dart - future 顺序

Question

在下面的代码中，我认为f1 > f2 > f3是调用顺序，但是仅f1被调用。如何获得依次调用的3个函数？

我已经将以下内容添加到main函数中，它可以按预期工作，但是我想知道是否还有其他确定的方法可以达到相同的结果？

print('Starting main');
List<Future> futures=new List<Future>();
Future v1=f1();
Future v2=f2();
Future v3=f3();
futures.add(v1);
futures.add(v2);
futures.add(v3);
Future.wait(futures);
print('Leaving main');

import 'dart:async';

Duration d1 = new Duration(seconds: 5);
Duration d2 = new Duration(seconds: 10);
Duration d3 = new Duration(seconds: 15);

bool r1 = false;
bool r2 = false;
bool r3 = false;

void cb1() {
    print('Entering CB1');
    r1 = true;
    print('Leaving CB1');
}

void cb2() {
    print('Entering CB2');
    r2 = true;
    print('Leaving CB2');
}

void cb3() {
    print('Entering CB3');
    r3 = true;
    print('Leaving CB3');
}

Timer t1;
Timer t2;
Timer t3;

Future<bool> start1() {
    print('Entering start1');
    Completer<bool> r = new Completer();
    r.future.then((_) {
        while (!r1) {

        }
        print('Completing start1');
        r.complete(true);
    });

    print('Leaving start1');
    return r.future;
}

Future<bool> start2() {
    print('Entering start2');
    Completer<bool> r = new Completer();
    r.future.then((_) {
        while (!r2) {

        }
        print('Completing start2');
        r.complete(true);
    });

    print('Leaving start2');
    return r.future;
}

Future<bool> start3() {
    print('Entering start3');
    Completer<bool> r = new Completer();
    r.future.then((_) {
        while (!r3) {

        }
        print('Completing start3');
        r.complete(true);
    });

    print('Leaving start3');
    return r.future;
}

Future<bool> f1() {
    print('Entering f1');
    Completer<bool> result = new Completer();
    t1 = new Timer(d1, cb1);
    result.complete(start1());

    print('Leaving f1');
    return result.future;
}

Future<bool> f2() {
    print('Entering f2');
    Completer<bool> result = new Completer();
    t2 = new Timer(d2, cb2);
    result.complete(start2());

    print('Leaving f2');
    return result.future;
}

Future<bool> f3() {
    print('Entering f3');
    Completer<bool> result = new Completer();
    t3 = new Timer(d3, cb3);
    result.complete(start3());

    print('Leaving f3');
    return result.future;
}

void main() {
    print('Starting main');
    f1().then((_) {
        f2().then((_) {
            f3().then((_) {

            });
        });
    });
    print('Leaving main');
}

Answer 1

首先，您应该阐明为什么需要此功能。我真的不明白为什么要让它们按顺序执行-您应该向我们提供更多有关其背后概念的信息。

请给我们更多有关您要完成的工作的信息!以下代码以某种方式做了我认为您想要的:

//我对代码做了更多清理:

import 'dart:async';

Duration d1 = new Duration(seconds: 5);
Duration d2 = new Duration(seconds: 10);
Duration d3 = new Duration(seconds: 15);

Future<bool> f1() {
  print('Entering f1');
  Completer<bool> r = new Completer();
  new Timer(d1, () {
    r.complete(true);
  });
  print('Leaving f1');
  return r.future;
}

Future<bool> f2() {
  print('Entering f2');
  Completer<bool> r = new Completer();
  new Timer(d2, () {
    r.complete(true);
  });
  print('Leaving f2');
  return r.future;
}

Future<bool> f3() {
  print('Entering f3');
  Completer<bool> r = new Completer();
  new Timer(d3, () {
    r.complete(true);
  });
  print('Leaving f3');
  return r.future;
}

void main() {
    print('Starting main');
    f1().then((_) {
        f2().then((_) {
            f3().then((_) {

            });
        });
    });
    print('Leaving main');
}