flutter - Flutter Await不等待

Question

为什么程序在进入打印语句之前不等待函数返回列表？
我认为这是因为我使forEach循环异步，但我需要使其异步才能获得newSummary，这是一个Future。

Future syncToCloud() async{
  final List<Map<String,dynamic>> _events = await events();
  print(_events.length);
}
  
  
Future<List<Map<String, dynamic>>> events() async {
  List<Map<String, dynamic>> maps = await db.query('data');
  List<Map<String, dynamic>> newMaps=[];

  maps.forEach((element)async{
    Map<String, dynamic> newElement = {};

    if(element['summary']!=''){
      newElement['summary'] = await newSummary(element['summary']);
      print(newElement['summary']);
    }
    else{
      newElement['summary'] = element['summary'];
    }
    newMaps.add(newElement);
  });
  
    return newMaps;
}
  

void main()async{
  await syncToCloud();
}

Answer 1

您正在无法执行的回调中执行return [{'hi':5}]。您应该等待Future.delayed，然后像await Future.delayed(Duration(seconds: 2));这样返回List。

Future syncToCloud() async{
  final List<Map<String,dynamic>> _events = await events();
  print(_events.length);
}
  
  
Future<List<Map<String, dynamic>>> events() async {
  await Future.delayed(Duration(seconds: 2));
  return [{'hi':5}];
}
  

void main()async{
  await syncToCloud();
}