KeyboardEventStream: lock it down

tools/dom/src/KeyboardEventStream.dart

 // Copyright (c) 2012, 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;
 
 /**
  * Internal class that does the actual calculations to determine keyCode and
  * charCode for keydown, keypress, and keyup events for all browsers.
  */
-class _KeyboardEventHandler implements EventStreamProvider<KeyEvent> {
+class _KeyboardEventHandler extends EventStreamProvider<KeyEvent> {
   // This code inspired by Closure's KeyHandling library.
   // http://closure-library.googlecode.com/svn/docs/closure_goog_events_keyhandler.js.source.html
 
   /**
    * The set of keys that have been pressed down without seeing their
    * corresponding keyup event.
    */
-  List<KeyboardEvent> _keyDownList;
-
-  /** The set of functions that wish to be notified when a KeyEvent happens. */
-  List<Function> _callbacks;
+  final List<KeyboardEvent> _keyDownList = <KeyboardEvent>[];
 
   /** The type of KeyEvent we are tracking (keyup, keydown, keypress). */
-  String _type;
+  final String _type;
 
   /** The element we are watching for events to happen on. */
-  EventTarget _target;
+  final EventTarget _target;
 
   // The distance to shift from upper case alphabet Roman letters to lower case.
-  final int _ROMAN_ALPHABET_OFFSET = "a".codeUnits[0] - "A".codeUnits[0];
+  static final int _ROMAN_ALPHABET_OFFSET = "a".codeUnits[0] - "A".codeUnits[0];
 
   /** Controller to produce KeyEvents for the stream. */
-  StreamController _controller;
+  final StreamController _controller = new StreamController.broadcast();
 
-  String _eventType = 'KeyEvent';
+  static const _EVENT_TYPE = 'KeyEvent';
 
   /**
    * An enumeration of key identifiers currently part of the W3C draft for DOM3
    * and their mappings to keyCodes.
    * http://www.w3.org/TR/DOM-Level-3-Events/keyset.html#KeySet-Set
    */
-  static Map<String, int> _keyIdentifier = {
+  static const Map<String, int> _keyIdentifier = const {
     'Up': KeyCode.UP,
     'Down': KeyCode.DOWN,
     'Left': KeyCode.LEFT,
     'Right': KeyCode.RIGHT,
     'Enter': KeyCode.ENTER,
     'F1': KeyCode.F1,
     'F2': KeyCode.F2,
     'F3': KeyCode.F3,
     'F4': KeyCode.F4,
     'F5': KeyCode.F5,
     'F6': KeyCode.F6,
     'F7': KeyCode.F7,
     'F8': KeyCode.F8,
     'F9': KeyCode.F9,
     'F10': KeyCode.F10,
     'F11': KeyCode.F11,
     'F12': KeyCode.F12,
     'U+007F': KeyCode.DELETE,
     'Home': KeyCode.HOME,
     'End': KeyCode.END,
     'PageUp': KeyCode.PAGE_UP,
     'PageDown': KeyCode.PAGE_DOWN,
     'Insert': KeyCode.INSERT
   };
 
-  /**
-   * Gets the type of the event which this would listen for on the specified
-   * event target.
-   */
-  String getEventType(EventTarget target) => _eventType;
-
   /** Return a stream for KeyEvents for the specified target. */
   Stream<KeyEvent> forTarget(EventTarget e, {bool useCapture: false}) {
     return new _KeyboardEventHandler.initializeAllEventListeners(
         _type, e).stream;
   }
 
   /**
    * Accessor to the stream associated with a particular KeyboardEvent
    * EventTarget.
    *
    * [forTarget] must be called to initialize this stream to listen to a
    * particular EventTarget.
    */
   Stream<KeyEvent> get stream {
     if(_target != null) {
       return _controller.stream;
     } else {
       throw new StateError("Not initialized. Call forTarget to access a stream "
           "initialized with a particular EventTarget.");
     }
   }
 
