Flutter: Read File fails at the first time but works after Hot reload-CodePudding

I try to read a file where i have stored data and to show it on my screen. When I load my App for the first time i get the error shown bellow. After a hot reload my information will be displayed without any error. Do you know why this happens and how I can ensure that my data will be loaded already at the first time?

Maybe it has something to do with calling the state but I don't know. It is the code at the bottom which causes the problem:

child: Text(context.select((FileController controller) => controller.text!)),

import 'package:flutter/material.dart';
import 'package:habit_changer/file-handling/file_controller.dart';
import 'package:habit_changer/main/AddHabitDialog.dart';
import 'package:provider/provider.dart';
import '../utils/Constants.dart';
import 'MainBody.dart';
import 'nav_bar.dart';

void main() {
  runApp(MultiProvider(
    providers: [ChangeNotifierProvider(create: (_) => FileController())],
    child: MaterialApp(home: MyApp())
  ));
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    context.read<FileController>().readText();
    return Scaffold(
      appBar: AppBar(
        title: const Text('Habits'),
        backgroundColor: Constants.appBarColor,
        leading: GestureDetector(
          onTap: () {
            openNavBar();
          },
          child: Icon(
            Icons.menu, // add custom icons also
          ),
        ),
        actions: <Widget>[
          Padding(
            padding: EdgeInsets.only(right: 20.0),
            child: GestureDetector(
              onTap: () {
                showDialog(
                  context: context,
                  builder: (BuildContext context) =>
                      AddHabitDialog().buildPopupDialog(context),
                );
              },
              child: Icon(Icons.add),
            ),
          )
        ],
      ),
      body: Container(
        child: Text(context.select((FileController controller) => controller.text!)),
      ),
    );
  }
}

Here's the error:

Null check operator used on a null value

The relevant error-causing widget was: 
  MyApp file:///C:/Projekte/Flutter Projects/habit_changer/lib/main/main.dart:13:30
When the exception was thrown, this was the stack: 
#0      MyApp.build.<anonymous closure> (package:habit_changer/main/main.dart:52:82)
#1      SelectContext.select (package:provider/src/inherited_provider.dart:283:32)
#2      MyApp.build (package:habit_changer/main/main.dart:52:29)
#3      StatelessElement.build (package:flutter/src/widgets/framework.dart:4648:28)
#4      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4574:15)

CodePudding user response：

This can happen when your variable is null initially but then receives the value later on. Change the operator to a null check operator:

controller.text ?? ''

This will solve the null exception that you are receiving.