Refactor Navigator to put state in separate class, initial back button plumbing

R=abarth@chromium.org, abarth

Review URL: https://codereview.chromium.org/1195493002.

examples/stocks2/lib/stock_app.dart

@@ -14,19 +14,24 @@ class StocksApp extends App {
 
   StocksApp({ RenderView renderViewOverride }) : super(renderViewOverride: renderViewOverride);
 
+  NavigationState _navState = new NavigationState([
+    new Route(name: '/', builder: (navigator) => new StockHome(navigator)),
+    new Route(name: '/settings', builder: (navigator) => new StockSettings(navigator)),
+  ]);
+
+  void onBack() {
+    if (_navState.hasPrevious()) {
+      setState(() {
+        _navState.pop();
+      });
+      return;
+    }
+    print ("Should exit app here");
+    // TODO(jackson): Need a way to invoke default back behavior here
+  }
+
   Widget build() {
-    return new Navigator(
-      routes: [
-        new Route(
-          name: '/', 
-          builder: (navigator) => new StockHome(navigator)
-        ),
-        new Route(
-          name: '/settings', 
-          builder: (navigator) => new StockSettings(navigator)
-        ),
-      ]
-    );
+    return new Navigator(_navState);
   }
 }
 

examples/widgets/navigation.dart

@@ -65,8 +65,10 @@ List<Route> routes = [
 ];
 
 class NavigationExampleApp extends App {
+  NavigationState _navState = new NavigationState(routes);
+
   Widget build() {
-    return new Flex([new Navigator(routes: routes)]);
+    return new Flex([new Navigator(_navState)]);
   }
 }
 

sdk/lib/app/view.dart

@@ -50,6 +50,8 @@ class AppView {
 
   Function onFrame;
 
+  List<sky.EventListener> eventListeners = new List<sky.EventListener>();
+
   RenderBox get root => _renderView.child;
   void set root(RenderBox value) {
     _renderView.child = value;
@@ -68,6 +70,10 @@ class AppView {
       HitTestResult result = new HitTestResult();
       _renderView.hitTest(result, position: new Point(event.x, event.y));
       dispatchEvent(event, result);
+    } else {
+      for (sky.EventListener listener in eventListeners) {
+        listener(event);
+      }
     }
   }
 

sdk/lib/widgets/navigator.dart

@@ -18,28 +18,23 @@ class Route extends RouteBase {
   Widget build(Navigator navigator) => builder(navigator);
 }
 
-class Navigator extends Component {
-  Navigator({ Object key, RouteBase defaultRoute, List<RouteBase> routes })
-    : super(key: key, stateful: true) {
-    if (routes != null) {
-      if (defaultRoute == null)
-        defaultRoute = routes[0];
-      for (Route route in routes) {
-        if (route.name != null)
-          namedRoutes[route.name] = route;
-      }
+class NavigationState {
+
+  NavigationState(List<Route> routes) {
+    for (Route route in routes) {
+      if (route.name != null)
+        namedRoutes[route.name] = route;
     }
-    assert(defaultRoute != null);
-    _history.add(defaultRoute);
+    history.add(routes[0]);
   }
 
-  List<RouteBase> _history = new List<RouteBase>();
-  int _historyIndex = 0;
+  List<RouteBase> history = new List<RouteBase>();
+  int historyIndex = 0;
   Map<String, RouteBase> namedRoutes = new Map<String, RouteBase>();
 
-  void syncFields(Navigator source) {
-    namedRoutes = source.namedRoutes;
-  }
+  RouteBase get currentRoute => history[historyIndex];
+  bool hasPrevious() => historyIndex > 0;
+  bool hasNext() => history.length > historyIndex + 1;
 
   void pushNamed(String name) {
     Route route = namedRoutes[name];
@@ -48,38 +43,67 @@ class Navigator extends Component {
   }
 
   void push(RouteBase route) {
+    // Discard future history
+    history.removeRange(historyIndex + 1, history.length);
+    historyIndex = history.length;
+    history.add(route);
+  }
+
+  void pop() {
+    if (historyIndex > 0) {
+      history.removeLast();
+      historyIndex--;
+    }
+  }
+
+  void back() {
+    if (historyIndex > 0)
+      historyIndex--;
+  }
+
+  void forward() {
+    historyIndex++;
+    assert(historyIndex < history.length);
+  }
+}
+
+class Navigator extends Component {
+
+  Navigator(this.state, { String key }) : super(key: key);
+
+  NavigationState state;
+
+  void pushNamed(String name) {
     setState(() {
-      // Discard future history
-      _history.removeRange(_historyIndex + 1, _history.length);
-      _historyIndex = _history.length;
-      _history.add(route);
+      state.pushNamed(name);
+    });
+  }
+
+  void push(RouteBase route) {
+    setState(() {
+      state.push(route);
     });
   }
 
   void pop() {
     setState(() {
-      if (_historyIndex > 0) {
-        _history.removeLast();
-        _historyIndex--;
-      }
+      state.pop();
     });
   }
 
   void back() {
     setState(() {
-      if (_historyIndex > 0)
-        _historyIndex--;
+      state.back();
     });
   }
 
   void forward() {
     setState(() {
-      _historyIndex++;
-      assert(_historyIndex < _history.length);
+      state.forward();
     });
   }
 
   Widget build() {
-    return _history[_historyIndex].build(this);
+    return state.currentRoute.build(this);
   }
 }

sdk/lib/widgets/widget.dart

@@ -799,10 +799,17 @@ abstract class App extends AbstractWidgetRoot {
     if (root.parent == null) {
       // we haven't attached it yet
       WidgetAppView._appView.root = root;
+      WidgetAppView._appView.eventListeners.add((event) {
+        if (event.type == "back")
+          onBack();
+      });
     }
     assert(root.parent is RenderView);
   }
 
+  // Override this to handle back button behavior in your app
+  void onBack() { }
+
 }
 
 typedef Widget Builder();