flutter - 类型 'String' 不是类型“Widget”的子类型？在 Dart 中

Question

我是 Flutter 的新手。我做了一个 flutter 项目，它从 API 获取数据并将它们显示在 ListView 中。如果 snapShot 中没有数据，则会显示加载屏幕。

我在修复了一些小错误后运行程序时出现错误。

错误:类型“String”不是类型“Widget”的子类型？

我的代码:

import 'dart:convert';

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

class DataFromAPI extends StatefulWidget {
  const DataFromAPI({Key? key}) : super(key: key);

  @override
  State<DataFromAPI> createState() => _DataFromAPIState();
}

class _DataFromAPIState extends State<DataFromAPI> {

  getUserData() async{
    var response = await http.get(Uri.parse('https://jsonplaceholder.typicode.com/users'));
    var jsonData = jsonDecode(response.body);
    print(response.body);
    List<User> users = [];

    for(var u in jsonData){
      User user = User(u['name'],u['email'],u['username']);
      users.add(user);
    }
    //print(users.length);
    return users;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Get Data From API'),
      ),
      body: Container(
        child: Card(
          child: FutureBuilder(
            future: getUserData(),
            builder: (context, AsyncSnapshot snapShot){
              if(snapShot.data == null){
                return Container(child: Center(child: Text('Loading'),),);
              }else{
                return ListView.builder(
                    itemCount: snapShot.data.length,
                    itemBuilder: (context, i){
                      return ListTile(title: snapShot.data[i].name);
                    });
              }
            },
          ),
    ))
    );
  }
}

class User{
  final String name, email, userName;
  User(this.name, this.email, this.userName);
}

控制台输出:

Syncing files to device sdk gphone64 x86 64...
Reloaded 0 libraries in 506ms (compile: 12 ms, reload: 0 ms, reassemble: 433 ms).
D/EGL_emulation( 6751): app_time_stats: avg=8895.54ms min=975.35ms max=16815.74ms count=2

======== Exception caught by widgets library =======================================================
The following _TypeError was thrown building:
type 'String' is not a subtype of type 'Widget?'

Answer 1

您的错误来自于您正在尝试创建一个 ListTile 小部件，并且作为标题您正在传递一个 String 。

但是如果你看一下 documentation对于 ListTile，您可以看到它期望标题是一个文本小部件:

Container(
  color: Colors.green,
  child: const Material(
    child: ListTile(
      title: Text('ListTile with red background'),
      tileColor: Colors.red,
    ),
  ),
)

因此您需要将代码更改为:

 @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Get Data From API'),
      ),
      body: Container(
        child: Card(
          child: FutureBuilder(
            future: getUserData(),
            builder: (context, AsyncSnapshot snapShot){
              if(snapShot.data == null){
                return Container(child: Center(child: Text('Loading'),),);
              }else{
                return ListView.builder(
                    itemCount: snapShot.data.length,
                    itemBuilder: (context, i){
                      return ListTile(title: const Text(snapShot.data[i].name)); //// <---------------------
                    });
              }
            },
          ),
    ))
    );
  }