: Colors.blueAccent,
                        ),
                      ),
                      Text(agencyName,
                        style: TextStyle(
                            color: Colors.white
                        ),
                      ),
                    ],
                  ),
                  Divider(
                    color: Colors.white,
                  ),
                  SizedBox(height: 5),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.spaceBetween,
                    children: [
                      Text('Launch type:',
                        style: TextStyle(
                          color: Colors.blueAccent,
                        ),
                      ),
                      Text(type,
                        style: TextStyle(
                            color: Colors.white
                        ),
                      ),
                    ],
                  ),
                  Divider(
                    color: Colors.white,
                  ),
                  SizedBox(height: 5),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.spaceBetween,
                    children: [
                      Text('Rocket name:',
                        style: TextStyle(
                          color: Colors.blueAccent,
                        ),
                      ),
                      Text(rocketName,
                        style: TextStyle(
                            color: Colors.white
                        ),
                      ),
                    ],
                  ),
                  Divider(
                    color: Colors.white,
                  ),
                  SizedBox(height: 5),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.spaceBetween,
                    children: [
                      Text('Rocket variant:',
                        style: TextStyle(
                          color: Colors.blueAccent,
                        ),
                      ),
                      Text(rocketVariant,
                        style: TextStyle(
                            color: Colors.white
                        ),
                      ),
                    ],
                  ),
                  Divider(
                    color: Colors.white,
                  ),
                  SizedBox(height: 5),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.spaceBetween,
                    children: [
                      Text('Mission Name:',
                        style: TextStyle(
                          color: Colors.blueAccent,
                        ),
                      ),
                      Text(missionName,
                        style: TextStyle(
                            color: Colors.white
                        ),
                      ),
                    ],
                  ),
                  Divider(
                    color: Colors.white,
                  ),
                  SizedBox(height: 5),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.spaceBetween,
                    children: [
                      Text('Orbit:',
                        style: TextStyle(
                          color: Colors.blueAccent,
                        ),
                      ),
                      Text(orbitName,
                        style: TextStyle(
                            color: Colors.white
                        ),
                      ),
                    ],
                  ),
                  Divider(
                    color: Colors.white,
                  ),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.spaceBetween,
                    children: [
                      Text('Launch Location:',
                        style: TextStyle(
                          color: Colors.blueAccent,
                        ),
                      ),
                    ],
                  ),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.end,
                    children: [
                      Text(location,
                        style: TextStyle(
                            color: Colors.white
                        ),
                      ),
                      Divider(
                        color: Colors.white,
                      )
                    ],
                  ),
                  Divider(
                    color: Colors.white,
                  ),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.spaceBetween,
                    children: [
                      Text('Date:',
                        style: TextStyle(
                          color: Colors.blueAccent,
                        ),
                      ),
                      Text(date_final,
                        style: TextStyle(
                            color: Colors.white
                        ),
                      ),
                    ],
                  ),
                  Divider(
                    color: Colors.white,
                  ),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.spaceBetween,
                    children: [
                      Text('Time:',
                        style: TextStyle(
                          color: Colors.blueAccent,
                        ),
                      ),
                      Text(time_final,
                        style: TextStyle(
                            color: Colors.white
                        ),
                      ),
                    ],
                  ),
                ],
              ),
            ),

          ],
        ),
      ),
      bottomNavigationBar: BottomNavBar(0),
    );
  }
}

当您尝试访问列表中不存在的索引值时，会出现此错误：

例如：

List list = ["a","b"];
list[4]; // <-- Range Error since there's no element at index 4 in the list,

our application tries to use value at index 4, which does not exist. 

**Solution:**

 Try to debug at a point where you are using the index value of a list.

当您尝试访问列表中不存在的索引值时，会出现此错误：

• • 例如：**

List list = ["a","b"];
list[4]; // <-- Range Error since there's no element at index 4 in the list,

我们的应用程序尝试使用索引4处的值，但该值不存在。

• • 溶液**：尝试在使用列表的索引值时进行调试。

如果您正在从和API获取数据，这是正确的方法：

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: _title,
      home: MyStatefulWidget(),
    );
  }
}


class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({super.key});

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  Future fetchResult() async {
final response = await http.get(
      Uri.parse('https://lldev.thespacedevs.com/2.2.0/launch/upcoming/');

if(response.statusCode == 200){
 final apiData = jsonDecode(response.body);
     
    return apiData;

}else{
   return null;
}

}

  @override
  Widget build(BuildContext context) {
    return DefaultTextStyle(
      style: Theme.of(context).textTheme.displayMedium!,
      textAlign: TextAlign.center,
      child: FutureBuilder(
        future: fetchResult(), // a previously-obtained Future<String> or null
        builder: (BuildContext context, AsyncSnapshot snapshot) {
          List<Widget> children;
          if (snapshot.hasData) {
           final List<dynamic> results = snapshot.data['results'];
 return  ListView.builder(
             itemCount: results.length,
            itemBuilder: (BuildContext context, int index) {
            return Container(
              width: 100,
              height: 100,
              color: Colors.red,
            );
            },
            );
          } else if (snapshot.hasError) {
            children = <Widget>[
              const Icon(
                Icons.error_outline,
                color: Colors.red,
                size: 60,
              ),
              Padding(
                padding: const EdgeInsets.only(top: 16),
                child: Text('Error: ${snapshot.error}'),
              ),
            ];
          } else {
            children = const <Widget>[
              SizedBox(
                width: 60,
                height: 60,
                child: CircularProgressIndicator(),
              ),
              Padding(
                padding: EdgeInsets.only(top: 16),
                child: Text('Awaiting result...'),
              ),
            ];
          }
          return Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: children,
            ),
          );
        },
      ),
    );
  }
}