Add an initial implementation of Navigator2

This navigator can handle simple page navigation. I'll add more features in
subsequent CLs.

examples/widgets/navigation.dart

@@ -4,51 +4,71 @@
 
 import 'package:flutter/material.dart';
 
+import 'package:flutter/src/widgets/navigator2.dart' as n2;
+
+class Home extends StatelessComponent {
+  Widget build(BuildContext context) {
+    return new Container(
+      padding: const EdgeDims.all(30.0),
+      decoration: new BoxDecoration(backgroundColor: const Color(0xFFCCCCCC)),
+      child: new Column(<Widget>[
+        new Text("You are at home"),
+        new RaisedButton(
+          child: new Text('GO SHOPPING'),
+          onPressed: () => n2.Navigator.of(context).pushNamed('/shopping')
+        ),
+        new RaisedButton(
+          child: new Text('START ADVENTURE'),
+          onPressed: () => n2.Navigator.of(context).pushNamed('/adventure')
+        )],
+        justifyContent: FlexJustifyContent.center
+      )
+    );
+  }
+}
+
+class Shopping extends StatelessComponent {
+  Widget build(BuildContext context) {
+    return new Container(
+      padding: const EdgeDims.all(20.0),
+      decoration: new BoxDecoration(backgroundColor: const Color(0xFFBF5FFF)),
+      child: new Column(<Widget>[
+        new Text("Village Shop"),
+        new RaisedButton(
+          child: new Text('RETURN HOME'),
+          onPressed: () => n2.Navigator.of(context).pop()
+        ),
+        new RaisedButton(
+          child: new Text('GO TO DUNGEON'),
+          onPressed: () => n2.Navigator.of(context).pushNamed('/adventure')
+        )],
+        justifyContent: FlexJustifyContent.center
+      )
+    );
+  }
+}
+
+class Adventure extends StatelessComponent {
+  Widget build(BuildContext context) {
+    return new Container(
+      padding: const EdgeDims.all(20.0),
+      decoration: new BoxDecoration(backgroundColor: const Color(0xFFDC143C)),
+      child: new Column(<Widget>[
+        new Text("Monster's Lair"),
+        new RaisedButton(
+          child: new Text('RUN!!!'),
+          onPressed: () => n2.Navigator.of(context).pop()
+        )],
+        justifyContent: FlexJustifyContent.center
+      )
+    );
+  }
+}
+
 final Map<String, RouteBuilder> routes = <String, RouteBuilder>{
-  '/': (RouteArguments args) => new Container(
-    padding: const EdgeDims.all(30.0),
-    decoration: new BoxDecoration(backgroundColor: const Color(0xFFCCCCCC)),
-    child: new Column(<Widget>[
-      new Text("You are at home"),
-      new RaisedButton(
-        child: new Text('GO SHOPPING'),
-        onPressed: () => Navigator.of(args.context).pushNamed('/shopping')
-      ),
-      new RaisedButton(
-        child: new Text('START ADVENTURE'),
-        onPressed: () => Navigator.of(args.context).pushNamed('/adventure')
-      )],
-      justifyContent: FlexJustifyContent.center
-    )
-  ),
-  '/shopping': (RouteArguments args) => new Container(
-    padding: const EdgeDims.all(20.0),
-    decoration: new BoxDecoration(backgroundColor: const Color(0xFFBF5FFF)),
-    child: new Column(<Widget>[
-      new Text("Village Shop"),
-      new RaisedButton(
-        child: new Text('RETURN HOME'),
-        onPressed: () => Navigator.of(args.context).pop()
-      ),
-      new RaisedButton(
-        child: new Text('GO TO DUNGEON'),
-        onPressed: () => Navigator.of(args.context).pushNamed('/adventure')
-      )],
-      justifyContent: FlexJustifyContent.center
-    )
-  ),
-  '/adventure': (RouteArguments args) => new Container(
-    padding: const EdgeDims.all(20.0),
-    decoration: new BoxDecoration(backgroundColor: const Color(0xFFDC143C)),
-    child: new Column(<Widget>[
-      new Text("Monster's Lair"),
-      new RaisedButton(
-        child: new Text('RUN!!!'),
-        onPressed: () => Navigator.of(args.context).pop()
-      )],
-      justifyContent: FlexJustifyContent.center
-    )
-  )
+  '/': (_) => new Home(),
+  '/shopping': (_) => new Shopping(),
+  '/adventure': (_) => new Adventure(),
 };
 
 final ThemeData theme = new ThemeData(

packages/flutter/lib/src/material/material_app.dart

@@ -8,6 +8,8 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
 
+import 'package:flutter/src/widgets/navigator2.dart' as n2;
+
 import 'theme.dart';
 import 'title.dart';
 
