The argument type 'void Function(Map<String, bool>)' can't be assigned to the parameter type 'Map<String, bool>'

Issue

I’m trying to send the filter to the filter screen but getting an error.

The argument type ‘void Function(Map<String, bool>)’ can’t be assigned to the parameter type ‘Map<String, bool>’.

Main screen code

import 'package:flutter/material.dart';
import 'package:meal_app/dummy.dart';
import 'package:meal_app/screens/bottom_navigation.dart';
import 'package:meal_app/screens/catagory_item_screen.dart';
import 'package:meal_app/screens/categorise_screen.dart';
import 'package:meal_app/screens/filters_screen.dart';
import 'package:meal_app/screens/homescreen.dart';
import 'package:meal_app/screens/meal_item_details.dart';
import 'package:meal_app/widgets/meal.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  // This widget is the root of your application.
  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  Map<String, bool> _filter = {
    'gluton': false,
    'lactose': false,
    "vrgan": false,
    "vegetarian": false
  };
  List<Meal> _availablemeal = DUMMY_MEALS;
  void _applyfilter(Map<String, bool> filterData) {
    setState(() {
      _filter = filterData;
      _availablemeal = DUMMY_MEALS.where((meals) {
        if (_filter['gluton']! && !meals.isGlutenFree) {}
        if (_filter['lactose']! && !meals.isLactoseFree) {
          return false;
        }
        if (_filter['vrgan']! && !meals.isVegan) {
          return false;
        }
        if (_filter['vegetarian']! && !meals.isVegetarian) {
          return false;
        }
        return true;
      }).toList();
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Meal App',
      theme: ThemeData(
        primarySwatch: Colors.pink,
        accentColor: Colors.amber,
        canvasColor: Color.fromRGBO(255, 255, 255, 1),
        fontFamily: 'Raleway',
        textTheme: ThemeData.light().textTheme.copyWith(
              bodyText1: TextStyle(
                color: Color.fromRGBO(20, 50, 51, 1),
              ),
              bodyText2: TextStyle(color: Color.fromRGBO(20, 50, 51, 1)),
              subtitle1: TextStyle(
                  fontSize: 20,
                  fontWeight: FontWeight.bold,
                  fontFamily: "RobotoCondensed"),
            ),
      ),
      initialRoute: '/',
      routes: {
        '/': (ctx) => BottomNavigation(),
        CatagoryItemScreen.routes: (ctx) => CatagoryItemScreen(_availablemeal),
        MealDetails.routs: (ctx) => MealDetails(),
        FiltersScreen.routeName: (ctx) => FiltersScreen(_filter, _applyfilter),
      },
    );
  }
}

When i was using final VoidCallBack it was placing no error in main.dart but giving error in onPressed:widget.applyfilter(selectedfilter); then i replaced VoidCallBack with Function(Map) then it start giving error in main.dart code.

Filter screen

import 'package:flutter/material.dart';
import 'package:meal_app/widgets/drawer.dart';

class FiltersScreen extends StatefulWidget {
  final Function(Map) applyfilter;
  final Map<String, bool> currentfilter;
  FiltersScreen(this.applyfilter, this.currentfilter);
  static const routeName = '/filter';

  @override
  State<FiltersScreen> createState() => _FiltersScreenState();
}

class _FiltersScreenState extends State<FiltersScreen> {
  Widget _buildSwitchTile(String title, String subTitle, var currentVal,
      Function(bool) nextQuestion) {
    return SwitchListTile(
      title: Text(title),
      subtitle: Text(subTitle),
      value: currentVal,
      activeColor: Colors.redAccent,
      onChanged: nextQuestion,
    );
  }

  var isGlutenFree = false;
  var isLactoseFree = false;
  var isVegan = false;
  var isVegetarian = false;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Filter Screen"),
        actions: [
          IconButton(
              icon: Icon(Icons.save),
              onPressed: () {
                final selectedfilter = {
                  'gluton': isGlutenFree,
                  'lactose': isLactoseFree,
                  "vrgan": isVegan,
                  "vegetarian": isVegetarian
                };
                widget.applyfilter(selectedfilter);
              })
        ],
      ),
      drawer: MainDrawer(),
      body: Column(children: [
        Container(
          margin: EdgeInsets.all(20),
          child: Text(
            "Adjust your filters here",
            style: TextStyle(fontWeight: FontWeight.w900, fontSize: 26),
          ),
        ),
        Expanded(
            child: ListView(
          children: [
            _buildSwitchTile(
                "Glutan-Free", "only include Glutan-Free meal", isGlutenFree,
                (newValue) {
              setState(() {
                isGlutenFree = newValue;
              });
            }),
            _buildSwitchTile(
                "Lactose-Free", "only include Lactose-Free meal", isLactoseFree,
                (newValue) {
              setState(() {
                isLactoseFree = newValue;
              });
            }),
            _buildSwitchTile(
                "Vegan-Free", "only include Vegan-Free meal", isVegan,
                (newValue) {
              setState(() {
                isVegan = newValue;
              });
            }),
            _buildSwitchTile("Vegetarian-Free",
                "only include Vegetarian-Free meal", isVegetarian, (newValue) {
              setState(() {
                isVegetarian = newValue;
              });
            }),
          ],
        ))
      ]),
    );
  }
}

Solution

You pass the arguments in the wrong order. Switch them:

FiltersScreen.routeName: (ctx) => FiltersScreen(_applyfilter, _filter)

Also define a matching map type in your Filter screen:

final Function(Map<String, bool>) applyfilter;

(Otherwise you would get another error message after fixing the order of your arguments)

Answered By – hnnngwdlch

Answer Checked By – Candace Johnson (FlutterFixes Volunteer)