Why does opening the keyboard on bottom sheet trigger a rebuild of the parent ListsScreen Stateless widget?

[Hassan Hammad]

I have a simple Lists Screen where i fetch data from an API, and show it in a "UserListsListViewWidget" and i have a couple of other widgets in the screen. 

I have an Add a List button, which opens up a modal bottom sheet sheet with a textfield and a couple of buttons. 

My question is, when i open the bottom sheet and tap the textfield to open the keyboard, the Lists Screen gets rebuilt entirely. And due to that so do all of its children widgets.

Why does this happen? I have added constant constructors almost everywhere, and the bottom sheet is not a stateful widget either which may trigger a rebuild (even if it was, technically it should only rebuild itself, not its parent), so its a strange behaviour that i cannot understand at all. Can you please help me out with this? 

class ListsScreen extends StatelessWidget {
  const ListsScreen();
  static const routeName = '/lists-screen';

  @override
  Widget build(BuildContext context) {
    final user = Provider.of<AuthProvider>(context, listen: false).getUser;
    print('stateless rebuilding');
    return Scaffold(
      appBar: AppBar(
        centerTitle: false,
        title: Text(
          '${user['name']}\'s Lists',
          style: TextStyle(
            color: Theme.of(context).primaryColorLight,
          ),
        ),
        actions: <Widget>[
          const SignOutButton(),
        ],
      ),
      body: Center(
        child: Padding(
          padding: const EdgeInsets.all(20.0),
          child: Column(
            children: <Widget>[
              SizeConfig.smallDevice
                  ? const SizedBox(
                      height: 30,
                    )
                  : const SizedBox(
                      height: 40,
                    ),
              SizeConfig.smallDevice
                  ? Text(
                      'Welcome to TODOS',
                      textAlign: TextAlign.center,
                      style: TextStyle(
                        fontSize: 20,
                        color: Colors.grey[700],
                      ),
                    )
                  : Text(
                      'Welcome to TODOS',
                      textAlign: TextAlign.center,
                      style: TextStyle(
                        fontSize: 25,
                        color: Colors.grey[700],
                      ),
                    ),
              SizeConfig.smallDevice
                  ? const SizedBox(
                      height: 30,
                    )
                  : const SizedBox(
                      height: 40,
                    ),
              const AddNewListButton(),
              SizeConfig.smallDevice
                  ? const SizedBox(
                      height: 30,
                    )
                  : const SizedBox(
                      height: 40,
                    ),
              const UserListsListViewWidget(),
            ],
          ),
        ),
      ),
    );
  }
}

class SignOutButton extends StatelessWidget {
  const SignOutButton();

  Future<void> _submitRequest(BuildContext context) async {
    _showLoadingAlert(context);

    try {
      await Provider.of<AuthProvider>(context, listen: false)
          .submitLogOutRequest();
      Navigator.of(context).pop();
      Navigator.of(context).pushReplacementNamed(LoginScreen.routeName);
    } on HttpExceptions catch (error) {
      Navigator.of(context).pop();
      _showErrorDialogue(error.getErrorList, context);
    }
  }

  void _showErrorDialogue(List<dynamic> errorMessages, BuildContext context) {
    showDialog(
      context: context,
      builder: (ctx) => Dialog(
        shape: RoundedRectangleBorder(
          borderRadius: BorderRadius.circular(20.0),
        ),
        child: ErrorListWidget(errorMessages: errorMessages),
      ),
    );
  }

  void _showLoadingAlert(BuildContext context) {
    showDialog(
      context: context,
      builder: (ctx) => const LoadingWidget(),
    );
  }

  @override
  Widget build(BuildContext context) {
    return FlatButton(
      onPressed: () => _submitRequest(context),
      child: Row(
        children: <Widget>[
          Text(
            'Sign Out',
            style: TextStyle(
              color: Theme.of(context).primaryColorLight,
            ),
          ),
          Icon(
            Icons.exit_to_app,
            color: Theme.of(context).primaryColorLight,
          ),
        ],
      ),
    );
  }
}

class AddNewListButton extends StatelessWidget {
  const AddNewListButton();

  void _modalBottomSheetMenu(BuildContext context) {
    showModalBottomSheet(
      context: context,
      backgroundColor: Colors.transparent,
      isScrollControlled: true,
      builder: (builder) {
        return const ListScreenBottomSheetWidget();
      },
    );
  }

  @override
  Widget build(BuildContext context) {
    return RaisedButton(
      shape: RoundedRectangleBorder(
        borderRadius: BorderRadius.circular(5),
      ),
      elevation: 10,
      color: Theme.of(context).primaryColor,
      onPressed: () => _modalBottomSheetMenu(context),
      child: Text(
        '+ Add List',
        style: TextStyle(
          color: Colors.white,
          fontSize: SizeConfig.smallDevice ? 10 : 15,
        ),
      ),
    );
  }
}