Change how events are handled in Effen

sky/framework/components/button_base.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import '../fn.dart';
 
 abstract class ButtonBase extends Component {
   bool highlight = false;
 
-  ButtonBase({ Object key }) : super(key: key) {
-    events.listen('pointerdown', _handlePointerDown);
-    events.listen('pointerup', _handlePointerUp);
-    events.listen('pointercancel', _handlePointerCancel);
+  ButtonBase({ Object key }) : super(key: key);
+
+  Node buildContent();

[rafaelw, 2015/03/19 06:11:26]

I'm tempted to feel like this is the wrong pattern, that we should be using
componentization rather than inheritance for composition. This way is more
compact, though. We can continue to see how it places out.

[abarth-chromium, 2015/03/19 14:19:59]

Yeah.

+
+  Node build() {
+    return new EventTarget(
+      buildContent(),
+      onPointerDown: _handlePointerDown,
+      onPointerUp: _handlePointerUp,
+      onPointerCancel: _handlePointerCancel
+    );
   }
 
   void _handlePointerDown(_) {
     setState(() {
       highlight = true;
     });
   }
   void _handlePointerUp(_) {
     setState(() {
       highlight = false;
     });
   }
   void _handlePointerCancel(_) {
     setState(() {
       highlight = false;
     });
   }
 }