Mark most State subclasses private

In the vast majority of cases, folks should be interacting with the Widget
rather than its State.

Fixes #267

sky/packages/sky/lib/src/widgets/animated_container.dart

@@ -77,10 +77,10 @@ class AnimatedContainer extends StatefulComponent {
   final Curve curve;
   final Duration duration;
 
-  AnimatedContainerState createState() => new AnimatedContainerState();
+  _AnimatedContainerState createState() => new _AnimatedContainerState();
 }
 
-class AnimatedContainerState extends State<AnimatedContainer> {
+class _AnimatedContainerState extends State<AnimatedContainer> {
   AnimatedBoxConstraintsValue _constraints;
   AnimatedBoxDecorationValue _decoration;
   AnimatedBoxDecorationValue _foregroundDecoration;

sky/packages/sky/lib/src/widgets/app.dart

@@ -38,7 +38,7 @@ class App extends StatefulComponent {
       'This might be a sign that you have not upgraded to our new Widgets framework.';
       'For more details see: https://groups.google.com/forum/#!topic/flutter-dev/hcX3OvLws9c';
       '...or look at our examples: https://github.com/flutter/engine/tree/master/examples';
-      return routes != null;      
+      return routes != null;
     });
   }
 
@@ -47,10 +47,10 @@ class App extends StatefulComponent {
   final Map<String, RouteBuilder> routes;
   final RouteGenerator onGenerateRoute;
 
-  AppState createState() => new AppState();
+  _AppState createState() => new _AppState();
 }
 
-class AppState extends State<App> {
+class _AppState extends State<App> {
 
   GlobalObjectKey _navigator;
 

sky/packages/sky/lib/src/widgets/basic.dart

@@ -808,10 +808,10 @@ class ImageListener extends StatefulComponent {
   final ImageFit fit;
   final ImageRepeat repeat;
 
-  ImageListenerState createState() => new ImageListenerState();
+  _ImageListenerState createState() => new _ImageListenerState();
 }
 
-class ImageListenerState extends State<ImageListener> {
+class _ImageListenerState extends State<ImageListener> {
   void initState() {
     super.initState();
     config.image.addListener(_handleImageChanged);

sky/packages/sky/lib/src/widgets/date_picker.dart

@@ -39,10 +39,10 @@ class DatePicker extends StatefulComponent {
   final DateTime firstDate;
   final DateTime lastDate;
 
-  DatePickerState createState() => new DatePickerState();
+  _DatePickerState createState() => new _DatePickerState();
 }
 
-class DatePickerState extends State<DatePicker> {
+class _DatePickerState extends State<DatePicker> {
   DatePickerMode _mode = DatePickerMode.day;
 
   void _handleModeChanged(DatePickerMode mode) {
@@ -70,7 +70,7 @@ class DatePickerState extends State<DatePicker> {
   static const double _calendarHeight = 210.0;
 
   Widget build(BuildContext context) {
-    Widget header = new DatePickerHeader(
+    Widget header = new _DatePickerHeader(
       selectedDate: config.selectedDate,
       mode: _mode,
       onModeChanged: _handleModeChanged
@@ -107,8 +107,8 @@ class DatePickerState extends State<DatePicker> {
 }
 
 // Shows the selected date in large font and toggles between year and day mode
-class DatePickerHeader extends StatelessComponent {
-  DatePickerHeader({ this.selectedDate, this.mode, this.onModeChanged }) {
+class _DatePickerHeader extends StatelessComponent {
+  _DatePickerHeader({ this.selectedDate, this.mode, this.onModeChanged }) {
     assert(selectedDate != null);
     assert(mode != null);
   }
@@ -290,10 +290,10 @@ class MonthPicker extends ScrollableWidgetList {
   final DateTime firstDate;
   final DateTime lastDate;
 
-  MonthPickerState createState() => new MonthPickerState();
+  _MonthPickerState createState() => new _MonthPickerState();
 }
 
