Simple support for routing in Sky

sky/sdk/lib/widgets/navigator.dart

Index: sky/sdk/lib/widgets/navigator.dart
diff --git a/sky/sdk/lib/widgets/navigator.dart b/sky/sdk/lib/widgets/navigator.dart
new file mode 100644
index 0000000000000000000000000000000000000000..8f0d62be423690ebedcdc12781a7aee80de860be
--- /dev/null
+++ b/sky/sdk/lib/widgets/navigator.dart
@@ -0,0 +1,57 @@
+// 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';
+
+typedef UINode Builder(Navigator navigator);

[abarth-chromium, 2015/06/16 02:07:55]

Please add a blank line below this line.

[jackson, 2015/06/16 16:46:37]

Done.

+abstract class RouteBase {
+  RouteBase({this.name});
+  final String name;
+  UINode build(Navigator navigator);
+}
+
+class Route extends RouteBase {
+  Route({String name, this.builder}) : super(name: name);
+  final Builder builder;
+  UINode build(Navigator navigator) => builder(navigator);
+}
+
+class Navigator extends Component {
+  Navigator({Object key, RouteBase initialRoute, this.routes}) 
+    : super(key: key, stateful: true) {
+    assert(initialRoute != null || routes != null && routes.length > 0);
+    currentRoute = initialRoute == null ? this.routes[0] : initialRoute;

[abarth-chromium, 2015/06/16 02:07:54]

There's actually a subtle bug in this class.  The problem is that if the app
rebuilds, this logic will set the currentRoute and syncFields will copy that
current route into the existing Navigator.  That will blow away whatever route
history we have.

Instead, I'd recommend renaming initialRoute to currentRoute and removing the
routes[0] logic.  In build(), below, if currentRoute is null, then we can
default to routes[0].

[jackson, 2015/06/16 16:46:37]

Done.

+  }
+
+  RouteBase currentRoute;
+  List<RouteBase> routes;
+ 
+  void syncFields(Navigator source) {
+    currentRoute = source.currentRoute;
+    routes = source.routes;
+  }
+
+  void pushNamedRoute(String name) {
+    assert(routes != null);
+    for (RouteBase route in routes) {
+      if (route.name == name) {
+        setState(() {
+          currentRoute = route;
+        });
+        return;
+      }
+    }
+    assert(false);  // route not found
+  }
+
+  void pushRoute(RouteBase route) {
+    setState(() {
+      currentRoute = route;
+    });
+  }
+
+  UINode build() {
+    return currentRoute.build(this);

[abarth-chromium, 2015/06/16 02:07:54]

For example,

if (currentRoute == null)
  return routes[0].build(this);
return currentRoute.build(this);

+  }
+}