flutter: type '(List<Animal>) => Null' is not a subtype of type '((List<A-CodePudding

I'm trying to use the multiselect package on pub.dev and i realized that the chip choice is what i'm gonna need, i decided to test out the example given on the latest version, and i basically copy pasted the code (with understanding it ofc) but it keeps giving me this error!

then I even opted to make the "values" of the onTap (List) but it gives error afterwards.

here's my code:

class _MyHomePageState extends State<MyHomePage> {
  static List<Animal> _animals = [
    Animal(id: 1, name: "Lion"),
    Animal(id: 2, name: "Flamingo"),
    Animal(id: 3, name: "Hippo"),
    ................
  ];

  final _items = _animals
      .map((animal) => MultiSelectItem<Animal>(animal, animal.name))
      .toList();
  List<Animal> _selectedAnimals = [];

  final _multiSelectKey = GlobalKey<FormFieldState>();



  @override
  Widget build(BuildContext context) {

    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: SingleChildScrollView(
        child: Container(
          child: Column(children: <Widget>[
            MultiSelectChipField<Animal>(
              items: _items,
              initialValue: [_animals[4], _animals[7], _animals[9]],
              title: Text("Animals"),
              headerColor: Colors.blue.withOpacity(0.5),
              decoration: BoxDecoration(
                border: Border.all(color: Colors.blue.shade700, width: 1.8),
              ),
              selectedChipColor: Colors.blue.withOpacity(0.5),
              selectedTextStyle: TextStyle(color: Colors.blue[800]),
//this is where my error is:
              onTap: (values) {
                _selectedAnimals = values;
              },
            ),
            SizedBox(height: 40),

          ]),
        ),
      ),
    
    );
  }
}

CodePudding user response：

You're right, the provided example does not work.

You have to specify correct type Animal? at several place.

Please see the following code:

import 'package:flutter/material.dart';
import 'package:multi_select_flutter/multi_select_flutter.dart';

class Animal {
  final int id;
  final String name;
  const Animal({required this.id, required this.name});
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  static final List<Animal> _animals = [
    const Animal(id: 1, name: 'Lion'),
    const Animal(id: 2, name: 'Flamingo'),
    const Animal(id: 3, name: 'Hippo'),
    const Animal(id: 4, name: 'Horse'),
  ];

  final _items = _animals
      .map((animal) => MultiSelectItem<Animal?>(animal, animal.name)) // Either write Animal? here
      .toList();
  List<Animal?> _selectedAnimals = [];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: MultiSelectChipField<Animal?>( // or write Animal? here
        items: _items,
        initialValue: [
          _animals[0],
          _animals[1],
        ],
        title: const Text('Animals'),
        headerColor: Colors.blue.withOpacity(0.5),
        decoration: BoxDecoration(
          border: Border.all(color: Colors.blue.shade700, width: 1.8),
        ),
        selectedChipColor: Colors.blue.withOpacity(0.5),
        selectedTextStyle: TextStyle(color: Colors.blue[800]),
//this is where my error is:
        onTap: (List<Animal?> values) { // You apparently have to specify the type here as well
          setState(() {
            _selectedAnimals = values;
          });
        },
      ),
    );
  }
}

PS: It helps if you provide a full working example as code snippet. E.g. I had to add the Animal class myself and complete the stateful widget boilerplate to get it running.