image - 该页面无法在我的flutter应用程序中正确加载页面(已更新)无效的参数:源不得为null

Question

我已经更新了我发布的问题:
我有页面从另一个dart文件获取小部件。
我使用提取方法而非小部件更改了一页中的所有页面，因此我从第一个函数中删除了 future :

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'package:shared_preferences/shared_preferences.dart';
import 'dart:convert';
class Home extends StatefulWidget {
  @override
  _HomeState createState() => _HomeState();
}
class _HomeState extends State<Home> {
  var username;
  var userId;
  var lang;
  var savedCourseId;
  var savedDayId;

// getting m_id from status user
  void getUserStatus() async {
    SharedPreferences preferences = await SharedPreferences.getInstance();
    setState(() {
      username = preferences.getString('username');
      userId = preferences.getString('logined_id');
      lang = preferences.getString('lang');
    });
    var url =
        "http://10.0.2.2/jiyan/test/api/users/status_user.php?username=$username";
    var response = await http.get(url);
    var data = jsonDecode(response.body);
    setState(() {
      savedCourseId = data['m_id'];
      savedDayId = int.parse(data['d_id']);
    });
  }
  @override
  void initState() {
    getUserStatus();

    super.initState();
  }
  @override
  Widget build(BuildContext context) {
    final size = MediaQuery.of(context).size.width;
    return Scaffold(
      drawer: buildDrawerMyDrawer(),
      appBar: AppBar(
        backgroundColor: Colors.pink[900],
        title: Text(
          'ژیان و قورئان',
          style: TextStyle(fontSize: 32),
        ),
        centerTitle: true,
      ),
      body: Container(
        padding: const EdgeInsets.only(top: 20),
        decoration: BoxDecoration(
            image: DecorationImage(
          image: AssetImage('./assets/images/background.png'),
          fit: BoxFit.cover,
        )),
        child: Directionality(
          textDirection: TextDirection.rtl,
          child: ListView(
            children: [
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceAround,
                children: [
                  buildContainer(size, 1, userId, savedCourseId),
                  buildContainer(size, 2, userId, savedCourseId),
                  buildContainer(size, 3, userId, savedCourseId),
                ],
              ),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                children: [
                  buildContainer(size, 4, userId, savedCourseId),
                  buildContainer(size, 5, userId, savedCourseId),
                ],
              ),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceAround,
                children: [
                  buildContainer(size, 6, userId, savedCourseId),
                  buildContainer(size, 7, userId, savedCourseId),
                  buildContainer(size, 8, userId, savedCourseId),
                ],
              ),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                children: [
                  buildContainer(size, 9, userId, savedCourseId),
                  buildContainer(size, 10, userId, savedCourseId),
                ],
              ),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceAround,
                children: [
                  buildContainer(size, 11, userId, savedCourseId),
                  buildContainer(size, 12, userId, savedCourseId),
                  buildContainer(size, 13, userId, savedCourseId),
                ],
              ),
            ],
          ),
        ),
      ),
    );
  }
//
  Container buildContainer(size, courseId, userID, savedCourseId) {
    return Container(
      width: 0.25 * size,
      child: InkWell(
        onTap: courseId <= int.parse(savedCourseId)
            ? () {
                Navigator.of(context).pushNamed('weeks', arguments: {
                  'courseId': courseId,
                  'lang': lang,
                  'savedDayId': savedDayId,
                  'savedCourseID': int.parse(savedCourseId),
                  'userID': userID,
                });
              }
            : null,
        child: Image(
          image: AssetImage(courseId <= int.parse(savedCourseId)
              ? './assets/images/months/course' + courseId.toString() + '.png'
              : './assets/images/months/course' +
                  courseId.toString() +
                  'c.png'),
        ),
      ),
    );
  }
}

现在，先前的错误已修复，但是出现错误，然后页面成功加载，并在Debug Console上显示了此错误:

