为什么我会收到“类型‘List<dynamic>’不是类型‘List<DocumentReference<Map<String, dynamic>>>’的子类型”错误？

Question

我在 flutter 中运行单元测试，出现错误： 类型“List”不是类型“List>>”

的子类型

相关代码片段如下，我试图从 firebase 读取数据。

 factory TimerSessionModel.fromSnapshot(
      DocumentSnapshot<Map<String, dynamic>> snapshot) {
    final data = snapshot.data()!;
    return TimerSessionModel(
      selfRef: snapshot.reference,
      activeExecutionRef: data['activeExecutionRef'],
      autoStartNextTimer: data['autoStartNextTimer'] as bool,
      ownerRef: data['ownerRef'],
      timerRefs: data['timerRefs'],
      title: data['title'] as String,
    );
  }

这里timerRefs是一个文档引用列表，问题所指向的地方。

我尝试运行单元测试并给出了如上所述的错误

Answer 1

您需要将列表类型转换为 >>。

    factory TimerSessionModel.fromSnapshot(
  DocumentSnapshot<Map<String, dynamic>> snapshot) {
  final data = snapshot.data()!;
  // Convert List<dynamic> to List<DocumentReference<Map<String, dynamic>>>
  List<DocumentReference<Map<String, dynamic>>> timerRefs = 
    (data['timerRefs'] as List<dynamic>)
    .map((ref) => ref as DocumentReference<Map<String, dynamic>>)
    .toList();

  return TimerSessionModel(
    selfRef: snapshot.reference,
    activeExecutionRef: data['activeExecutionRef'],
    autoStartNextTimer: data['autoStartNextTimer'] as bool,
    ownerRef: data['ownerRef'],
    timerRefs: timerRefs,
    title: data['title'] as String,
  );
}