I got this error from terminal, tried to make “PomodoroStatus” a variable changed to capitalize letter to “p”, but no luck, how to solve it?

(red warning) lib/screens/home_screen.dart:71:40: Error: The argument type 'String?' can't be assigned to the parameter type 'String' because 'String?' is nullable and 'String' isn't. statusDescription[PomodoroStatus],

this is my code:

import 'dart:async';
import 'package:startup_pomodoro/utils/constants.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:percent_indicator/circular_percent_indicator.dart';
import '../utils/constants.dart';
import '../widget/progress_icons.dart';
import '../widget/custom_button.dart';
import '../model/pomodoro_status.dart';

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

  @override
  State<Home> createState() => _HomeState();
}
const _btnTextStart = 'Start Pomodoro';
const _btnTextResumePomodoro = 'Resume Pomodoro';
const _btnTextResumeBreak = 'Resume Break';
const _btnTextStartShortBreak = 'Take Short Break';
const _btnTextStartLongBreak = 'Take Long Break';
const _btnTextStartNewSet = 'Start New Set';
const _btnTextPause = 'Pause';
const _btnTextReset = 'Reset';

class _HomeState extends State<Home> {

  int remainingTime = pomodoroTotalTime;
  String mainBtnText = _btnTextStart;
  PomodoroStatus pomodoroStatus = PomodoroStatus.pausedPomodoro;
  late Timer _timer;
  int pomodoroNum = 0;
  int setNum = 0;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Color(0xFFD95550),
      body: SafeArea(
        child: Center(
          child: Column(children: [
            SizedBox(height: 10,),
            Text(“Pomodoro number:$pomodoroNum”,
              style: TextStyle(fontSize: 32, color: Colors.white),
            ),
            SizedBox(height: 10,),
            Text(“Set: $setNum”,
              style: TextStyle(fontSize: 32, color: Colors.white),
            ),
            Expanded(
                child: Column(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: [
                    CircularPercentIndicator(
                      backgroundColor: Color(0xFFF5EEEE),
                        radius: 150.0,
                      lineWidth: 15.0,
                      percent: 0.3,
                        circularStrokeCap: CircularStrokeCap.round,
                        center: Text(_secondsToFormatedString(remainingTime),
                        style: TextStyle(fontSize: 40, color: Colors.white),
                        ),
                      progressColor: statusColor[pomodoroStatus],
                    ),
                    SizedBox(height: 10,),
                    ProgressIcons(
                      total: pomodoroPerSet,
                      done: pomodoroNum - (setNum * pomodoroPerSet),
                    ),
                    SizedBox(height: 10,),
                    Text(
                      statusDescription[PomodoroStatus],
                    style: TextStyle(color: Colors.white),
                    ),
                    SizedBox(height: 10,),
                    CustomButton(
                        onTap: () {},
                        text: 'Start', ),
                    CustomButton(
                        onTap: () {},
                        text: 'Reset', )
                  ],

                ),
            ),
          ],),
        ),
      )
    );
  }
  _secondsToFormatedString(int seconds) {
    int roundedMinutes = seconds ~/60;
    int remainingSeconds = seconds - (roundedMinutes * 60);
    String remainingSecondsFormated;

    if (remainingSeconds < 10) {
      remainingSecondsFormated = '0$remainingSeconds';
    } else {
      remainingSecondsFormated = remainingSeconds.toString();
    }
    return '$roundedMinutes:$remainingSecondsFormated';
  }

  _mainButtonPressed() {
    switch(pomodoroStatus) {
      case PomodoroStatus.pausedPomodoro:
        _startPomodoroCountDown();
      break;
      case PomodoroStatus.runningPomodoro:
        // TODO: Handle this case.
        break;
      case PomodoroStatus.runningShortBreak:
        // TODO: Handle this case.
        break;
      case PomodoroStatus.pausedShortBreak:
        // TODO: Handle this case.
        break;
      case PomodoroStatus.runningLongBreak:
        // TODO: Handle this case.
        break;
      case PomodoroStatus.pausedLongBreak:
        // TODO: Handle this case.
        break;
      case PomodoroStatus.setFinished:
        // TODO: Handle this case.
        break;
    }
  }
  _startPomodoroCountDown() {
    pomodoroStatus = PomodoroStatus.runningPomodoro;

    _cancelTimer();
    
    _timer = Timer.periodic(Duration(seconds: 1), (timer) =>{
      if (remainingTime > 0) {
        setState((){
          remainingTime --;
          mainBtnText = _btnTextPause;
        })
      }
      else {
        //todo playSound(),
        pomodoroNum   ,
        _cancelTimer(),
        if (pomodoroNum % pomodoroPerSet == 0) {
          pomodoroStatus = PomodoroStatus.pausedLongBreak,
          setState((){
            remainingTime = lonBreakTime;
            mainBtnText = _btnTextStartLongBreak;
          }),
        } else {
          pomodoroStatus = PomodoroStatus.pausedShortBreak,
          setState((){
            remainingTime = shortBreakTime;
            mainBtnText = _btnTextStartShortBreak;
          }),
        }
      }
    });
  }

  _cancelTimer(){
    if (_timer != null) {
      _timer.cancel();
    }
  }
}

CodePudding user response：

The Text widget cannot be null. A string must first be given as a parameter.

71:40 --> Text(statusDescription[PomodoroStatus]) It does not accept because there is a possibility that the value may be empty on this line. If you're sure it's not empty, add a (!) to the end and you can continue. Text(statusDescription[PomodoroStatus]!)

CodePudding user response：

Solution:

Change:

statusDescription[PomodoroStatus]

to this:

statusDescription[pomodoroStatus]!

Explanation:

The Text widget expects a String and the result of statusDescription[pomodoroStatus] is nullable i.e is of type String?.

String? is not equivalent to String so you need to cast it to String by adding ! after the nullable variable.

Note:

Only use this if you're sure that statusDescription[pomodoroStatus] is not null.

If you're not sure, you can do a null-check and give a default variable if it is null.

Like this:

statusDescription[pomodoroStatus] ?? 'default status'