Refactors setting of last score in demo game to use callback

packages/flutter/example/game/lib/game_demo_world.dart

@@ -51,7 +51,9 @@ class GameDemoWorld extends NodeWithSize {
   // Heads up display
   Hud _hud;
 
-  GameDemoWorld(App app, this._navigator, ImageMap images, this._spriteSheet, this._spriteSheetUI) : super(new Size(_gameSizeWidth, _gameSizeHeight)) {
+  Function _gameOverCallback;
+
+  GameDemoWorld(App app, this._navigator, ImageMap images, this._spriteSheet, this._spriteSheetUI, this._gameOverCallback) : super(new Size(_gameSizeWidth, _gameSizeHeight)) {
     // Fetch images
     _imgNebula = images["assets/nebula.png"];
 
@@ -348,7 +350,7 @@ class GameDemoWorld extends NodeWithSize {
 
     // Set game over
     _isGameOver = true;
-    lastScore = _hud.score;
+    _gameOverCallback(_hud.score);
 
     // Remove the ship
     _ship.visible = false;

packages/flutter/example/game/main.dart

@@ -54,6 +54,7 @@ class GameDemoApp extends App {
 
   NavigationState _navigationState;
   GameDemoWorld _game;
+  int _lastScore = 0;
 
   void initState() {
     _navigationState = new NavigationState([
@@ -93,8 +94,7 @@ class GameDemoApp extends App {
   Widget _buildMainScene(navigator, route) {
     return new Stack([
       new SpriteWidget(new MainScreenBackground()),
-      new Center(
-        child: new Flex([
+      new Flex([
         new TextureButton(
           onPressed: () {
             _game = new GameDemoWorld(
@@ -102,7 +102,10 @@ class GameDemoApp extends App {
               navigator,
               _loader,
               _spriteSheet,
-                _spriteSheetUI
+              _spriteSheetUI,
+              (lastScore) {
+                setState(() {_lastScore = lastScore;});
+              }
             );
             navigator.pushNamed('/game');
           },
@@ -112,19 +115,16 @@ class GameDemoApp extends App {
           height: 128.0
         ),
         new Text(
-            "Last Score: $lastScore",
+          "Last Score: $_lastScore",
           style: new TextStyle(fontSize:20.0)
         )
       ],
       direction: FlexDirection.vertical,
       justifyContent: FlexJustifyContent.center)
-      )
     ]);
   }
 }
 
-int lastScore = 0;
-
 class TextureButton extends ButtonBase {
   TextureButton({
     Key key,