Flutter Await not waiting

Question

Why won't the program wait for the function to return the list before going to the print statement?

I think it's because I made the forEach loop async but I need it to be async to get the newSummary which is a 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();
}

score 2 · Answer 1 · answered Jul 04 '20 at 22:02

Please replace the following

  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);
  });

with this

  await Future.wait(  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);
  }));

This works too! But changing the forEach to a for loop also worked and was a bit shorter. — 123432198765, Jul 04 '20 at 22:06
Using this exact code thrown this error: 'This expression has a type of 'void' so its value can't be used.' for `forEach` of a `List`. — mrahimygk, Jan 18 '21 at 17:25

JideGuru · Accepted Answer · 2020-07-04T21:52:39.813

1

You're executing your return [{'hi':5}] in a callback which wouldn't work. You should await the Future.delayed then return the List like this await Future.delayed(Duration(seconds: 2));.

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();
}

edited Jul 04 '20 at 21:52

answered Jul 04 '20 at 21:49

JideGuru

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Yup sorry this was just a minimum reproducible example and I made a mistake. Let me edit the post and add the actual code – 123432198765 Jul 04 '20 at 21:52
Okay sure. i'll be waiting – JideGuru Jul 04 '20 at 21:52
Did you try using `For` loop instead of forEach? – JideGuru Jul 04 '20 at 22:00

Flutter Await not waiting

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