boolean expression must not be empty error in Flutter

Question

I'm trying to check if the user likes the current post and set an icon. I'm trying to do a simple check but it throws an error.

The method I created

List<String> fav = List<String>();

checkFav(String id) {
    bool isFav = fav.contains(id);

    if(isFav)
      return true;
    else
      return null;
  }

And where I use the method



IconButton(
           icon: Icon(favorite.checkFav(widget.blogModel.id)
               ? Icons.favorite
               : Icons.favorite_border,
                 color: Colors.redAccent),

                    onPressed: () {
                      setState(
                        () {
                          favorite.checkFav(widget.blogModel.id)
                              ? favorite.deleteItemToFav(widget.blogModel.id)
                              : favorite.addItemToFav(widget.blogModel.id);
                        },
                      );
                      //favorite.checkItemInFav(widget.blogModel.id, context);
                    },
                  ),

julemand101 · Accepted Answer · 2021-06-26 12:57:15Z

2

Your checkFav should specify it returns bool. Also, you are returning null in case of false which is properly not what you have intended.

So you can rewrite your method to the following which will properly work:

bool checkFav(String id) => fav.contains(id);

answered Jun 26, 2021 at 12:57

julemand101

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2 Comments

Semih Yilmaz Over a year ago

Yes the error is gone but the icon still does not change

julemand101 Over a year ago

@SemihYılmaz Well, that is an entire different issue which is not even part of your question. Please make another question for that problem,

Yauheni Prakapenka · Accepted Answer · 2021-06-26 16:20:44Z

0

Good day. Try this code:

class MyHomePage extends StatelessWidget {
  final _favorites = <String>['1', '2', '3'];

  @override
  Widget build(BuildContext context) {
    final buttonIsActive = checkFavorites('1', _favorites);
    return Scaffold(
      body: Center(
        body: Center(child: buildFavoriteButton(isActive: buttonIsActive)),
       ),
    );
  }
}

bool checkFavorites(String id, List<String> favorites) {
  return favorites.contains(id);
}

Widget buildFavoriteButton({bool isActive = false}) {
  return IconButton(
    icon: Icon(
      Icons.ac_unit,
      color: isActive ? Colors.red : Colors.grey,
    ),
    onPressed: () {},
  );
}

edited Jun 26, 2021 at 16:20

answered Jun 26, 2021 at 14:45

Yauheni Prakapenka

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