flutter await for condition to fulfill before continue with rest of code

Question

I need my async function to await for some expression to validate (ex. x == true) before continue with the rest of code.

right now I am using while loop like this

var x = false;

someFunction() async {

   // here I want to await for 
   // as long as it takes for x to become true

   while(!x) {
       await new Future.delayed(new Duration(milliseconds: 250));
   }

   // i put 250 millisecond intentional delay 
   // to protect process from blocking.
   // x is to be set true by external function
   // rest of code ...
}

await someFunction();

do you think there is a better way to wait for x to change to true before continue with execution ? Thank you

Answer 1

You could do something like this.

Future<void> _waitUntilDone() async {
    final completer = Completer();
    if (_loading) {
      await 200.milliseconds.delay();
      return _waitUntilDone();
    } else {
      completer.complete();
    }
    return completer.future;
  }

or even better

var completer;

Future<void> _waitUntilDone() async {
  completer = Completer();
  return completer.complete();
}

void done() {
  if (completer)
    completer.complete();
}

at complete call, we can also emit some value as well.

Answer 2

You can use three way to async/await :-

void method1(){
  List<String> myArray = <String>['a','b','c'];
  print('before loop');
  myArray.forEach((String value) async {
    await delayedPrint(value);
  });  
  print('end of loop');
}

void method2() async {
  List<String> myArray = <String>['a','b','c'];
  print('before loop');
  for(int i=0; i<myArray.length; i++) {
    await delayedPrint(myArray[i]);
  }
  print('end of loop');
}

Future<void> delayedPrint(String value) async {
  await Future.delayed(Duration(seconds: 1));
  print('delayedPrint: $value');
}