@@ -31,6 +33,8 @@ AssetBundle _initDefaultBundle() {
 
 final AssetBundle _defaultBundle = _initDefaultBundle();
 
+const bool _kUseNavigator2 = false;
+
 class MaterialApp extends StatefulComponent {
   MaterialApp({
     Key key,
@@ -83,6 +87,19 @@ class _MaterialAppState extends State<MaterialApp> {
   void _metricHandler(Size size) => setState(() { _size = size; });
 
   Widget build(BuildContext context) {
+    Widget navigator;
+    if (_kUseNavigator2) {
+      navigator = new n2.Navigator(
+        key: _navigator,
+        routes: config.routes
+      );
+    } else {
+      navigator = new Navigator(
+        key: _navigator,
+        routes: config.routes,
+        onGenerateRoute: config.onGenerateRoute
+      );
+    }
     return new MediaQuery(
       data: new MediaQueryData(size: _size),
       child: new Theme(
@@ -93,11 +110,7 @@ class _MaterialAppState extends State<MaterialApp> {
             bundle: _defaultBundle,
             child: new Title(
               title: config.title,
-              child: new Navigator(
-                key: _navigator,
-                routes: config.routes,
-                onGenerateRoute: config.onGenerateRoute
-              )
+              child: navigator
             )
           )
         )

packages/flutter/lib/src/widgets/navigator2.dart

@@ -0,0 +1,206 @@
+// 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 'dart:async';
+
+import 'package:flutter/animation.dart';
+
+import 'basic.dart';
+import 'framework.dart';
+import 'overlay.dart';
+import 'transitions.dart';
+
+abstract class Route {
+  /// Override this function to return the widget that this route should display.
+  Widget createWidget();
+
+  Widget _child;
+  OverlayEntry _entry;
+
+  void willPush() {
+    _child = createWidget();
+  }
+
+  void didPop(dynamic result) {
+    _entry.remove();
+  }
+}
+
+typedef Widget RouteBuilder(args);
+typedef RouteBuilder RouteGenerator(String name);
+
+const String _kDefaultPageName = '/';
+
+class Navigator extends StatefulComponent {
+  Navigator({
+    Key key,
+    this.routes,
+    this.onGeneratePage,
+    this.onUnknownPage
+  }) : super(key: key) {
+    // To use a navigator, you must at a minimum define the route with the name '/'.
+    assert(routes != null);
+    assert(routes.containsKey(_kDefaultPageName));
+  }
+
+  final Map<String, RouteBuilder> routes;
+
+  /// you need to implement this if you pushNamed() to names that might not be in routes.
+  final RouteGenerator onGeneratePage;
+
+  /// 404 generator. You only need to implement this if you have a way to navigate to arbitrary names.
+  final RouteBuilder onUnknownPage;
+
+  static NavigatorState of(BuildContext context) {
+    NavigatorState result;
+    context.visitAncestorElements((Element element) {
+      if (element is StatefulComponentElement && element.state is NavigatorState) {
+        result = element.state;
+        return false;
+      }
+      return true;
+    });
+    return result;
+  }
+
+  NavigatorState createState() => new NavigatorState();
+}
+
+class NavigatorState extends State<Navigator> {
+  GlobalKey<OverlayState> _overlay = new GlobalKey<OverlayState>();
+  List<Route> _history = new List<Route>();
+
+  void initState() {
+    super.initState();
+    _addRouteToHistory(new PageRoute(
+      builder: config.routes[_kDefaultPageName],
+      name: _kDefaultPageName
+    ));
+  }
+
+  RouteBuilder _generatePage(String name) {
+    assert(config.onGeneratePage != null);
+    return config.onGeneratePage(name);
+  }
+
+  bool get hasPreviousRoute => _history.length > 1;
+
+  void pushNamed(String name, { Set<Key> mostValuableKeys }) {
+    final RouteBuilder builder = config.routes[name] ?? _generatePage(name) ?? config.onUnknownPage;
+    assert(builder != null); // 404 getting your 404!
+    push(new PageRoute(
+      builder: builder,
+      name: name,
+      mostValuableKeys: mostValuableKeys
+    ));
+  }
+
+  void _addRouteToHistory(Route route) {
+    route.willPush();
+    route._entry = new OverlayEntry(child: route._child);
+    _history.add(route);
+  }
+
+  void push(Route route) {
+    OverlayEntry reference = _history.last._entry;
+    _addRouteToHistory(route);
+    _overlay.currentState.insert(route._entry, above: reference);
+  }
+
+  void pop([dynamic result]) {
+    _history.removeLast().didPop(result);
+  }
+
+  Widget build(BuildContext context) {
+    return new Overlay(
+      key: _overlay,
+      initialEntries: <OverlayEntry>[ _history.first._entry ]
+    );
+  }
+}
+
+abstract class TransitionRoute extends Route {
+  PerformanceView get performance => _performance?.view;
+  Performance _performance;
+
+  Duration get transitionDuration;
+
+  Performance createPerformance() {
+    Duration duration = transitionDuration;
+    assert(duration != null && duration >= Duration.ZERO);
+    return new Performance(duration: duration, debugLabel: debugLabel);
+  }
+
+  void willPush() {
+    _performance = createPerformance();
+    _performance.forward();
+    super.willPush();
+  }
+
+  Future didPop(dynamic result) async {
+    await _performance.reverse();
+    super.didPop(result);
+  }
+
+  String get debugLabel => '$runtimeType';
+  String toString() => '$runtimeType(performance: $_performance)';
+}
+
+class _Page extends StatefulComponent {
+  _Page({ Key key, this.route }) : super(key: key);
+
+  final PageRoute route;
+
+  _PageState createState() => new _PageState();
+}
+
+class _PageState extends State<_Page> {
+  final AnimatedValue<Point> _position =
+      new AnimatedValue<Point>(const Point(0.0, 75.0), end: Point.origin, curve: Curves.easeOut);
+
+  final AnimatedValue<double> _opacity =
+      new AnimatedValue<double>(0.0, end: 1.0, curve: Curves.easeOut);
+
+  Widget build(BuildContext context) {
+    return new SlideTransition(
+      performance: config.route.performance,
+      position: _position,
+      child: new FadeTransition(
+        performance: config.route.performance,
+        opacity: _opacity,
+        child: _invokeBuilder()
+      )
+    );
+  }
+
+  Widget _invokeBuilder() {
+    Widget result = config.route.builder(null);
+    assert(() {
+      if (result == null)
+        debugPrint('The builder for route \'${config.route.name}\' returned null. Route builders must never return null.');
+      assert(result != null && 'A route builder returned null. See the previous log message for details.' is String);
+      return true;
+    });
+    return result;
+  }
+}
+
+class PageRoute extends TransitionRoute {
+  PageRoute({
+    this.builder,
+    this.name: '<anonymous>',
+    this.mostValuableKeys
+  }) {
+    assert(builder != null);
+  }
+
+  final RouteBuilder builder;
+  final String name;
+  final Set<Key> mostValuableKeys;
+
+  Duration get transitionDuration => const Duration(milliseconds: 150);
+  Widget createWidget() => new _Page(route: this);
+
+  String get debugLabel => '${super.debugLabel}($name)';
+}

