我在我的大学服务器上托管了一个 php 文件，当我在服务器上运行该文件时，它运行良好。运行链接中的 php 文件后，我可以获得 json 数据 http://www.alkadhum-col.edu.iq/Teachers%20Activities/get.php但是当我在应用程序屏幕上的抖动中尝试时无法得到它们时得到“getter 'length'was called on null”。

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';

void main() {
runApp(Workshops());
}

class Workshops extends StatelessWidget {
  @override
  Widget build(BuildContext mycontext) {
    return MaterialApp(
      home:Scaffold(
        appBar: AppBar(
          backgroundColor: Color.fromRGBO( 52, 73, 94, 1.0),
        automaticallyImplyLeading: false, // Don't show the leading button
        title: new Text("PHP with Flutter"),
        ),

        body: PostScreen(),
        )
    );
  }
}    

class PostScreen extends StatefulWidget {
  @override
  _PostScreenState createState() => _PostScreenState();
}

class _PostScreenState extends State<PostScreen> {
  List<Post> _postList = new List<Post>();

  Future<List<Post>> fetchPost() async {
    final response =
        await http.get('http://www.alkadhum-col.edu.iq/Teachers%20Activities/get.php');

    if (response.statusCode == 200) {
      // If the call to the server was successful, parse the JSON
      List<dynamic> values = new List<dynamic>();
      values = json.decode(response.body);
      if (values.length > 0) {
        for (int i = 0; i < values.length; i++) {
          if (values[i] != null) {
            Map<String, dynamic> map = values[i];
            _postList.add(Post.fromJson(map));
          }
        }
      }
      return _postList;
    } else {
      // If that call was not successful, throw an error.
      throw Exception('Failed to load post');
    }
  }

  @override
  Widget build(BuildContext context) {
    return FutureBuilder<List<Post>>(
      future: fetchPost(),
      builder: (_, AsyncSnapshot<List<Post>> snapshot) {
        if (snapshot.connectionState == ConnectionState.waiting) {
          return Center(child: CircularProgressIndicator());
        }

        return ListView.builder(
          itemCount: snapshot.data.length,
          itemBuilder: (_, index) {
            //dynamic post = snapshot.data[index];
            return (Container(
              margin: EdgeInsets.symmetric(vertical: 2.0, horizontal: 8.0),
              child: new Card(
                elevation: 10.0,
                child: new Container(
                  child: new Column(
                    crossAxisAlignment: CrossAxisAlignment.center,
                    children: <Widget>[
                      new Text(snapshot.data[index].name, style: TextStyle(fontSize: 18.0),),
                      new Text(snapshot.data[index].msg, style: TextStyle(fontSize: 18.0),),
                      new Text(snapshot.data[index].day, style: TextStyle(fontSize: 18.0),),
                      new Text(snapshot.data[index].date, style: TextStyle(fontSize: 18.0),),
                    ],
                  ),
                ),
              ),
            ));
          },
        );
      },
    );
  }

  @override
  void initState() {
    super.initState();
    fetchPost();
  }
}

class Post {
  String name;
  String msg;
  String day;
  String date;

  Post({this.name, this.msg, this.day, this.date});

  factory Post.fromJson(Map<String, dynamic> json) {
    return Post(
      name: json['name'],
      msg: json['msg'],
      day: json['day'],
      date:json['date']
    );
  }
}

如何解决这个问题？
提前致谢。

最佳答案

我查看了您的链接并尝试运行代码，我认为问题出在从您的链接返回的数据中。

[{"name":"م.م علي ستار باراني","msg":"امتحان مادة قواعد البيانات اول جابترين ","day":"السبت","date":"2019-06-20"}][{"name":"م. امجد عباس التميمي","msg":"امتحان مادة هندسة البرامجيات اول فصلين","day":"الاحد","date":"2019-06-21"},{"name":"م.م علي ستار باراني","msg":"امتحان مادة قواعد البيانات اول جابترين ","day":"السبت","date":"2019-06-20"}]

在第一个对象之后，您有一个右方括号，并且没有逗号将它与旁边的左方括号分开。在链接主体上调用 json.decode() 会抛出以下错误

FormatException (FormatException: Unexpected character (at character 115)
...,"day":"السبت","date":"2019-06-20"}][{"name":"م. امجد عباس التميمي","msg...
                                       ^
)

修复后，它对我来说运行良好。我通过手动获取链接主体并删除有问题的字符进行测试，留下下面的 json。

[{"name":"م.م علي ستار باراني","msg":"امتحان مادة قواعد البيانات اول جابترين ","day":"السبت","date":"2019-06-20"},{"name":"م. امجد عباس التميمي","msg":"امتحان مادة هندسة البرامجيات اول فصلين","day":"الاحد","date":"2019-06-21"},{"name":"م.م علي ستار باراني","msg":"امتحان مادة قواعد البيانات اول جابترين ","day":"السبت","date":"2019-06-20"}]

现在运行该应用会显示以下内容:

关于json - 如何解决这个 "The getter ' 长度' was called on null"，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/56715903/