flutter - 将异步值返回给 initState()

Question

我的以下代码运行良好，从 url 读取 csv 数据并打印输出：

import 'package:flutter/material.dart';
import 'dart:convert';
import 'dart:io';
import 'dart:async';
import 'package:csv/csv.dart';

void fetchUserData() async {
  final request = await HttpClient().getUrl(Uri.parse(
      'https://docs.google.com/spreadsheets/d/e/2PACX-1vQvf9tp4-fETDJbC-HRmRKvVFAXEAGO4lrYPpVeiYkB6nqqXdSs3CjX0eBMvjIoEeX9_qU6K2RWmzVk/pub?gid=0&single=true&output=csv'));
  final response = await request.close();
  List<List<dynamic>> rowsAsListOfValues;
  await for (final csvString in response.transform(const Utf8Decoder())) {
    rowsAsListOfValues =
        const CsvToListConverter().convert(csvString);
  }
  print(rowsAsListOfValues);
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  void initState() {
    super.initState();
    fetchUserData();
  }

  @override
  Widget build(BuildContext context) { // ... // }
}

我不需要打印输出，而是需要将其返回到一个变量中，我可以在 y 小部件中显示该变量，我尝试按如下方式进行：

Future<List<List<dynamic>>> fetchUserData() async {   /// change
  final request = await HttpClient().getUrl(Uri.parse(
      'https://docs.google.com/spreadsheets/d/e/2PACX-1vQvf9tp4-fETDJbC-HRmRKvVFAXEAGO4lrYPpVeiYkB6nqqXdSs3CjX0eBMvjIoEeX9_qU6K2RWmzVk/pub?gid=0&single=true&output=csv'));
  final response = await request.close();
  List<List<dynamic>> rowsAsListOfValues;
  await for (final csvString in response.transform(const Utf8Decoder())) {
    rowsAsListOfValues =
        const CsvToListConverter().convert(csvString);
  }

  return rowsAsListOfValues;    /// change
}

class _MyHomePageState extends State<MyHomePage> {
  var rowsAsListOfValues;  /// new

  @override
  void initState() {
    super.initState();
    rowsAsListOfValues = fetchUserData();    /// new
    print(rowsAsListOfValues);   /// new
  }

  @override
  Widget build(BuildContext context) { // ... // }
}

但我得到的输出为I/flutter ( 7505): Instance of 'Future<List<List<dynamic>>>'

我该如何解决？

标签： flutterdart

Answer 1

在这种情况下，您需要从 initState 切换到 didChangeDependency。因为你需要等待一些进程，而你不能在 initState 中等待。但是你可以这样等待

@override
void didChangeDependencies() async {
  super.didChangeDependencies();
  rowsAsListOfValues = await fetchUserData();
  super.setState(() {}); // to update widget data
  /// new
  print(rowsAsListOfValues);
}

这就是结果

I/flutter (24313): [[vranches], [Dammam, 2], [Khobar, 3]]