List does not appear in the app interface - flutter

Question

The idea is that a list appears on my app screen and is updated as I add texts to the textField, but in my tests the list appears empty even though I put test items there.
image error
flutter version 1.0.0
dependences
path_provider: ^1.1.0
code atualization
import 'package:flutter/material.dart';
import 'package:path_provider/path_provider.dart';
import 'dart:io';
import 'dart:async';
import 'dart:convert';
class Home extends StatefulWidget {
#override
_HomeState createState() => _HomeState();
}
class _HomeState extends State<Home> {
List _listaTarefas = [];
Future<File> _pegarArquivo() async {
final diretorio = await getApplicationDocumentsDirectory();
return File("${diretorio.path}/dados.json");
}
_salvarArquivo() async {
var arquivo = await _pegarArquivo();
Map<String, dynamic> tarefa = Map();
tarefa['titulo'] = "Teste";
tarefa['realizada'] = false;
_listaTarefas.add(tarefa);
String dados = json.encode(_listaTarefas);
arquivo.writeAsString(dados);
}
_lerArquivo() async {
try {
final arquivo = await _pegarArquivo();
return arquivo.readAsString();
} catch (e) {
return null;
}
}
#override
void initState() {
super.initState();
_lerArquivo().then((dados) {
setState(() {
_listaTarefas = json.decode(dados);
});
});
}
#override
Widget build(BuildContext context) {
_salvarArquivo();
print('Resultado' + _listaTarefas.toString());
return Scaffold(
appBar: AppBar(
title: Text('Lista de tarefas'),
backgroundColor: Colors.purple,
),
floatingActionButtonLocation: FloatingActionButtonLocation.endFloat,
floatingActionButton: FloatingActionButton(
child: Icon(Icons.add),
backgroundColor: Colors.purple,
onPressed: () {
showDialog(
context: context,
builder: (context) {
return AlertDialog(
title: Text('Adicionar Tarefa'),
content: TextField(
decoration: InputDecoration(
labelText: 'Digite sua tarefa',
),
onChanged: (text) {},
),
actions: <Widget>[
FlatButton(
onPressed: () => Navigator.pop(context),
child: Text('cancelar'),
),
FlatButton(
onPressed: () {
Navigator.pop(context);
},
child: Text('Salvar'),
),
],
);
});
}),
body: Column(
children: <Widget>[
Expanded(
child: ListView.builder(
itemCount: _listaTarefas.length,
itemBuilder: (context, index) {
return ListTile(
title: Text(_listaTarefas[index]['titulo']),
);
}))
],
),
);
}
}

Answer 1

The problem
When you declare the following method
_lerArquivo() async {
try {
final arquivo = await _pegarArquivo();
return arquivo.readAsStringSync();
} catch (e) {
return Text('erro');
}
}
you're returning a String when you do
return arquivo.readAsStringSync();
and a Text when you do
return Text('erro');
The solution
To fix this, you can either
return a string in the second return:
_lerArquivo() async {
try {
final arquivo = await _pegarArquivo();
return arquivo.readAsStringSync();
} catch (e) {
return 'erro';
}
}
do nothing:
_lerArquivo() async {
final arquivo = await _pegarArquivo();
return arquivo.readAsStringSync();
}
The good practice
To avoid future errors (i.e. transform run-time errors into compile-time errors), declare your variable types, return types and type parameters explicitely:
String _lerArquivo() async {
try {
final arquivo = await _pegarArquivo();
return arquivo.readAsStringSync();
} catch (e) {
// ...
}
}