I've been getting the following error on my Flutter Application:

The argument type 'Null' can't be assigned to the parameter type 'Task'.

this is my homepage.dart

// ignore_for_file: prefer_const_literals_to_create_immutables

import 'package:flutter/material.dart';
import 'package:flutter_to_do/database_helper.dart';
import 'package:flutter_to_do/screens/taskpage.dart';
import 'package:flutter_to_do/widgets.dart';

class Homepage extends StatefulWidget {
  @override
  _HomepageState createState() => _HomepageState();
}

class _HomepageState extends State<Homepage> {
  DatabaseHelper _dbHelper = DatabaseHelper();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: Container(
          width: double.infinity,
          padding: const EdgeInsets.symmetric(horizontal: 24.0),
          color: const Color(0xFFF6F6F6),
          child: Stack(
            children: [
              Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: [
                  Container(
                    margin: const EdgeInsets.only(
                      top: 32.0,
                      bottom: 32.0,
                    ),
                    child: const Image(
                      image: AssetImage('assets/images/logo.png'),
                    ),
                  ),
                  Expanded(
                    child: FutureBuilder(
                      initialData: [],
                      future: _dbHelper.getTasks(),
                      builder: (context, AsyncSnapshot snapshot) {
                        return ScrollConfiguration(
                          behavior: NoGlowBehaviour(),
                          child: ListView.builder(
                            itemCount: snapshot.data.length,
                            itemBuilder: (context, index) {
                              return GestureDetector(
                                onTap: () {
                                  Navigator.push(
                                    context,
                                    MaterialPageRoute(
                                      builder: (context) => Taskpage(
                                        task: snapshot.data[index],
                                      ),
                                    ),
                                  ).then(
                                    (value) {
                                      setState(() {});
                                    },
                                  );
                                },
                                child: TaskCardWidget(
                                  title: snapshot.data[index].title,
                                  desc: snapshot.data[index].description,
                                ),
                              );
                            },
                          ),
                        );
                      },
                    ),
                  )
                ],
              ),
              Positioned(
                bottom: 24.0,
                right: 0.0,
                child: GestureDetector(
                  onTap: () {
                    Navigator.push(
                      context,
                      MaterialPageRoute(
                          builder: (context) => Taskpage(
                                task: null,
                              )),
                    ).then((value) {
                      setState(() {});
                    });
                  },
                  child: Container(
                    width: 60.0,
                    height: 60.0,
                    decoration: BoxDecoration(
                      gradient: const LinearGradient(
                          colors: [Color(0xFF7349FE), Color(0xFF643FDB)],
                          begin: Alignment(0.0, -1.0),
                          end: Alignment(0.0, 1.0)),
                      borderRadius: BorderRadius.circular(20.0),
                    ),
                    child: const Image(
                      image: AssetImage(
                        "assets/images/add_icon.png",
                      ),
                    ),
                  ),
                ),
              )
            ],
          ),
        ),
      ),
    );
  }
}

The error happens at:

task: null (line 85)

I am a beginner at flutter and been trying to solve this issue for a while now. What should I do to solve it?

CodePudding user response：

You are triyng to navigate to another screen, passing an argument as null and then you use setState. Basically setState will rebuild everytinh under your build method. Try to review this part of your code.

Navigator.push(
                      context,
                      MaterialPageRoute(
                          builder: (context) => Taskpage(
                                task: null,
                              )),
                    ).then((value) {
                      setState(() {});
                    });

CodePudding user response：

This may be a nullable exception. Try doing this: task: snapshot.data[index]!

Otherwise you should allow the task attribute to be nullable by declaring it with a ? before the variable type instead. For more info on nullables in dart visit Sound null safety