Clarifying asynchronous operations in dart

Question

In the async codelab: Ref: https://dart.dev/codelabs/async-await

They have the following snippet:

Future<void> printOrderMessage() async {
  print('Awaiting user order...');
  var order = await fetchUserOrder();
  print('Your order is: $order');
}

Future<String> fetchUserOrder() {
  // Imagine that this function is more complex and slow.
  return Future.delayed(const Duration(seconds: 4), () => 'Large Latte');
}

void main() async {
  countSeconds(4);
  await printOrderMessage();
}

Based on the logic of printOrderMessage() I've made a similar function:

void main() async {
  int? value;
  value = await test();
  print(value);
}

Future<int?> test() async{
  print('Function has started');
  Future.delayed(Duration(milliseconds: 2000), () {
    return 4;
  });
}

In my case, it prints Function has started null. why doesn't it wait for the value to be populated

Because you don't return the inner future, so you await on nothing. return Future.delayed(Duration(milliseconds: 2000), () { <- add return first here — Per.J
– Per.J, Commented Oct 28, 2022 at 14:05

Fugipe · Accepted Answer · 2022-10-28 14:32:33Z

1

Future<int?> test() async {
  print('Function has started');
  await Future.delayed(Duration(milliseconds: 2000), () {});
  return 4;
}

Future<int?> test() async {
  print('Function has started');
  return Future.delayed(Duration(milliseconds: 2000), () {
return 4;
});
 
}

edited Oct 28, 2022 at 14:32

answered Oct 28, 2022 at 14:06

Fugipe

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1 Comment

Fugipe Over a year ago

you can remove "?" to int too

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