Flutter - UnimplementedError

Issue

I started getting errors out of the blue with the following codes:

class app extends StatefulWidget {
  @override
  State<app> createState() => _appState();
}

String ad;
String profilFoto;

int selectedIndex;

class _appState extends State<app> {
  @override
  void initState()  {
    super.initState();
    //await FirebaseAuth.instance.signOut();
  PersistentTabController _controller = PersistentTabController(initialIndex: 0);
  Widget build(BuildContext context) {
    return PersistentTabView(
      context,
      controller: _controller,
        screens: _buildScreens(),
        items: _navBarsItems(),
        confineInSafeArea: true,
        backgroundColor: Colors.white, // Default is Colors.white.
        handleAndroidBackButtonPress: true, // Default is true.
        resizeToAvoidBottomInset: true, // This needs to be true if you want to move up the screen when keyboard appears. Default is true.
        stateManagement: true, // Default is true.
        hideNavigationBarWhenKeyboardShows: true, // Recommended to set 'resizeToAvoidBottomInset' as true while using this argument. Default is true.
        decoration: NavBarDecoration(
          borderRadius: BorderRadius.circular(10.0),
          colorBehindNavBar: Colors.white,
        ),
        popAllScreensOnTapOfSelectedTab: true,
        popActionScreens: PopActionScreensType.all,
        itemAnimationProperties: ItemAnimationProperties( // Navigation Bar's items animation properties.
          duration: Duration(milliseconds: 200),
          curve: Curves.ease,
        ),
        screenTransitionAnimation: ScreenTransitionAnimation( // Screen transition animation on change of selected tab.
          animateTabTransition: true,
          curve: Curves.ease,
          duration: Duration(milliseconds: 200),
        ),
        navBarStyle: NavBarStyle.style1, // Choose 
    );
  }
  void _onItemTapped(int index) {
    setState(() {
      selectedIndex  = index;
    });
  }
}
  List<Widget> _buildScreens() {
    return [
      MainScreen(),
      settingsScreen()
    ];
  }
    List<PersistentBottomNavBarItem> _navBarsItems() {
        return [
          PersistentBottomNavBarItem(
            icon: Icon(Icons.home),
            title: ("Görevler"),
            activeColorPrimary: Colors.blueAccent,
            inactiveColorPrimary: Colors.grey,
            textStyle: TextStyle(fontSize: 25),
          ),
          PersistentBottomNavBarItem(
            icon: Icon(Icons.person),
            title: ("Hesap"),
            activeColorPrimary: Colors.blueAccent,
            inactiveColorPrimary: Colors.grey,
            textStyle: TextStyle(fontSize: 25),
          ),
        ];
    }

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    throw UnimplementedError();
  }
}

---

Error:

When I tried the code a few hours ago, it was not giving any errors. Now it started giving this error out of the blue. I didn't make any changes.

It started giving this error out of the blue. Thank you in advance for your valuable answers.

Solution

class app extends StatefulWidget {
  @override
  State<app> createState() => _appState();
}

class _appState extends State<app> {
  String ad;
  String profilFoto;

  int selectedIndex;

  PersistentTabController _controller;

  @override
  void initState()  {
    super.initState();
    _controller = PersistentTabController(initialIndex: 0);
    //await FirebaseAuth.instance.signOut();
  }

  void _onItemTapped(int index) {
    setState(() {
      selectedIndex  = index;
    });
  }

  List<Widget> _buildScreens() {
    return [
      MainScreen(),
      settingsScreen()
    ];
  }

  List<PersistentBottomNavBarItem> _navBarsItems() {
    return [
      PersistentBottomNavBarItem(
        icon: Icon(Icons.home),
        title: ("Görevler"),
        activeColorPrimary: Colors.blueAccent,
        inactiveColorPrimary: Colors.grey,
        textStyle: TextStyle(fontSize: 25),
      ),
      PersistentBottomNavBarItem(
        icon: Icon(Icons.person),
        title: ("Hesap"),
        activeColorPrimary: Colors.blueAccent,
        inactiveColorPrimary: Colors.grey,
        textStyle: TextStyle(fontSize: 25),
      ),
    ];
  }


  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: PersistentTabView(
        context,
        controller: _controller,
        screens: _buildScreens(),
        items: _navBarsItems(),
        confineInSafeArea: true,
        backgroundColor: Colors.white, // Default is Colors.white.
        handleAndroidBackButtonPress: true, // Default is true.
        resizeToAvoidBottomInset: true, // This needs to be true if you want to move up the screen when keyboard appears. Default is true.
        stateManagement: true, // Default is true.
        hideNavigationBarWhenKeyboardShows: true, // Recommended to set 'resizeToAvoidBottomInset' as true while using this argument. Default is true.
        decoration: NavBarDecoration(
          borderRadius: BorderRadius.circular(10.0),
          colorBehindNavBar: Colors.white,
        ),
        popAllScreensOnTapOfSelectedTab: true,
        popActionScreens: PopActionScreensType.all,
        itemAnimationProperties: ItemAnimationProperties( // Navigation Bar's items animation properties.
          duration: Duration(milliseconds: 200),
          curve: Curves.ease,
        ),
        screenTransitionAnimation: ScreenTransitionAnimation( // Screen transition animation on change of selected tab.
          animateTabTransition: true,
          curve: Curves.ease,
          duration: Duration(milliseconds: 200),
        ),
        navBarStyle: NavBarStyle.style1, // Choose
      ),
    );
  }
}

Answered By - DholaHardik