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([
@@ -93,38 +94,37 @@ class GameDemoApp extends App {
   Widget _buildMainScene(navigator, route) {
     return new Stack([
       new SpriteWidget(new MainScreenBackground()),
-      new Center(
-        child: new Flex([
-          new TextureButton(
-            onPressed: () {
-              _game = new GameDemoWorld(
-                _app,
-                navigator,
-                _loader,
-                _spriteSheet,
-                _spriteSheetUI
-              );
-              navigator.pushNamed('/game');
-            },
-            texture: _spriteSheetUI["btn_play_up.png"],
-            textureDown: _spriteSheetUI["btn_play_down.png"],
-            width: 128.0,
-            height: 128.0
-          ),
-          new Text(
-            "Last Score: $lastScore",
-            style: new TextStyle(fontSize:20.0)
-          )
-        ],
-        direction: FlexDirection.vertical,
-        justifyContent: FlexJustifyContent.center)
-      )
+      new Flex([
+        new TextureButton(
+          onPressed: () {
+            _game = new GameDemoWorld(
+              _app,
+              navigator,
+              _loader,
+              _spriteSheet,
+              _spriteSheetUI,
+              (lastScore) {
+                setState(() {_lastScore = lastScore;});
+              }
+            );
+            navigator.pushNamed('/game');
+          },
+          texture: _spriteSheetUI["btn_play_up.png"],
+          textureDown: _spriteSheetUI["btn_play_down.png"],
+          width: 128.0,
+          height: 128.0
+        ),
+        new Text(
+          "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,