Dart tip of the day / Lecture 19 / Dart Completer

completer_turorial.dart

void main() async {
  print('시작');

  var result1 = await someDelayAsyncFunction();
  var result2 = await someDelayAsyncFunction();

  someDelayAsyncFunction().then((result ){

  });

  someDelayAsyncFunction().then((result ){

  });

  print(result1);

  multipleCallbackFunction((finalResult) {
    print(finalResult);
  });

}

Future<String> someDelayAsyncFunction([int delay = 2]) async {
  var completer = Completer();

  Future.delayed(Duration(seconds: delay), () {
    print('완료 $delay초 경과됨');
    completer.complete('완료 $delay초 경과됨');
    // completer.isCompleted
  });

  return await completer.future;
}

void someDelayCallbackFunction(
  void Function(String) callback, {
  int delay = 2,
}) {
  Future.delayed(Duration(seconds: delay), () {
    print('완료 $delay초 경과됨');
    callback('완료 $delay초 경과됨');
  });
}

void multipleCallbackFunction(void Function(List<String>) callback) {

  var firstCompleter = Completer<String>();
  var secondCompleter = Completer<String>();
  var thirdCompleter = Completer<String>();

  someDelayCallbackFunction(delay: 3, (result1) {
    firstCompleter.complete(result1);
  });

  someDelayCallbackFunction(delay: 1, (result2) {
    secondCompleter.complete(result2);
  });

  someDelayCallbackFunction(delay: 2, (result3) {
    thirdCompleter.complete(result3);
  });

  Future.wait([firstCompleter.future, secondCompleter.future, thirdCompleter.future])
      .then((results) {
        callback(results);
      });
}

Future<List<String>> multipleAsyncFunction() async {
  var firstCompleter = Completer<String>();
  var secondCompleter = Completer<String>();
  var thirdCompleter = Completer<String>();

  someDelayCallbackFunction(delay: 3, (result1) {
    firstCompleter.complete(result1);
  });

  someDelayCallbackFunction(delay: 1, (result2) {
    secondCompleter.complete(result2);
  });

  someDelayCallbackFunction(delay: 2, (result3) {
    thirdCompleter.complete(result3);
  });

  return Future.wait([firstCompleter.future, secondCompleter.future, thirdCompleter.future]);
}