Use the navigator to stack dialogs.

This removes the need to manually include the dialog builder in the main window's build() function.
It also removes the need to track if a dialog is visible.

Other changes:
- I made dialog.dart a bit more readable.
- I renamed transitionFinished to fullyOpaque since that's what actually matters.
- I made Routes track if they're opaque. Eventually this should probably be more configurable when creating the route.

Directions for Future Research:
- Use this for focus management somehow.
- The popup menu should use something like this.
- We should factor the following out into a showDialog() function that returns a future for the dialog's exit result:
    navigator.push(new DialogRoute(builder: (navigator, route) { ... }));
- Maybe navigator.pop() should take a value to return to that Future.

packages/flutter/example/address_book/lib/main.dart

@@ -68,10 +68,30 @@ class AddressBookApp extends App {
       child: new Icon(type: 'image/photo_camera', size: 24),
       backgroundColor: Theme.of(this).accentColor,
       onPressed: () {
-        showDialog = true;
-        navigator.pushState(this, (_) {
-          showDialog = false;
-        });
+        navigator.push(new DialogRoute(builder: (navigator, route) {
+          return new Dialog(
+            title: new Text("Describe your picture"),
+            content: new ScrollableBlock([
+              new Field(inputKey: fillKey, icon: "editor/format_color_fill", placeholder: "Color"),
+              new Field(inputKey: emoticonKey, icon: "editor/insert_emoticon", placeholder: "Emotion"),
+            ]),
+            onDismiss: navigator.pop,
+            actions: [
+              new FlatButton(
+                child: new Text('DISCARD'),
+                onPressed: () {
+                  navigator.pop();
+                }
+              ),
+              new FlatButton(
+                child: new Text('SAVE'),
+                onPressed: () {
+                  navigator.pop();
+                }
+              ),
+            ]
+          );
+        }));
       }
     );
   }
@@ -104,47 +124,15 @@ class AddressBookApp extends App {
     );
   }
 
-  bool showDialog = false;
-
   Widget buildMain(Navigator navigator) {
-    List<Widget> layers = [
-      new Focus(
+    return new Focus(
       initialFocus: nameKey,
       child: new Scaffold(
         toolbar: buildToolBar(navigator),
         body: buildBody(navigator),
         floatingActionButton: buildFloatingActionButton(navigator)
       )
-      )
-    ];
-    if (showDialog) {
-      layers.add(new Focus(
-        initialFocus: fillKey,
-        child: new Dialog(
-          title: new Text("Describe your picture"),
-          content: new ScrollableBlock([
-            new Field(inputKey: fillKey, icon: "editor/format_color_fill", placeholder: "Color"),
-            new Field(inputKey: emoticonKey, icon: "editor/insert_emoticon", placeholder: "Emotion"),
-          ]),
-          onDismiss: navigator.pop,
-          actions: [
-            new FlatButton(
-              child: new Text('DISCARD'),
-              onPressed: () {
-                navigator.pop();
-              }
-            ),
-            new FlatButton(
-              child: new Text('SAVE'),
-              onPressed: () {
-                navigator.pop();
-              }
-            ),
-          ]
-        )
-      ));
-    }
-    return new Stack(layers);
+    );
   }
 
   NavigationState _navigationState;

packages/flutter/example/stocks/lib/stock_settings.dart

@@ -18,8 +18,6 @@ class StockSettings extends StatefulComponent {
   BackupMode backup;
   SettingsUpdater updater;
 
-  bool _showModeDialog = false;
-
   void syncFields(StockSettings source) {
     navigator = source.navigator;
     optimism = source.optimism;
@@ -47,10 +45,26 @@ class StockSettings extends StatefulComponent {
         _handleOptimismChanged(false);
         break;
       case StockMode.pessimistic:
-        _showModeDialog = true;
-        navigator.pushState(this, (_) {
-          _showModeDialog = false;
-        });
+        navigator.push(new DialogRoute(builder: (navigator, route) {
+          return new Dialog(
+            title: new Text("Change mode?"),
+            content: new Text("Optimistic mode means everything is awesome. Are you sure you can handle that?"),
+            onDismiss: navigator.pop,
+            actions: [
+              new FlatButton(
+                child: new Text('NO THANKS'),
+                onPressed: navigator.pop
+              ),
+              new FlatButton(
+                child: new Text('AGREE'),
+                onPressed: () {
+                  _handleOptimismChanged(true);
+                  navigator.pop();
+                }
+              ),
+            ]
+          );
+        }));
         break;
     }
   }
@@ -104,32 +118,9 @@ class StockSettings extends StatefulComponent {
   }
 
   Widget build() {
-    List<Widget> layers = [
-      new Scaffold(
+    return new Scaffold(
       toolbar: buildToolBar(),
       body: buildSettingsPane()
-      )
-    ];
-    if (_showModeDialog) {
-      layers.add(new Dialog(
-        title: new Text("Change mode?"),
-        content: new Text("Optimistic mode means everything is awesome. Are you sure you can handle that?"),
-        onDismiss: navigator.pop,
-        actions: [
-          new FlatButton(
-            child: new Text('NO THANKS'),
-            onPressed: navigator.pop
-          ),
-          new FlatButton(
-            child: new Text('AGREE'),
-            onPressed: () {
-              _handleOptimismChanged(true);
-              navigator.pop();
-            }
-          ),
-        ]
-      ));
-    }
-    return new Stack(layers);
+    );
   }
 }

packages/flutter/lib/widgets/dialog.dart

@@ -46,14 +46,11 @@ class Dialog extends Component {
   }
 
   Widget build() {
-    Container mask = new Container(
-      decoration: const BoxDecoration(
-        backgroundColor: const Color(0x7F000000)));
 
