可空表达式不能用作条件。 在将其用作条件之前，请尝试检查该值是否不是“空”。 flutter /飞镖

Question

I've got a map which contains (4 keys and 4 values) as shown in the code below:

class _MyAppState extends State<MyApp> {
   
  Map<String, bool> _filters  = {
    'gluten': false,
    'lactose': false,
    'vegan': false,
    'vegetarian': false
  };

In order to filter the map to meet certain conditions, I've created a _setFilters Method as shwon below:

 List<Meal> _availabaleMeals =  DUMMY_MEALS;

   void _setFilters(Map<String, bool> filterData){
             setState(() {
               _filters = filterData;
               _availabaleMeals = DUMMY_MEALS.where((meal){
                   if (_filters['gluten']&& !meal.isGlutenFree) {
                     return false;
                   }
                    if (_filters['lactode']e && !meal.isLactoseFree) {
                     return false;
                   }
                    if (_filters['vegan'] && !meal.isVegan) {
                     return false;
                   }
                    if (_filters['vegetarian'] && !meal.isVegetarian) {
                     return false;
                   }
               }).toList();
             });
   }

The problem is dart doesn't accept the if conditions exactly here:

if (_filters['gluten']&& !meal.isGlutenFree) {
                     return false;
                   }
                    if (_filters['lactode']e && !meal.isLactoseFree) {
                     return false;
                   }
                    if (_filters['vegan'] && !meal.isVegan) {
                     return false;
                   }
                    if (_filters['vegetarian'] && !meal.isVegetarian) {
                     return false;
                   }

I'd really appreciate your help guys

Answer 1

You've not showed your "Meal" class here, but if the values are nullable, meaning you've declared properties in it with a "?" or not made them required, you're going to have to make sure they are actually not null.

For example:

if (meal.isLactoseFree != nulL && _filters['lactode'] && !meal.isLactoseFree)

Another very real possibility is that the trailing "e" you have in your second if statement behind "_filters['lactode']" is causing the issue. Lactose is also misspelled in that instance, by the way. Consider using constants if you are going to be referring to keys in multiple places.