Added the Favorites button.

namer_app/lib/main.dart

@@ -26,13 +26,24 @@ class MyApp extends StatelessWidget {
 }
 
 class MyAppState extends ChangeNotifier {
-  var current = WordPair.random();// ...
+  var current = WordPair.random();
 
-  // ↓ Add this.
   void getNext() {
     current = WordPair.random();
     notifyListeners();
   }
+
+  var favorites = <WordPair>[];
+
+  void toggleFavorite() {
+    if (favorites.contains(current)) {
+      favorites.remove(current);
+    } else {
+      favorites.add(current);
+    }
+    notifyListeners();
+    print("Favorites are: ${favorites.toString()}");
+  }
 }
 
 class MyHomePage extends StatelessWidget {
@@ -41,6 +52,13 @@ class MyHomePage extends StatelessWidget {
     var appState = context.watch<MyAppState>();
     var pair = appState.current;
 
+    IconData icon;
+    if (appState.favorites.contains(pair)) {
+      icon = Icons.favorite;
+    } else {
+      icon = Icons.favorite_border;
+    }
+
     return Scaffold(
       body: Center(
         child: Column(
@@ -48,11 +66,26 @@ class MyHomePage extends StatelessWidget {
           children: [
             BigCard(pair: pair),
             SizedBox(height: 10.0), // Just a spacer.
-            ElevatedButton(
-              onPressed: () {
-                appState.getNext();
-              },
-              child: Text('Next'),
+            Row(
+              mainAxisSize: MainAxisSize.min,
+              children: [
+                ElevatedButton.icon(
+                  onPressed: () {
+                    appState.toggleFavorite();
+                  },
+                  icon: Icon(icon),
+                  label: Text('Favorite'),
+                ),
+
+                SizedBox(width: 10.0),
+
+                ElevatedButton(
+                  onPressed: () {
+                    appState.getNext();
+                  },
+                  child: Text('Next'),
+                ),
+              ],
             ),
           ],
         ),