Flutter中使用map函数触发NoSuchMethodError错误求助

报错信息 #

Exception has occurred.
NoSuchMethodError (NoSuchMethodError: The method 'map' was called on null. Receiver: null Tried calling: map(Closure: (String) => Answer))

问题代码 #

import 'package:flutter/material.dart';
import './question.dart';
import 'answer.dart';

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

class MyApp extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return MyAppState();
  }
}

class MyAppState extends State<MyApp> {
  var questionIndex = 0;
  void answerquestion() {
    setState(() {
      if (questionIndex < 1) {
        questionIndex = questionIndex + 1;
      }
    });

    print("answer question!");
  }

  @override
  Widget build(BuildContext context) {
    var questions = [
      {
        "questionText": "where are you from?",
        "answers": ["berlin ", "london", "DC", "new york"]
      },
      {
        "questionText": "what is your favourite color?",
        "answers": [" purple", "red", "yellow ", "blue"]
      }
    ];
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text("jini question"),
        ),
        body: Column(children: [
          Question(
            questions[questionIndex]["questionText"],
          ),
          ...(questions[questionIndex]["answer"] as List<String>).map((answer) {
            return Answer(answerquestion, answer);
          }).toList()
        ]),
      ),
    );
  }
}

解决方法 #

• 核心错误：键名拼写错误
  你在获取答案列表时使用了键名"answer"，但定义的questions数组里，存储答案的键是"answers"（复数形式）。这导致questions[questionIndex]["answer"]返回null，调用map方法时触发空指针异常。
  修正代码：将questions[questionIndex]["answer"]改为questions[questionIndex]["answers"]。

• 可选：添加空安全兜底
  为了避免后续类似的null问题，可以增加空检查，确保即使键不存在也不会崩溃：

  ...((questions[questionIndex]["answers"] as List<String>?) ?? []).map((answer) {
    return Answer(answerquestion, answer);
  }).toList()
  

内容的提问来源于stack exchange，提问作者base leader