Switching DOM events over to using StreamController.

tools/dom/src/EventStreamProvider.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of html;
 
-/**
- * Adapter for exposing DOM events as Dart streams.
- */
-class _EventStream<T extends Event> extends Stream<T> {
-  final EventTarget _target;
-  final String _eventType;
-  final bool _useCapture;
-
-  _EventStream(this._target, this._eventType, this._useCapture);
-
-  // DOM events are inherently multi-subscribers.
-  Stream<T> asBroadcastStream() => this;
-  bool get isBroadcast => true;
-
-  StreamSubscription<T> listen(void onData(T event),
-      { void onError(error),
-        void onDone(),
-        bool cancelOnError}) {
-
-    return new _EventStreamSubscription<T>(
-        this._target, this._eventType, onData, this._useCapture);
-  }
-}
-
-class _EventStreamSubscription<T extends Event> extends StreamSubscription<T> {
-  int _pauseCount = 0;
-  EventTarget _target;
-  final String _eventType;
-  var _onData;
-  final bool _useCapture;
-
-  _EventStreamSubscription(this._target, this._eventType, this._onData,
-      this._useCapture) {
-    _tryResume();
-  }
-
-  void cancel() {
-    if (_canceled) return;
-
-    _unlisten();
-    // Clear out the target to indicate this is complete.
-    _target = null;
-    _onData = null;
-  }
-
-  bool get _canceled => _target == null;
-
-  void onData(void handleData(T event)) {
-    if (_canceled) {
-      throw new StateError("Subscription has been canceled.");
-    }
-    // Remove current event listener.
-    _unlisten();
-
-    _onData = handleData;
-    _tryResume();
-  }
-
-  /// Has no effect.
-  void onError(void handleError(error)) {}
-
-  /// Has no effect.
-  void onDone(void handleDone()) {}
-
-  void pause([Future resumeSignal]) {
-    if (_canceled) return;
-    ++_pauseCount;
-    _unlisten();
-
-    if (resumeSignal != null) {
-      resumeSignal.whenComplete(resume);
-    }
-  }
-
-  bool get isPaused => _pauseCount > 0;
-
-  void resume() {
-    if (_canceled || !isPaused) return;
-    --_pauseCount;
-    _tryResume();
-  }
-
-  void _tryResume() {
-    if (_onData != null && !isPaused) {
-      _target.$dom_addEventListener(_eventType, _onData, _useCapture);
-    }
-  }
-
-  void _unlisten() {
-    if (_onData != null) {
-      _target.$dom_removeEventListener(_eventType, _onData, _useCapture);
-    }
-  }
-
-  Future asFuture([var futureValue]) {
-    // We just need a future that will never succeed or fail.
-    Completer completer = new Completer();
-    return completer.future;
-  }
-}
-
 
 /**
  * A factory to expose DOM events as Streams.
  */
 class EventStreamProvider<T extends Event> {
   final String _eventType;
 
   const EventStreamProvider(this._eventType);
 
   /**
    * Gets a [Stream] for this event type, on the specified target.
    *
    * This will always return a broadcast stream so multiple listeners can be
    * used simultaneously.
    *
    * This may be used to capture DOM events:
    *
    *     Element.keyDownEvent.forTarget(element, useCapture: true).listen(...);
    *
    * Or for listening to an event which will bubble through the DOM tree:
    *
    *     MediaElement.pauseEvent.forTarget(document.body).listen(...);
    *
    * See also:
    *
    * [addEventListener](http://docs.webplatform.org/wiki/dom/methods/addEventListener)
    */
   Stream<T> forTarget(EventTarget e, {bool useCapture: false}) {
-    return new _EventStream(e, _eventType, useCapture);
+    var controller;
+
+    void onData(data) {
+      controller.add(data);
+    }
+
+    controller = new StreamController<T>(
+        onListen: () {
+          e.$dom_addEventListener(_eventType, onData, useCapture);
+        },
+        onCancel: () {
+          e.$dom_removeEventListener(_eventType, onData, useCapture);
+        },
+        sync: true);
+
+    return controller.stream;
   }
 
   /**
    * Gets the type of the event which this would listen for on the specified
    * event target.
    *
    * The target is necessary because some browsers may use different event names
    * for the same purpose and the target allows differentiating browser support.
    */
   String getEventType(EventTarget target) {
     return _eventType;
   }
 }
 
 /**
  * A factory to expose DOM events as streams, where the DOM event name has to
  * be determined on the fly (for example, mouse wheel events).
  */
 class _CustomEventStreamProvider<T extends Event>
     implements EventStreamProvider<T> {
 
   final _eventTypeGetter;
   const _CustomEventStreamProvider(this._eventTypeGetter);
 
   Stream<T> forTarget(EventTarget e, {bool useCapture: false}) {
-    return new _EventStream(e, _eventTypeGetter(e), useCapture);
+    var controller;
+
+    var eventType = _eventTypeGetter(e);
+
+    void onData(data) {
+      controller.add(data);
+    }
+
+    controller = new StreamController<T>(
+        onListen: () {
+          e.$dom_addEventListener(eventType, onData, useCapture);
+        },
+        onCancel: () {
+          e.$dom_removeEventListener(eventType, onData, useCapture);
+        },
+        sync: true);
+
+    return controller.stream;
   }
 
   String getEventType(EventTarget target) {
     return _eventTypeGetter(target);
   }
 }