I got this error on terminal

lib/pages/pomodoro.dart:31:21: Error: This expression has type 'void' and can't be used. ? null ^

This is my code:

import 'package:braintrinig/components/cronometro.dart';
import 'package:braintrinig/components/entrada_tempo.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter_mobx/flutter_mobx.dart';
import 'package:provider/provider.dart';
import '../pages/pomodoro.store.dart';
import 'package:braintrinig/pages/pomodoro.store.dart';
class Pomodoro extends StatelessWidget {
  const Pomodoro({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final store = Provider.of<PomodoroStore>(context);

    return Scaffold(
      body: Column(
        crossAxisAlignment: CrossAxisAlignment.stretch,
        children: [
          Expanded(child: Cronometro(),
          ),
          Padding(padding: EdgeInsets.symmetric(vertical: 40),
          child: Observer(
            builder: (_) => Row(
            mainAxisAlignment: MainAxisAlignment.spaceAround,
            children: [
              EntradaTempo(
                titulo: 'Work',
                valor: store.tempoWork,
                inc: store.start && store.isWorking()
                    ? null
                : store.incrementarTempoWork(),
                dec: store.reduceTempoRest,
              ),
              EntradaTempo(
                titulo: 'Relax',
                valor: store.tempoRest,
                inc: store.incrementarTempoRest,
                dec: store.reduceTempoRest,
              ),
            ],
          ),
          )
          ),
        ],
      ),
    );
  }
}

The error is here:

How to solve this issue?

Thank you in advance

CodePudding user response：

This is probably due to the fact that either store.start or store.incrementarTempoWork() is not returnning a value and this is void.

Also check that inc accepts null.

inc: store.start && store.isWorking()
   ? null
   : store.incrementarTempoWork(),  // <<<< probably this one is void

CodePudding user response：

In dart while checking conditions the value used to compare must not be null after upgrade to Null Safety. so you have to confirm it with ! symbol.

! symbol tells to compiler that particular field have data...

may be below one work.

inc: store!.start! && store!.isWorking()
   ? null
   : store!.incrementarTempoWork(),