我的StatefulWidget中的List就是这种情况

Question

颤振

import 'package:country_house/pages/Country.dart';
import 'package:dio/dio.dart';
import 'package:flutter/material.dart';
class AllCountries extends StatefulWidget {
const AllCountries({Key? key}) : super(key: key);
@override
State<AllCountries> createState() => _AllCountriesState();
}
class _AllCountriesState extends State<AllCountries> {
Future<List> countries=[];
Future<List> getCountries() async {
var response = await Dio().get('https://restcountries.com/v3.1/all');
return response.data.length;
}
@override
void initState() {
countries = getCountries();
super.initState();
}
@override
Widget build(BuildContext context) {
getCountries();
return Scaffold(
appBar: AppBar(
title: Text('All Countries'),
centerTitle: true,
),
body: Container(
child: Padding(
padding: const EdgeInsets.all(10.0),
child: FutureBuilder<List>(
future: countries,
builder: (BuildContext context, AsyncSnapshot<List> snapshot) {
if (snapshot.hasData) {
return Text('hello');
}
return null;
}),

),
),
);
}
}

我得到以下错误：不能将类型为"List"的值分配给类型为"Future<列出>'。

• "列表"来自"dart:core">
• "Future"来自"dart:async"。未来国家=[]

如何解决此问题？

Answer 1

您必须以以下形式声明countries：
Future<List> countries = Future.value([]);

class _AllCountriesState extends State<AllCountries> {
Future<List> countries = Future.value([]);
Future<List> getCountries() async {
var response = await Dio().get('https://restcountries.com/v2/all');
return response.data;
}
@override
void initState() {
countries = getCountries();
super.initState();
}

Answer 2

您必须将countries声明为后期Future:

late Future<List> countries;

然后，initState()就会工作。请注意，您请求的是响应的长度，而不是数据。为了填充列表，您还应该解析jSon数据。您可以在以下链接中阅读使用Dio在flutter中联网的示例：使用Dio 在flutter进行联网