-class MonthPickerState extends ScrollableWidgetListState<MonthPicker> {
+class _MonthPickerState extends ScrollableWidgetListState<MonthPicker> {
   void initState() {
     super.initState();
     _updateCurrentDate();
@@ -363,10 +363,10 @@ class YearPicker extends ScrollableWidgetList {
   final DateTime firstDate;
   final DateTime lastDate;
 
-  YearPickerState createState() => new YearPickerState();
+  _YearPickerState createState() => new _YearPickerState();
 }
 
-class YearPickerState extends ScrollableWidgetListState<YearPicker> {
+class _YearPickerState extends ScrollableWidgetListState<YearPicker> {
   int get itemCount => config.lastDate.year - config.firstDate.year + 1;
 
   List<Widget> buildItems(BuildContext context, int start, int count) {

sky/packages/sky/lib/src/widgets/dialog.dart

@@ -131,16 +131,15 @@ class Dialog extends StatelessComponent {
   }
 }
 
-const Duration _kTransitionDuration = const Duration(milliseconds: 150);
-
-class DialogRoute extends Route {
-  DialogRoute({ this.completer, this.builder });
+class _DialogRoute extends Route {
+  _DialogRoute({ this.completer, this.builder });
 
   final Completer completer;
   final RouteBuilder builder;
 
-  Duration get transitionDuration => _kTransitionDuration;
   bool get opaque => false;
+  Duration get transitionDuration => const Duration(milliseconds: 150);
+
   Widget build(NavigatorState navigator, PerformanceView nextRoutePerformance) {
     return new FadeTransition(
       performance: performance,
@@ -157,7 +156,7 @@ class DialogRoute extends Route {
 
 Future showDialog(NavigatorState navigator, DialogBuilder builder) {
   Completer completer = new Completer();
-  navigator.push(new DialogRoute(
+  navigator.push(new _DialogRoute(
     completer: completer,
     builder: (RouteArguments args) {
       return new Focus(

sky/packages/sky/lib/src/widgets/dismissable.dart

@@ -39,15 +39,15 @@ class Dismissable extends StatefulComponent {
     this.direction: DismissDirection.horizontal
   }) : super(key: key);
 
-  Widget child;
-  ResizedCallback onResized;
-  DismissedCallback onDismissed;
-  DismissDirection direction;
+  final Widget child;
+  final ResizedCallback onResized;
+  final DismissedCallback onDismissed;
+  final DismissDirection direction;
 
-  DismissableState createState() => new DismissableState();
+  _DismissableState createState() => new _DismissableState();
 }
 
-class DismissableState extends State<Dismissable> {
+class _DismissableState extends State<Dismissable> {
   void initState() {
     super.initState();
     _fadePerformance = new Performance(duration: _kCardDismissFadeout);

sky/packages/sky/lib/src/widgets/drag_target.dart

@@ -62,10 +62,10 @@ class Draggable extends StatefulComponent {
   final Offset feedbackOffset;
   final DragAnchor dragAnchor;
 
-  DraggableState createState() => new DraggableState();
+  _DraggableState createState() => new _DraggableState();
 }
 
-class DraggableState extends State<Draggable> {
+class _DraggableState extends State<Draggable> {
   DragRoute _route;
 
   void _startDrag(sky.PointerEvent event) {

sky/packages/sky/lib/src/widgets/drawer_item.dart

@@ -23,10 +23,10 @@ class DrawerItem extends StatefulComponent {
   final GestureTapCallback onPressed;
   final bool selected;
 
-  DrawerItemState createState() => new DrawerItemState();
+  _DrawerItemState createState() => new _DrawerItemState();
 }
 
-class DrawerItemState extends ButtonState<DrawerItem> {
+class _DrawerItemState extends ButtonState<DrawerItem> {
   TextStyle _getTextStyle(ThemeData themeData) {
     TextStyle result = themeData.text.body2;
     if (config.selected)

sky/packages/sky/lib/src/widgets/flat_button.dart

@@ -20,10 +20,10 @@ class FlatButton extends MaterialButton {
              enabled: enabled,
              onPressed: onPressed);
 
-  FlatButtonState createState() => new FlatButtonState();
+  _FlatButtonState createState() => new _FlatButtonState();
 }
 
