“String”类型不是“Widget”类型的子类型？ 在 flutter dart

Question

I am new to Flutter. I made a flutter project that gets data from an API and displays them in a ListView. And if no data in snapShot then shows a loading screen.

I got an error when I ran the program after fixing some small errors.

Error: type 'String' is not a subtype of type 'Widget?

My Code:

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);
}

Console Output:

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

Your error comes from the fact that you are trying to create a ListTile widget and as the title you are passing in a String .

But if you look at the documentation for ListTile, you can see that it expects the title to be a Text widget :

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

So you need to change your code to this:

 @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)); //// <---------------------
                    });
              }
            },
          ),
    ))
    );
  }

Answer 2

You have to add widget to ListTile title, based on your requirements than you can assign text value to it.

Here for string you can use Text widget

itemBuilder: (context, i) {
     return ListTile(title: Text(snapShot.data[i].name));
}

Answer 3

List view title takes a widget, you need to pass a widget not a string that what you are doing right now.

just wrap your title string in a Text widget.

itemBuilder: (context, i){
                  return ListTile(title: Text(snapShot.data[i].name??''));
                });

Answer 4

Change your ListTile

From

         return ListView.builder(
                itemCount: snapShot.data.length,
                itemBuilder: (context, i){
                  return ListTile(title: snapShot.data[i].name);
                });
          }

To

        return ListView.builder(
                itemCount: snapShot.data.length,
                itemBuilder: (context, i){
                  return ListTile(title: Text(snapShot.data[i].name));
                });
          }