flutter - 如何在 Dart 中返回 Future<T> 结果

Question

我正在切换库，但我的界面是 getDuration返回 Duration由于引用过多，我无法更改此设置。
所以我必须返回Duration而不是 Future<Duration>在 AudioPlayer类(class)。
有什么办法吗？

这是解释我想要做什么的可执行代码。

import 'dart:core';
import 'dart:async';

// This interface is hardly to modify becase this is referenced from many place.
abstract class IAudioPlayer {
  Duration getDuration();
}

// This is old library that returns `Duration`
class OldLibraryAudioPlayer {
  Duration getDuration() {
    return Duration(seconds: 1);
  }
}

// This is new library that returns `Future<Duration>`
class NewLibraryAudioPlayer {
  Future<Duration> getDuration() async {
    var completer = new Completer<Duration>();

    new Timer(new Duration(seconds: 1),
        () => completer.complete(Duration(seconds: 1)));

    return completer.future;
  }
}

class AudioPlayer implements IAudioPlayer {
  // OldLibraryAudioPlayer _player = OldLibraryAudioPlayer();
  NewLibraryAudioPlayer _player = NewLibraryAudioPlayer();

  @override
  Duration getDuration() {
    // I want to return Duration instead of Future<Duration>.
    return _player.getDuration();
  }
}

void main() {
  final player = AudioPlayer();
  final duration = player.getDuration();
  print('$duration');
}

Answer 1

您需要将函数转换为 async或者直接返回结果。

例子:

Future<Duration> getDuration() async {
  final duration = await player.getDuration();
  return duration;
}

或者

Future<Duration> getDuration() {
  return player.getDuration();
}

希望有帮助!