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;
+  List<KeyboardEvent> _keyDownList = [];

[Anton Muhin, 2013/03/27 13:49:55]

that's not quite safe: it should be <KeyboardEvent>[], otherwise you loose
typechecks.

 
   /** 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(String type) :
+    _type = type, _target = null, super(_EVENT_TYPE) {

[Anton Muhin, 2013/03/27 13:49:55]

do you need explicit initliasation to null?  and why not this.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 = [];
+      EventTarget target) :
+    _type = type, _target = target, super(_EVENT_TYPE) {

[Anton Muhin, 2013/03/27 13:49:55]

ditto, this._type, this._target

     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 284 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);
 }