Invalid argument(s): The source must not be null

我现在该如何解决？

Answer 1

经过多次测试，我发现错误是由saveCourseId变量引起的，在加载页面时该数据具有null数据，因此它给了我这个错误，因此我添加了一条条件语句，如果saveCourseId的值为null则只显示conatiner否则显示页面详细信息，因此现在没有错误:
页面是这样的:

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'package:shared_preferences/shared_preferences.dart';
import 'dart:convert';
class Home extends StatefulWidget {
  @override
  _HomeState createState() => _HomeState();
}
class _HomeState extends State<Home> {
  var username;
  var userId;
  var lang;
  var savedCourseId;
  var savedDayId;

// getting m_id from status user
  void getUserStatus() async {
    SharedPreferences preferences = await SharedPreferences.getInstance();
    setState(() {
      username = preferences.getString('username');
      userId = preferences.getString('logined_id');
      lang = preferences.getString('lang');
    });
    var url =
        "http://10.0.2.2/jiyan/test/api/users/status_user.php?username=$username";
    var response = await http.get(url);
    var data = jsonDecode(response.body);
    setState(() {
      savedCourseId = data['m_id'];
      savedDayId = int.parse(data['d_id']);
    });
  }
  @override
  void initState() {
    getUserStatus();

    super.initState();
  }
  @override
  Widget build(BuildContext context) {
    final size = MediaQuery.of(context).size.width;
    return Scaffold(
      drawer: buildDrawerMyDrawer(),
      appBar: AppBar(
        backgroundColor: Colors.pink[900],
        title: Text(
          'ژیان و قورئان',
          style: TextStyle(fontSize: 32),
        ),
        centerTitle: true,
      ),
      body: Container(
        padding: const EdgeInsets.only(top: 20),
        decoration: BoxDecoration(
            image: DecorationImage(
          image: AssetImage('./assets/images/background.png'),
          fit: BoxFit.cover,
        )),
        child: Directionality(
          textDirection: TextDirection.rtl,
          child: savedCourseId != null //---------Add this condition
            ? ListView(
                children: [
                  Row(
                    mainAxisAlignment: MainAxisAlignment.spaceAround,
                    children: [
                      buildContainer(size, 1, userId, savedCourseId),
                      buildContainer(size, 2, userId, savedCourseId),
                      buildContainer(size, 3, userId, savedCourseId),
                    ],
                  ),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                    children: [
                      buildContainer(size, 4, userId, savedCourseId),
                      buildContainer(size, 5, userId, savedCourseId),
                    ],
                  ),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.spaceAround,
                    children: [
                      buildContainer(size, 6, userId, savedCourseId),
                      buildContainer(size, 7, userId, savedCourseId),
                      buildContainer(size, 8, userId, savedCourseId),
                    ],
                  ),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                    children: [
                      buildContainer(size, 9, userId, savedCourseId),
                      buildContainer(size, 10, userId, savedCourseId),
                    ],
                  ),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.spaceAround,
                    children: [
                      buildContainer(size, 11, userId, savedCourseId),
                      buildContainer(size, 12, userId, savedCourseId),
                      buildContainer(size, 13, userId, savedCourseId),
                    ],
                  ),
                ],
              )
            : Container()),
      ),
    );
  }
//
  Container buildContainer(size, courseId, userID, savedCourseId) {
    return Container(
      width: 0.25 * size,
      child: InkWell(
        onTap: courseId <= int.parse(savedCourseId)
            ? () {
                Navigator.of(context).pushNamed('weeks', arguments: {
                  'courseId': courseId,
                  'lang': lang,
                  'savedDayId': savedDayId,
                  'savedCourseID': int.parse(savedCourseId),
                  'userID': userID,
                });
              }
            : null,
        child: Image(
          image: AssetImage(courseId <= int.parse(savedCourseId)
              ? './assets/images/months/course' + courseId.toString() + '.png'
              : './assets/images/months/course' +
                  courseId.toString() +
                  'c.png'),
        ),
      ),
    );
  }
}