-class FlatButtonState extends MaterialButtonState<FlatButton> {
+class _FlatButtonState extends MaterialButtonState<FlatButton> {
   Color getColor(BuildContext context) {
     if (!config.enabled || !highlight)
       return null;

sky/packages/sky/lib/src/widgets/floating_action_button.dart

@@ -27,10 +27,10 @@ class FloatingActionButton extends StatefulComponent {
   final Color backgroundColor;
   final GestureTapCallback onPressed;
 
-  FloatingActionButtonState createState() => new FloatingActionButtonState();
+  _FloatingActionButtonState createState() => new _FloatingActionButtonState();
 }
 
-class FloatingActionButtonState extends ButtonState<FloatingActionButton> {
+class _FloatingActionButtonState extends ButtonState<FloatingActionButton> {
   Widget buildContent(BuildContext context) {
     IconThemeColor iconThemeColor = IconThemeColor.white;
     Color materialColor = config.backgroundColor;

sky/packages/sky/lib/src/widgets/gesture_detector.dart

@@ -57,10 +57,10 @@ class GestureDetector extends StatefulComponent {
   final GestureScaleUpdateCallback onScaleUpdate;
   final GestureScaleEndCallback onScaleEnd;
 
-  GestureDetectorState createState() => new GestureDetectorState();
+  _GestureDetectorState createState() => new _GestureDetectorState();
 }
 
-class GestureDetectorState extends State<GestureDetector> {
+class _GestureDetectorState extends State<GestureDetector> {
   final PointerRouter _router = FlutterBinding.instance.pointerRouter;
 
   TapGestureRecognizer _tap;

sky/packages/sky/lib/src/widgets/homogeneous_viewport.dart

@@ -30,7 +30,7 @@ class HomogeneousViewport extends RenderObjectWidget {
   final ScrollDirection direction;
   final double startOffset;
 
-  HomogeneousViewportElement createElement() => new HomogeneousViewportElement(this);
+  _HomogeneousViewportElement createElement() => new _HomogeneousViewportElement(this);
 
   // we don't pass constructor arguments to the RenderBlockViewport() because until
   // we know our children, the constructor arguments we could give have no effect
@@ -48,8 +48,8 @@ class HomogeneousViewport extends RenderObjectWidget {
   // all the actual work is done in the element
 }
 
-class HomogeneousViewportElement extends RenderObjectElement<HomogeneousViewport> {
-  HomogeneousViewportElement(HomogeneousViewport widget) : super(widget);
+class _HomogeneousViewportElement extends RenderObjectElement<HomogeneousViewport> {
+  _HomogeneousViewportElement(HomogeneousViewport widget) : super(widget);
 
   List<Element> _children = const <Element>[];
   int _layoutFirstIndex;

sky/packages/sky/lib/src/widgets/icon.dart

@@ -61,7 +61,7 @@ class Icon extends StatelessComponent {
   final IconThemeColor color;
   final sky.ColorFilter colorFilter;
 
-  String getColorSuffix(BuildContext context) {
+  String _getColorSuffix(BuildContext context) {
     IconThemeColor iconThemeColor = color;
     if (iconThemeColor == null) {
       IconThemeData iconThemeData = IconTheme.of(context);
@@ -90,7 +90,7 @@ class Icon extends StatelessComponent {
     // TODO(eseidel): This clearly isn't correct.  Not sure what would be.
     // Should we use the ios images on ios?
     String density = 'drawable-xxhdpi';
-    String colorSuffix = getColorSuffix(context);
+    String colorSuffix = _getColorSuffix(context);
     return new AssetImage(
       bundle: _iconBundle,
       name: '${category}/${density}/ic_${subtype}_${colorSuffix}_${size}dp.png',

sky/packages/sky/lib/src/widgets/ink_well.dart

@@ -26,8 +26,8 @@ double _getSplashTargetSize(Size bounds, Point position) {
   return math.max(math.max(d1, d2), math.max(d3, d4)).ceil().toDouble();
 }
 