   /**
    * General constructor, performs basic initialization for our improved
    * KeyboardEvent controller.
    */
-  _KeyboardEventHandler(String type) {
-    _commonInit(type);
-  }
-
-  void _commonInit(String type) {
-    _type = type;
-    _controller = new StreamController.broadcast();
-    _callbacks = [];
-    _target = null;
+  _KeyboardEventHandler(this._type) :
+    _target = null, super(_EVENT_TYPE) {
   }
 
   /**
    * Hook up all event listeners under the covers so we can estimate keycodes
    * and charcodes when they are not provided.
    */
-  _KeyboardEventHandler.initializeAllEventListeners(String type,
-      EventTarget target) {
-    _commonInit(type);
-    _target = target;
-    _keyDownList = [];
+  _KeyboardEventHandler.initializeAllEventListeners(this._type, this._target) : 
+    super(_EVENT_TYPE) {
     Element.keyDownEvent.forTarget(_target, useCapture: true).listen(
         processKeyDown);
     Element.keyPressEvent.forTarget(_target, useCapture: true).listen(
         processKeyPress);
     Element.keyUpEvent.forTarget(_target, useCapture: true).listen(
         processKeyUp);
   }
 
   /**
    * Notify all callback listeners that a KeyEvent of the relevant type has
@@ skipping 182 matching lines @@
   /** Handle keydown events. */
   void processKeyDown(KeyboardEvent e) {
     // Ctrl-Tab and Alt-Tab can cause the focus to be moved to another window
     // before we've caught a key-up event.  If the last-key was one of these
     // we reset the state.
     if (_keyDownList.length > 0 &&
         (_keyDownList.last.keyCode == KeyCode.CTRL && !e.ctrlKey ||
          _keyDownList.last.keyCode == KeyCode.ALT && !e.altKey ||
          Device.userAgent.contains('Mac') &&
          _keyDownList.last.keyCode == KeyCode.META && !e.metaKey)) {
-      _keyDownList = [];
+      _keyDownList.clear();
     }
 
     var event = new KeyEvent(e);
     event._shadowKeyCode = _normalizeKeyCodes(event);
     // Technically a "keydown" event doesn't have a charCode. This is
     // calculated nonetheless to provide us with more information in giving
     // as much information as possible on keypress about keycode and also
     // charCode.
     event._shadowCharCode = _findCharCodeKeyDown(event);
     if (_keyDownList.length > 0 && event.keyCode != _keyDownList.last.keyCode &&
@@ skipping 39 matching lines @@
   /** Handle keyup events. */
   void processKeyUp(KeyboardEvent event) {
     var e = new KeyEvent(event);
     KeyboardEvent toRemove = null;
     for (var key in _keyDownList) {
       if (key.keyCode == e.keyCode) {
         toRemove = key;
       }
     }
     if (toRemove != null) {
-      _keyDownList =
-          _keyDownList.where((element) => element != toRemove).toList();
+      _keyDownList.removeWhere((element) => element == toRemove);
     } else if (_keyDownList.length > 0) {
       // This happens when we've reached some international keyboard case we
       // haven't accounted for or we haven't correctly eliminated all browser
       // inconsistencies. Filing bugs on when this is reached is welcome!
       _keyDownList.removeLast();
     }
     _dispatch(e);
   }
 }
 
@@ skipping 20 matching lines @@
       new _KeyboardEventHandler('keypress').forTarget(target);
 
   /** Named constructor to produce a stream for onKeyUp events. */
   static Stream<KeyEvent> onKeyUp(EventTarget target) =>
       new _KeyboardEventHandler('keyup').forTarget(target);
 
   /** Named constructor to produce a stream for onKeyDown events. */
   static Stream<KeyEvent> onKeyDown(EventTarget target) =>
     new _KeyboardEventHandler('keydown').forTarget(target);
 }