-    List<Widget> children = new List<Widget>();
+    List<Widget> dialogBody = new List<Widget>();
 
     if (title != null) {
-      children.add(new Padding(
+      dialogBody.add(new Padding(
         padding: new EdgeDims(24.0, 24.0, content == null ? 20.0 : 0.0, 24.0),
         child: new DefaultTextStyle(
           style: Theme.of(this).text.title,
@@ -63,7 +60,7 @@ class Dialog extends Component {
     }
 
     if (content != null) {
-      children.add(new Padding(
+      dialogBody.add(new Padding(
         padding: const EdgeDims(20.0, 24.0, 24.0, 24.0),
         child: new DefaultTextStyle(
           style: Theme.of(this).text.subhead,
@@ -73,11 +70,15 @@ class Dialog extends Component {
     }
 
     if (actions != null)
-      children.add(new Flex(actions, justifyContent: FlexJustifyContent.end));
+      dialogBody.add(new Flex(actions, justifyContent: FlexJustifyContent.end));
 
     return new Stack([
       new Listener(
-        child: mask,
+        child: new Container(
+          decoration: const BoxDecoration(
+            backgroundColor: const Color(0x7F000000)
+          )
+        ),
         onGestureTap: (_) => onDismiss()
       ),
       new Center(
@@ -89,12 +90,13 @@ class Dialog extends Component {
               level: 4,
               color: _color,
               child: new ShrinkWrapWidth(
-                child: new ScrollableBlock(children)
+                child: new ScrollableBlock(dialogBody)
               )
             )
           )
         )
       )
     ]);
+
   }
 }

packages/flutter/lib/widgets/navigator.dart

@@ -9,22 +9,40 @@ import 'package:sky/widgets/animated_component.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:vector_math/vector_math.dart';
 
-typedef Widget Builder(Navigator navigator, RouteBase route);
+typedef Widget RouteBuilder(Navigator navigator, RouteBase route);
 
 abstract class RouteBase {
   Widget build(Navigator navigator, RouteBase route);
+  bool get isOpaque;
   void popState() { }
 }
 
 class Route extends RouteBase {
   Route({ this.name, this.builder });
+
   final String name;
-  final Builder builder;
+  final RouteBuilder builder;
+
   Widget build(Navigator navigator, RouteBase route) => builder(navigator, route);
+  bool get isOpaque => true;
 }
 
-class RouteState extends RouteBase {
+class DialogRoute extends RouteBase {
+  DialogRoute({ this.builder, this.callback });
+
+  final RouteBuilder builder;
+  Function callback;
+
+  Widget build(Navigator navigator, RouteBase route) => builder(navigator, route);
+  bool get isOpaque => false;
 
+  void popState() {
+    if (callback != null)
+      callback(this);
+  }
+}
+
+class RouteState extends RouteBase {
   RouteState({ this.callback, this.route, this.owner });
 
   Function callback;
@@ -32,6 +50,7 @@ class RouteState extends RouteBase {
   StatefulComponent owner;
 
   Widget build(Navigator navigator, RouteBase route) => null;
+  bool get isOpaque => false;
 
   void popState() {
     if (callback != null)
@@ -52,7 +71,7 @@ class Transition extends AnimatedComponent {
     this.onDismissed,
     this.onCompleted,
     this.interactive
-  }) : super(key: key);
+  }): super(key: key);
   Widget content;
   TransitionDirection direction;
   bool interactive;
@@ -145,7 +164,7 @@ class Transition extends AnimatedComponent {
 class HistoryEntry {
   HistoryEntry({ this.route });
   final RouteBase route;
-  bool transitionFinished = false;
+  bool fullyOpaque = false;
   // TODO(jackson): Keep track of the requested transition
 }
 
@@ -182,7 +201,7 @@ class NavigationState {
     if (historyIndex > 0) {
       HistoryEntry entry = history[historyIndex];
       entry.route.popState();
-      entry.transitionFinished = false;
+      entry.fullyOpaque = false;
       historyIndex--;
     }
   }
@@ -231,7 +250,7 @@ class Navigator extends StatefulComponent {
     List<Widget> visibleRoutes = new List<Widget>();
     for (int i = 0; i < state.history.length; i++) {
       // Avoid building routes that are not visible
-      if (i + 1 < state.history.length && state.history[i + 1].transitionFinished)
+      if (i + 1 < state.history.length && state.history[i + 1].fullyOpaque)
         continue;
       HistoryEntry historyEntry = state.history[i];
       Widget content = historyEntry.route.build(this, historyEntry.route);
@@ -253,7 +272,7 @@ class Navigator extends StatefulComponent {
         },
         onCompleted: () {
           setState(() {
-            historyEntry.transitionFinished = true;
+            historyEntry.fullyOpaque = historyEntry.route.isOpaque;
           });
         }
       );