-class InkSplash {
-  InkSplash(this.position, this.well) {
+class _InkSplash {
+  _InkSplash(this.position, this.well) {
     _targetRadius = _getSplashTargetSize(well.size, position);
     _radius = new AnimatedValue<double>(
         _kSplashInitialSize, end: _targetRadius, curve: easeOut);
@@ -42,7 +42,7 @@ class InkSplash {
   }
 
   final Point position;
-  final RenderInkWell well;
+  final _RenderInkWell well;
 
   double _targetRadius;
   double _pinnedRadius;
@@ -98,8 +98,8 @@ class InkSplash {
   }
 }
 
-class RenderInkWell extends RenderProxyBox {
-  RenderInkWell({
+class _RenderInkWell extends RenderProxyBox {
+  _RenderInkWell({
     RenderBox child,
     GestureTapCallback onTap,
     GestureLongPressCallback onLongPress
@@ -122,7 +122,7 @@ class RenderInkWell extends RenderProxyBox {
     _syncLongPressRecognizer();
   }
 
-  final List<InkSplash> _splashes = new List<InkSplash>();
+  final List<_InkSplash> _splashes = new List<_InkSplash>();
 
   TapGestureRecognizer _tap;
   LongPressGestureRecognizer _longPress;
@@ -131,7 +131,7 @@ class RenderInkWell extends RenderProxyBox {
     if (event.type == 'pointerdown' && (_tap != null || _longPress != null)) {
       _tap?.addPointer(event);
       _longPress?.addPointer(event);
-      _splashes.add(new InkSplash(entry.localPosition, this));
+      _splashes.add(new _InkSplash(entry.localPosition, this));
     }
   }
 
@@ -196,7 +196,7 @@ class RenderInkWell extends RenderProxyBox {
       canvas.save();
       canvas.translate(offset.dx, offset.dy);
       canvas.clipRect(Point.origin & size);
-      for (InkSplash splash in _splashes)
+      for (_InkSplash splash in _splashes)
         splash.paint(canvas);
       canvas.restore();
     }
@@ -215,9 +215,9 @@ class InkWell extends OneChildRenderObjectWidget {
   final GestureTapCallback onTap;
   final GestureLongPressCallback onLongPress;
 
-  RenderInkWell createRenderObject() => new RenderInkWell(onTap: onTap, onLongPress: onLongPress);
+  _RenderInkWell createRenderObject() => new _RenderInkWell(onTap: onTap, onLongPress: onLongPress);
 
-  void updateRenderObject(RenderInkWell renderObject, InkWell oldWidget) {
+  void updateRenderObject(_RenderInkWell renderObject, InkWell oldWidget) {
     renderObject.onTap = onTap;
     renderObject.onLongPress = onLongPress;
   }

sky/packages/sky/lib/src/widgets/input.dart

@@ -39,10 +39,10 @@ class Input extends Scrollable {
   final String placeholder;
   final StringValueChanged onChanged;
 
-  InputState createState() => new InputState();
+  _InputState createState() => new _InputState();
 }
 
-class InputState extends ScrollableState<Input> {
+class _InputState extends ScrollableState<Input> {
   String _value;
   EditableString _editableValue;
   KeyboardHandle _keyboardHandle = KeyboardHandle.unattached;

sky/packages/sky/lib/src/widgets/material.dart

@@ -12,7 +12,7 @@ import 'package:sky/src/widgets/theme.dart';
 
 enum MaterialType { canvas, card, circle, button }
 
-const Map<MaterialType, double> edges = const {
+const Map<MaterialType, double> _kEdges = const <MaterialType, double>{
   MaterialType.canvas: null,
   MaterialType.card: 2.0,
   MaterialType.circle: null,
@@ -35,7 +35,7 @@ class Material extends StatelessComponent {
   final int level;
   final Color color;
 
