make appbar title change dynamically

lib/pages/main_page.dart

@@ -14,6 +14,13 @@ class MyHomePage extends StatefulWidget {
 
 class MyHomePageState extends State<MyHomePage> {
   int _selectedIndex = 2;
+  final List<String> _titles = [
+    'Stimmung',
+    'Schlaf',
+    'Timer',
+    'Rückfall',
+    'Einstellungen'
+  ];
   static const List<Widget> _widgetOptions = <Widget>[
     MoodPage(),
     SleepPage(),
@@ -29,7 +36,7 @@ class MyHomePageState extends State<MyHomePage> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      appBar: AppBar(title: const Text('ZI Rauchentwöhnung')),
+      appBar: AppBar(title: Text(_titles[_selectedIndex])),
       body: _widgetOptions.elementAt(_selectedIndex),
       bottomNavigationBar: NavigationBar(
         onDestinationSelected: _onItemTapped,