如何解决Dart中“参数类型Object?不能分配给参数类型String”报错

• 字段名大小写不匹配：定义的答案分数字段为小写score，代码取值时写为大写Score，字段不匹配会导致取值为空
• 类型未明确转换：你将answers的Map泛型声明为Map<String, Object>，从Map中取出的值默认是Object?可空对象类型，无法直接赋值给要求String类型的参数

快速修复 #

先修正字段大小写，再对取出的值做显式类型转换，修改后的代码如下：

Question(question[questionindex]['questionText'] as String),
...(question[questionindex]['answers'] as List<Map<String,Object>>).map((answer) {
  return Answer(() => answerQuestion(answer['score'] as String), answer['text'] as String);
}).toList(),

如果要兼容空值避免运行时报错，可以增加空安全 fallback 逻辑：

Question(question[questionindex]['questionText'] ?? '默认问题'),
...(question[questionindex]['answers'] as List<Map<String,Object>>).map((answer) {
  final score = answer['score'] as String? ?? '0';
  final text = answer['text'] as String? ?? '默认选项';
  return Answer(() => answerQuestion(score), text);
}).toList(),

规范优化方案 #

推荐为数据定义实体类，从根源避免类型匹配问题，代码可维护性更高：

// 定义实体类
class QuestionItem {
  final String questionText;
  final List<AnswerItem> answers;

  QuestionItem({required this.questionText, required this.answers});
}

class AnswerItem {
  final String text;
  final String score;

  AnswerItem({required this.text, required this.score});
}

// 初始化数据
final _question = [
  QuestionItem(
    questionText: "what's your favourite color?",
    answers: [
      AnswerItem(text: 'Black', score: '10'),
      AnswerItem(text: 'Green', score: '80'),
      AnswerItem(text: 'Blue', score: '147'),
      AnswerItem(text: 'Yellow', score: '60'),
    ],
  ),
  QuestionItem(
    questionText: "what's your favourite animal?",
    answers: [
      AnswerItem(text: 'Rabbit', score: '10'),
      AnswerItem(text: 'Tiger', score: '10'),
      AnswerItem(text: 'Elephant', score: '10'),
      AnswerItem(text: 'Lion', score: '10'),
    ],
  ),
];

// 调用代码，无需类型转换
Question(_question[questionindex].questionText),
..._question[questionindex].answers.map((answer) {
  return Answer(() => answerQuestion(answer.score), answer.text);
}).toList(),

内容的提问来源于stack exchange，提问作者ingmbk