Factor a Scrollable base class out of FixedHeightScrollable

sky/framework/components/fixed_height_scrollable.dart

Index: sky/framework/components/fixed_height_scrollable.dart
diff --git a/sky/framework/components/fixed_height_scrollable.dart b/sky/framework/components/fixed_height_scrollable.dart
index a3b789e78fbb7dadf236694d5055d2daa9da4015..fcb36da06c1763aa12e2261b34e21d582d93a913 100644
--- a/sky/framework/components/fixed_height_scrollable.dart
+++ b/sky/framework/components/fixed_height_scrollable.dart
@@ -2,11 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import '../animation/fling_curve.dart';
 import '../fn.dart';
 import 'dart:sky' as sky;
+import 'scrollable.dart';
 
-abstract class FixedHeightScrollable extends Component {
+abstract class FixedHeightScrollable extends Scrollable {
   // TODO(rafaelw): This component really shouldn't have an opinion
   // about how it is sized. The owning component should decide whether
   // it's explicitly sized or flexible or whatever...
@@ -22,29 +22,18 @@ abstract class FixedHeightScrollable extends Component {
     will-change: transform;'''
   );
 
-  double minOffset;
-  double maxOffset;
-
-  double _scrollOffset = 0.0;
-  FlingCurve _flingCurve;
-  int _flingAnimationId;
   double _height = 0.0;
   double _itemHeight;
 
   FixedHeightScrollable({
     Object key,
-    this.minOffset,
-    this.maxOffset
-  }) : super(key: key) {
-    events.listen('gestureflingstart', _handleFlingStart);
-    events.listen('gestureflingcancel', _handleFlingCancel);
-    events.listen('gesturescrollupdate', _handleScrollUpdate);
-    events.listen('wheel', _handleWheel);
+    double minOffset,
+    double maxOffset
+  }) : super(key: key, minOffset: minOffset, maxOffset: maxOffset) {
   }
 
-  List<Node> buildItems(int start, int count);
-
   void didMount() {
+    super.didMount();
     var root = getRoot();
     var item = root.firstChild.firstChild;
     sky.ClientRect scrollRect = root.getBoundingClientRect();
@@ -65,12 +54,12 @@ abstract class FixedHeightScrollable extends Component {
 
     if (_height > 0.0) {
       drawCount = (_height / _itemHeight).round() + 1;
-      double alignmentDelta = -_scrollOffset % _itemHeight;
+      double alignmentDelta = -scrollOffset % _itemHeight;
       if (alignmentDelta != 0.0) {
         alignmentDelta -= _itemHeight;
       }
 
-      double drawStart = _scrollOffset + alignmentDelta;
+      double drawStart = scrollOffset + alignmentDelta;
       itemNumber = (drawStart / _itemHeight).floor();
 
       transformStyle =
@@ -88,65 +77,4 @@ abstract class FixedHeightScrollable extends Component {
       ]
     );
   }
-
-  void didUnmount() {
-    _stopFling();
-  }
-
-  bool _scrollBy(double scrollDelta) {
-    var newScrollOffset = _scrollOffset + scrollDelta;
-    if (minOffset != null && newScrollOffset < minOffset) {
-      newScrollOffset = minOffset;
-    } else if (maxOffset != null && newScrollOffset > maxOffset) {
-      newScrollOffset = maxOffset;
-    }
-    if (newScrollOffset == _scrollOffset) {
-      return false;
-    }
-
-    setState(() {
-      _scrollOffset = newScrollOffset;
-    });
-    return true;
-  }
-
-  void _scheduleFlingUpdate() {
-    _flingAnimationId = sky.window.requestAnimationFrame(_updateFling);
-  }
-
-  void _stopFling() {
-    if (_flingAnimationId == null) {
-      return;
-    }
-
-    sky.window.cancelAnimationFrame(_flingAnimationId);
-    _flingCurve = null;
-    _flingAnimationId = null;
-  }
-
-  void _updateFling(double timeStamp) {
-    double scrollDelta = _flingCurve.update(timeStamp);
-    if (!_scrollBy(scrollDelta))
-      return _stopFling();
-    _scheduleFlingUpdate();
-  }
-
-  void _handleScrollUpdate(sky.GestureEvent event) {
-    _scrollBy(-event.dy);
-  }
-
-  void _handleFlingStart(sky.GestureEvent event) {
-    setState(() {
-      _flingCurve = new FlingCurve(-event.velocityY, event.timeStamp);
-      _scheduleFlingUpdate();
-    });
-  }
-
-  void _handleFlingCancel(sky.GestureEvent event) {
-    _stopFling();
-  }
-
-  void _handleWheel(sky.WheelEvent event) {
-    _scrollBy(-event.offsetY);
-  }
 }