如何创建一个 Flutter Futurebuilder 函数来显示从 JSON 中获取的字符串数组？

Posted 2023-02-23

【中文标题】如何创建一个 Flutter Futurebuilder 函数来显示从 JSON 中获取的字符串数组？

【英文标题】：How do I create a Flutter Futurebuilder function that displays an array of Strings taken from JSON?

【发布时间】：2019-09-12 16:22:12

【问题描述】：

我在 Flutter 中有一个项目管理应用程序，并将这些项目排列在一个列表视图中。我以 JSON 格式从 API 获取数据，并希望显示正在处理该项目的用户！

JSON：

"id": 81,
"users": [
    
        "username": "hugo",
        "fullname": "Hugo Johnsson"
    ,
    
        "username": "studentone",
        "fullname": "Student One"
    
],
"title": "test med teacher chat",
"description": "This project does not have a description.",
"subject": "No subject",
"deadline": "2019-01-06",
"days_left": "107 days ago",
"overview_requests": [
    
        "id": 28,
        "user": 
            "username": "hugo",
            "fullname": "Hugo Johnsson"
        ,
        "group": 81
    
]

Flutter 中的类：

class Project 
  final int id;
  final String title;
  final String description;
  final String deadline;
  final String subject;
  final String days_left;
  final List<USER> users;

  Project(
      this.id,
      this.title,
      this.description,
      this.deadline,
      this.subject,
      this.days_left,
      this.users
  );


class USER 
  final String username;
  final String fullname;

USER(
  this.username,
  this.fullname
  );

未来（用于 Futurebuilder）：

   Future<List<Project>> _getProjects() async 
   var data = await http.get(--ADRESS--);
   var jsonData = json.decode(data.body); //an array of json objects

   List<Project> allProjects = [];

   for (var JData in jsonData) 
     Project project = Project(
         JData["id"],
         JData["title"],
         JData["description"],
         JData["deadline"],
         JData["subject"],
         JData["days_left"],
         JData[USER("username", "fullname")]

     allProjects.add(project);
   

   return allProjects;
 

UI 存在一个返回 listview.builder 的 futurebuilder。未来是上面的功能，我想在另一个列表视图中显示用户名。

So this is what I want it to look like, the difference is that the Text inside the Circle Avatars should be the fist letters of the usernames

如何取出字符串？

Text(snapshot.data[index].users.username

【参考方案1】：

小部件

Widget build(BuildContext context) 
  return FutureBuilder(
    future: _getProjects(),
    builder: (context, snapshot) => ListView.builder(
      itemCount: snapshot.data.length,
      itemBuilder: (context, index) => ListView.builder(
        itemCount: snapshot.data[index].users.length,
        itemBuilder: (context, userIndex) => Text(snapshot.data[index].users[userIndex].username[0]),
      ),
    ),
  );

服务

Future<List<Project>> _getProjects() async 
  var data = await http.get(--ADRESS--);
  var jsonData = json.decode(data.body); //an array of json objects

  List<Project> allProjects = [];

  for (var JData in jsonData) 

    List<USER> users = JData["users"] == null 
      ? [] 
      : JData["users"]
          .map( (userJson) => USER("username", "fullname") ) // new code

    Project project = Project(
      JData["id"],
      JData["title"],
      JData["description"],
      JData["deadline"],
      JData["subject"],
      JData["days_left"],
      users,
    );

    allProjects.add(project);
 

 return allProjects;

【讨论】：

flutter：引发了另一个异常：NoSuchMethodError：在 null 上调用了 getter 'length'。颤振：抛出另一个异常：NoSuchMethodError：方法'[]'在null上被调用。

仍然错误 The getter 'length' was called on null

可能您的用户列表为空。检查您的 _getprojects 功能。在此之后您必须进行调试。

我知道但我不明白怎么做：JData[USER("username", "fullname")]

你有什么想法吗？