-  Color getBackgroundColor(BuildContext context) {
+  Color _getBackgroundColor(BuildContext context) {
     if (color != null)
       return color;
     switch (type) {
@@ -55,10 +55,10 @@ class Material extends StatelessComponent {
         style: Theme.of(context).text.body1,
         child: contents
       );
-      if (edges[type] != null) {
+      if (_kEdges[type] != null) {
         contents = new ClipRRect(
-          xRadius: edges[type],
-          yRadius: edges[type],
+          xRadius: _kEdges[type],
+          yRadius: _kEdges[type],
           child: contents
         );
       }
@@ -69,8 +69,8 @@ class Material extends StatelessComponent {
         curve: ease,
         duration: const Duration(milliseconds: 200),
         decoration: new BoxDecoration(
-          backgroundColor: getBackgroundColor(context),
-          borderRadius: edges[type],
+          backgroundColor: _getBackgroundColor(context),
+          borderRadius: _kEdges[type],
           boxShadow: level == 0 ? null : shadows[level],
           shape: type == MaterialType.circle ? Shape.circle : Shape.rectangle
         ),

sky/packages/sky/lib/src/widgets/material_button.dart

@@ -9,7 +9,7 @@ import 'package:sky/src/widgets/framework.dart';
 import 'package:sky/src/widgets/ink_well.dart';
 import 'package:sky/src/widgets/material.dart';
 
-// Rather than using this class directly, please use FlatButton or RaisedButton.
+/// Rather than using this class directly, please use FlatButton or RaisedButton.
 abstract class MaterialButton extends StatefulComponent {
   MaterialButton({
     Key key,

sky/packages/sky/lib/src/widgets/mimic.dart

@@ -9,7 +9,7 @@ import 'package:sky/src/widgets/framework.dart';
 class MimicableKey {
   MimicableKey._(this._state);
 
-  final MimicableState _state;
+  final _MimicableState _state;
 
   Rect get globalBounds => _state._globalBounds;
 
@@ -35,10 +35,10 @@ class Mimicable extends StatefulComponent {
 
   final Widget child;
 
-  MimicableState createState() => new MimicableState();
+  _MimicableState createState() => new _MimicableState();
 }
 
-class MimicableState extends State<Mimicable> {
+class _MimicableState extends State<Mimicable> {
   Size _size;
   bool _beingMimicked = false;
 

sky/packages/sky/lib/src/widgets/mixed_viewport.dart

@@ -31,7 +31,7 @@ class MixedViewport extends RenderObjectWidget {
   final ExtentsUpdateCallback onExtentsUpdate;
   final InvalidatorAvailableCallback onInvalidatorAvailable;
 
-  MixedViewportElement createElement() => new MixedViewportElement(this);
+  _MixedViewportElement createElement() => new _MixedViewportElement(this);
 
   // we don't pass constructor arguments to the RenderBlockViewport() because until
   // we know our children, the constructor arguments we could give have no effect
@@ -60,8 +60,8 @@ class _ChildKey {
   String toString() => "_ChildKey(type: $type, key: $key)";
 }
 
-class MixedViewportElement extends RenderObjectElement<MixedViewport> {
-  MixedViewportElement(MixedViewport widget) : super(widget) {
+class _MixedViewportElement extends RenderObjectElement<MixedViewport> {
+  _MixedViewportElement(MixedViewport widget) : super(widget) {
     if (widget.onInvalidatorAvailable != null)
       widget.onInvalidatorAvailable(invalidate);
   }

sky/packages/sky/lib/src/widgets/popup_menu.dart

@@ -121,8 +121,8 @@ class MenuPosition {
   final double left;
 }
 
-class MenuRoute extends Route {
-  MenuRoute({ this.completer, this.position, this.builder, this.level });
+class _MenuRoute extends Route {
+  _MenuRoute({ this.completer, this.position, this.builder, this.level });
 
   final Completer completer;
   final MenuPosition position;
@@ -169,7 +169,7 @@ class MenuRoute extends Route {
 
 Future showMenu({ NavigatorState navigator, MenuPosition position, PopupMenuItemsBuilder builder, int level: 4 }) {
   Completer completer = new Completer();
-  navigator.push(new MenuRoute(
+  navigator.push(new _MenuRoute(
     completer: completer,
     position: position,
     builder: builder,