packages/flutter/lib/src/widgets/overlay.dart

@@ -0,0 +1,87 @@
+// 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 'basic.dart';
+import 'framework.dart';
+
+class OverlayEntry {
+  OverlayEntry({
+    this.child,
+    bool opaque: false
+  }) : _opaque = opaque;
+
+  final Widget child;
+
+  bool get opaque => _opaque;
+  bool _opaque;
+  void set opaque(bool value) {
+    _opaque = value;
+    _state?.setState(() {});
+  }
+
+  OverlayState _state;
+
+  /// Remove the entry from the overlay.
+  void remove() {
+    _state?._remove(this);
+    _state = null;
+  }
+}
+
+class Overlay extends StatefulComponent {
+  Overlay({
+    Key key,
+    this.initialEntries
+  }) : super(key: key);
+
+  final List<OverlayEntry> initialEntries;
+
+  OverlayState createState() => new OverlayState();
+}
+
+class OverlayState extends State<Overlay> {
+  final List<OverlayEntry> _entries = new List<OverlayEntry>();
+
+  void initState() {
+    super.initState();
+    for (OverlayEntry entry in config.initialEntries)
+      insert(entry);
+  }
+
+  void insert(OverlayEntry entry, { OverlayEntry above }) {
+    assert(entry._state == null);
+    if (above != null) {
+      print('above._state ${above._state} --- ${above._state == this}');
+      print('_entries.contains ${_entries.contains(above)}');
+    }
+    assert(above == null || (above._state == this && _entries.contains(above)));
+    entry._state = this;
+    setState(() {
+      int index = above == null ? _entries.length : _entries.indexOf(above) + 1;
+      _entries.insert(index, entry);
+    });
+  }
+
+  void _remove(OverlayEntry entry) {
+    setState(() {
+      _entries.remove(entry);
+    });
+  }
+
+  Widget build(BuildContext context) {
+    List<Widget> backwardsChildren = <Widget>[];
+
+    for (int i = _entries.length - 1; i >= 0; --i) {
+      OverlayEntry entry = _entries[i];
+      backwardsChildren.add(new KeyedSubtree(
+        key: new ObjectKey(entry),
+        child: entry.child
+      ));
+      if (entry.opaque)
+        break;
+    }
+
+    return new Stack(backwardsChildren.reversed.toList(growable: false));
+  }
+}