方法'[]'不能無條件呼叫，因為接收者可以為'null'。無法修復此問題

正在 youtube 上觀看一些 flutter 教程并練習使用 flutter 制作一些應用程式。當他運行代碼時，相同的代碼在導師身上效果很好，但我面臨這個錯誤，即無法無條件呼叫方法“[]”，因為接收器可以為“空”。我附上了我的代碼。也嘗試添加空檢查運算子但沒有作業。錯誤發生在第 55 行，即title: Text(myData[index]['body'])

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

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomePage(),
    );
  }
}

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

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  void initState() {
    super.initState();
  }

  Future getData() async {
    http.Response response = await http
        .get(Uri.parse("https://jsonplaceholder.typicode.com/posts/"));
    if (response.statusCode == HttpStatus.ok) {
      var result = jsonDecode(response.body);
      return result;
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("WIFI CONNECTIVITY"),
      ),
      body: FutureBuilder(
        builder: (context, snapshot) {
          if (snapshot.hasData) {
            var myData = snapshot.data;
            return ListView.builder(
              itemBuilder: (context, index) => ListTile(
                title: Text(myData[index]['body']),
              ),
            );
          } else {
            return const Center(
              child: CircularProgressIndicator(
                color: Colors.black,
              ),
            );
          }
        },
      ),
    );
  }
}

uj5u.com熱心網友回復：

使用 FutureBuilder

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

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomePage(),
    );
  }
}

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

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  Future getData() async {
    var response = await http
        .get(Uri.parse("https://jsonplaceholder.typicode.com/posts/"));
    if (response.statusCode == 200) {
      var result = jsonDecode(response.body);
      return result;
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("WIFI CONNECTIVITY"),
      ),
      body: FutureBuilder(
        future: getData(),
        builder: (context, snapshot) {
          if (snapshot.hasData) {
            var mydata = snapshot.data as List;
            return ListView.builder(itemBuilder: (context, index) {
              return Container(
                decoration: BoxDecoration(border: Border.all()),
                child: Text(mydata[index]['body']),
              );
            });
          } else {
            return const Center(
              child: CircularProgressIndicator(
                color: Colors.black,
              ),
            );
          }
        },
      ),
    );
  }
}

uj5u.com熱心網友回復：

我找不到修復程式，但我以不同的方式重寫了代碼，這里是代碼......

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

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomePage(),
    );
  }
}

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

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  var _postJson = [];

  final url = "https://jsonplaceholder.typicode.com/posts/";

  void fetchPost() async {
    try {
      final respone = await http.get(Uri.parse(url));
      final jsonData = jsonDecode(respone.body) as List;

      setState(() {
        _postJson = jsonData;
      });
    } catch (err) {
      print(err);
    }
  }

  @override
  void initState() {
    super.initState();
    fetchPost();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("WIFI CONNECTIVITY"),
      ),
      body: ListView.builder(
        itemCount: _postJson.length,
        itemBuilder: (context, index) {
          final post = _postJson[index];
          return ListTile(
            leading: Text("Title: ${post["title"]}"),
          );
        },
      ),
    );
  }
}

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