如何创建在镖流？(How do you create a Stream in Dart?)

我基本上都知道如何使用它们; 例如收听元素的onclick流。

但是，你如何建立自己的俱乐部？

Answer 1:

简单的例子

下面是一个完整的工作示例：

import 'dart:async';
import 'dart:io';

class Application {
  Stream onExit;

  Application() {
    // Create a stream controller and assign its stream to "onExit".
    var controller = new StreamController();
    onExit = controller.stream;

    // Create some class that uses our stream.
    new UserOfStream(this);

    // Whenever we exit the application, notify everyone about it first.
    controller.add('we are shutting down!');
    exit(0);
  }
}

class UserOfStream {
  UserOfStream(app) {
    app.onExit.listen((String message) => print(message));
  }
}

main() => new Application();

你也可以做很酷的事情像检查是否有与用户controller.hasListener或者你可以发出一个错误信号。一定要检查的API文档StreamController 。

您可以使用new StreamController.broadcast()允许多个监听器。

对于复制pasters

这里有一个简单的方法来创建（用于复制pasters大片段）流：

class Something {
  StreamController _onExitController = new StreamController.broadcast();
  Stream get onExit => _onExitController.stream;
}

然后，类可以只访问_onExitController以控制流（对于实施例.add()

Answer 2:

我刚刚创建了一个新的飞镖库调用event_stream使你的类创建自定义的事件更容易。下面是一个例子：

class ClassWithEvents implements NotifyPropertyChanged {
  String _someProperty;

  final EventStream<PropertyChangedEventArgs> _onPropertyChangedEvent = new EventStream<PropertyChangedEventArgs>();
  Stream<PropertyChangedEventArgs> get onPropertyChanged => _onPropertyChangedEvent.stream;

  final EventStream _onClosedEvent = new EventStream();
  Stream get onClosed => _onClosedEvent.stream;

  String get someProperty => _someProperty;
  set someProperty(String value) {
    _onPropertyChangedEvent.signal(new PropertyChangedEventArgs('someProperty', value));
    _someProperty = value;
  }

  close() {
    _onClosedEvent.signal();
  }
}

main() {
  var c = new ClassWithEvents();
  c.onPropertyChanged.listen((PropertyChangedEventArgs<String> args) => print('changed: name=${args.propertyName} value=${args.value}'));
  c.onClosed.listen((_) => print('closed'));
  c.someProperty = "test";
  c.close();
}