Image 该页面可以'；t在我的颤振应用程序（更新）中正确加载页面无效参数：源不能为null

我已经更新了我发布的问题： 我已从另一个dart文件获取页面小部件。 我使用extract方法而不是widget更改了一个页面中的所有页面，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'),
        ),
      ),
    );
  }
}

---

现在如何解决此问题？

经过多次测试后，我发现错误是由savedCourseId变量引起的，在加载页面时，它有空数据，因此它给了我此错误，在我添加条件语句之前，如果savedCourseId的值为空，请显示conatiner，否则显示页面详细信息，因此现在没有发现错误： 页面如下所示：

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'),
        ),
      ),
    );
  }
}

导入“包装：颤振/材料.省道”；
将“package:http/http.dart”导入为http；
导入“package:shared_preferences/shared_preferences.dart”；
导入“dart:convert”；
类Home扩展了StatefulWidget{
@凌驾
_HomeState createState（）=>\u HomeState（）；
}
类(HomeState扩展状态){
var用户名；
var用户id；
瓦朗；
var savedCourseId；
var-savedDayId；
//正在从状态用户获取m_id
void getUserStatus（）异步{
SharedReferences首选项=等待SharedReferences.getInstance（）；
设置状态（）{
username=preferences.getString（'username'）；
userId=preferences.getString（'logined_id'）；
lang=preferences.getString（'lang'）；
});
变量url=
"http://10.0.2.2/jiyan/test/api/users/status_user.php?username=$username”；
var response=wait http.get（url）；
var data=jsonDecode（response.body）；
设置状态（）{
savedCourseId=data['m_id']；
savedDayId=int.parse（数据['d_id']）；
});
}
@凌驾
void initState（）{
getUserStatus（）；
super.initState（）；
}
@凌驾
小部件构建（构建上下文）{
最终大小=MediaQuery.of（context）.size.width；
返回脚手架(
抽屉：buildDrawerMyDrawer（），
appBar:appBar(
背景颜色：颜色。粉红色[900]，
标题：正文(
'ژیان و قورئان',
样式：TextStyle（字体大小：32），
),
标题：对，
),
主体：容器(
填充：仅限常量边集（顶部：20），
装饰：盒子装饰(
图像：装饰图像(
image:AssetImage（'./assets/images/background.png'），
适合：BoxFit.cover，
)),
孩子：方向性(
textDirection:textDirection.rtl，
子项：savedCourseId！=null/-----------添加此条件
？列表视图(
儿童：[
划船(
mainAxisAlignment:mainAxisAlignment.spaceAround，
儿童：[
buildContainer（大小，1，用户ID，savedCourseId），
buildContainer（大小，2，用户ID，savedCourseId），
buildContainer（大小，3，用户ID，savedCourseId），
],
),
划船(
mainAxisAlignment:mainAxisAlignment.space，
儿童：[
buildContainer（大小，4，用户ID，savedCourseId），
buildContainer（大小，5，用户ID，savedCourseId），
],
),
划船(
mainAxisAlignment:mainAxisAlignment.spaceAround，
儿童：[
buildContainer（大小，6，用户ID，savedCourseId），
buildContainer（大小，7，用户ID，savedCourseId），
buildContainer（大小，8，用户ID，savedCourseId），
],
),
划船(
mainAxisAlignment:mainAxisAlignment.space，
儿童：[
buildContainer（大小，9，用户ID，savedCourseId），
buildContainer（大小，10，用户ID，savedCourseId），
],
),
划船(
mainAxisAlignment:mainAxisAlignment.spaceAround，
儿童：[
buildContainer（大小，11，用户ID，savedCourseId），
buildContainer（大小，12，用户ID，savedCourseId），
buildContainer（大小，13，用户ID，savedCourseId），
],
),
],
)
：Container（）），
),
);
}
//
容器buildContainer（大小、courseId、用户ID、savedCourseId）{
返回容器(
宽度：0.25*尺寸，
孩子：InkWell(
onTap:courseId经过多次测试，我发现错误是由savedCourseId变量引起的，在加载页面时它有空数据，因此它给了我这个错误，在我添加条件语句之前，如果savedCourseId的值为空，只需显示conatiner，否则显示页面详细信息，因此现在没有发现错误：
页面如下所示：

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'),
        ),
      ),
    );
  }
}

导入“包装：颤振/材料.省道”；
将“package:http/http.dart”导入为http；
导入“package:shared_preferences/shared_preferences.dart”；
导入“dart:convert”；
类Home扩展了StatefulWidget{
@凌驾
_HomeState createState（）=>\u HomeState（）；
}
类(HomeState扩展状态){
var用户名；
var用户id；
瓦朗；
var savedCourseId；
var-savedDayId；
//正在从状态用户获取m_id
void getUserStatus（）异步{
SharedReferences首选项=等待SharedReferences.getInstance（）；
设置状态（）{
username=preferences.getString（'username'）；
userId=preferences.getString（'logined_id'）；
lang=preferences.getString（'lang'）；
});
变量url=
"http://10.0.2.2/jiyan/test/api/users/status_user.php?username=$username”；
var response=wait http.get（url）；
var data=jsonDecode（response.body）；
设置状态（）{
savedCourseId=data['m_id']；
savedDayId=int.parse（数据['d_id']）；
});
}
@凌驾
void initState（）{
getUserStatus（）；
super.initState（）；
}
@凌驾
小部件构建（BuildC）