Non-final field in Stateless Widget

Question

First, I need to say that I'm not sure if stackoverflow is the right place to ask this, but I have no one to ask except the community because we are working in small startup where there are no flutter developers besides two of us.

Me (about one year in development, and about a half of the year studying flutter) and one kinda "senior mobile developer with 10 years of experience" have fierce discussion.

The topic of the discussion is using non-final field in Stateless widget. He's doing it, he's writing such code. And he's saying that it is the best way to solve his problems. I'm saying that it is the bad idea and either he needs stateful widget or his design is bad and he doesn't need non-final field.

So my question is: Is there a situation in which the use of non-final field in stateless widget is justified?

His arguments:

We are using BLoC pattern, and because in StatelessWidget we have BlocBuilder, this StatelessWidget has state.
Stupid Dart linter doesn't know our "BLoC situation"
If we will use stateful widget, readability of the code getting bad.
If we will use stateful widget we are getting extra overhead.

I know that the first two arguments are silly and only 4th argument is worth to discuss.

Possible duplicate of this question also doesn't convince my colleague. Flutter: Mutable fields in stateless widgets

Please have a look at his code:

class GameDiscussThePicture extends StatelessWidget {

  GameDiscussThePicture();

  CarouselSlider _slider;

  @override
  Widget build(BuildContext context) {
    return BlocBuilder(
      bloc: BlocProvider.of(context),
      condition: (previousState, state) {
        return previousState != GameClosed();
      },
      builder: (context, state) {
        if (state is GameDiscussTopicChanged) {
          _showPictureWith(context, state.themeIndex);
        } else if (state is GameClosed) {
          Navigator.of(context).pop();
          return Container();
        }
      final _chatBloc = BlocProvider.of(context);
      return Scaffold(
        appBar: AppBar(
          backgroundColor: Color.fromARGB(255, 255, 255, 255),
          leading: BackButton(
            color: Color.fromARGB(255, 12, 12, 13),
            onPressed: () => BlocProvider.of(context).add(GameCancel()),
          ),
        ),
        //SafeArea
        body: DecoratedBox(
          decoration: BoxDecoration(color: Color.fromARGB(255, 240, 240, 240)),
          child: Row(
            mainAxisSize: MainAxisSize.max,
            mainAxisAlignment: MainAxisAlignment.start,
            children: [
              Expanded(
                child: Column(
                  mainAxisSize: MainAxisSize.max,
                  mainAxisAlignment: MainAxisAlignment.spaceBetween,
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: [
                    SizedBox(height: 15),
                    _carouselSlider(context),
                    Container(
                      height: 88,
                      child: DecoratedBox(
                        decoration: BoxDecoration(color: Color.fromARGB(255, 255, 255, 255)),
                        child: Row(
                          mainAxisSize: MainAxisSize.max,
                          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                          children: [
                            if (_chatBloc.partnerAvatar() != null) Image.network(_chatBloc.partnerAvatar(), fit: BoxFit.cover, width: 75.0),
                            if (_chatBloc.partnerAvatar() == null) Text('RU', style: TextStyle(fontSize: 22)),
                          Padding(
                            padding: EdgeInsets.fromLTRB(20, 0, 20, 0),
                            child: Column(
                              mainAxisAlignment: MainAxisAlignment.center,
                              crossAxisAlignment: CrossAxisAlignment.start,
                              children: [
                                Text(_chatBloc.partnerName(), style: TextStyle(fontSize: 20, fontWeight: FontWeight.normal),),
                                ChatStopwatch(),
                                // Text('До конца 06:33', style: TextStyle(fontSize: 14, fontWeight: FontWeight.normal),),
                              ],
                            )
                          ),
                          // FlatButton(
                          //   child: Image.asset('assets/images/mic_off.png', width: 30, height: 30,),
                          //   onPressed: () => print('mic off pressed'),
                          // ),
                          FlatButton(
                            child: Image.asset('assets/images/hang_off.png', width: 60, height: 60,),
                            onPressed: () => ChatHelper.confirmEndingDialog(context)
                          ),
                        ]),
                    ))
                  ],
                ),
              ),
            ],
          ),
        ),
      );
    });
  }

  @widget
  Widget _carouselSlider(BuildContext context) {    
    final chatBloc = BlocProvider.of(context);
    _slider = CarouselSlider(
      height: 600.0,
      viewportFraction: 0.9,
      reverse: false,
      enableInfiniteScroll: false,
      initialPage: chatBloc.gameDiscussCurrentIdx,
      onPageChanged: (index) {
        final chatBloc = BlocProvider.of(context);
        if (chatBloc.gameDiscussCurrentIdx < index) {
          chatBloc.add(GameDiscussTopicChange(themeIndex: index));
        } else {
          _slider.animateToPage(chatBloc.gameDiscussCurrentIdx, duration: Duration(milliseconds: 300), curve: Curves.easeInOut);
        }
      },
      items: chatBloc.gameDiscussPictures.map((item) {
        return Builder(
          builder: (BuildContext context) {
            return Container(
              width: MediaQuery.of(context).size.width,
              margin: EdgeInsets.symmetric(horizontal: 5.0),
              child: Column(
                mainAxisSize: MainAxisSize.max,
                mainAxisAlignment: MainAxisAlignment.start,
                crossAxisAlignment: CrossAxisAlignment.start,
                children: [
                  Text(item.titleEn, style: Styles.h3),
                  SizedBox(height: 15.0,),
                  ClipRRect(
                    borderRadius: BorderRadius.all(Radius.circular(15.0)),
                    child: Image.network(item.getImageUrl(), fit: BoxFit.cover, width: MediaQuery.of(context).size.width),
                  )
                ]
              ),
            );
          },
        );
      }).toList(),
    );
    return _slider;
  }

  _onPictureChanged(BuildContext context, int index) {
    final chatBloc = BlocProvider.of(context);
    if (chatBloc.gameDiscussCurrentIdx < index) {
      chatBloc.add(GameDiscussTopicChange(themeIndex: index));
    } else {
      _slider.animateToPage(chatBloc.gameDiscussCurrentIdx, duration: Duration(milliseconds: 300), curve: Curves.easeInOut);
    }
  }

  _showPictureWith(BuildContext context, int index) {
      final chatBloc = BlocProvider.of(context);
      chatBloc.gameDiscussCurrentIdx = index;
      _slider.animateToPage(chatBloc.gameDiscussCurrentIdx, duration: Duration(milliseconds: 300), curve: Curves.easeInOut);
  }
}

Non-final field in Stateless Widget

Answers (1)

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