How to add element to an already existing list from another class?

Question

I want to make a todo-list app with flutter, but I'm having trouble saving the text input, to the list already created in another class that I display.

I have tried creating an object in the other class with a setter but since I'm using a stateful widget, that won't work, especially because I am using Lists() (a list view) on the body of the scaffold to display the list items

this is my list view class

import 'package:flutter/material.dart';
import 'todo.dart';

class TodoListS extends StatefulWidget {
  @override
  TodoList createState() => TodoList();
}
 class TodoList extends State<TodoListS> {
   List<Todo> todos = [Todo(title:'Checktheicon'), Todo(title: 'help me')];
   void setTodo(Todo todo)
   {
     todos.add(todo);
   }
      @override
      Widget build(BuildContext context) {

        return myListView(context,todos );
      }
    }

Widget myListView(BuildContext context, List<Todo> todos) {

      // backing data

      return ListView.builder(
        itemCount: todos.length,
        itemBuilder: (context, index) {
          return ListTile(
            title: Text(todos[index].title),
            leading: Icon(todos[index].icons),
          );
        },
      );

    }

This is where I display the list

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
          backgroundColor: Colors.pink[100], title: new Text('Todo List')),
      body: TodoListS(),
      floatingActionButton: FloatingActionButton(
          child: Icon(Icons.add), onPressed: () =>  _displayDialog(context)),
    );
  }

This is where I want to get the text input and save it

_displayDialog(BuildContext context) {
      return showDialog(
          context: context,
          builder: (context) {
            return AlertDialog(
              title: Text('Insert Your to do'),
              content: TextField(
                controller: _textFieldController,
                decoration: InputDecoration(hintText: "ie. Wash dishes"),
              ),
              actions: <Widget>[
                new FlatButton(
                  child: new Text('CANCEL'),
                  onPressed: () {
                    Navigator.of(context).pop();
                  },
                ),
                new FlatButton(
                  child: new Text('ADD'),
                  onPressed: () {
                  var todo = new Todo(title: _textFieldController.value.text);
                  todol.setTodo(todo);
                    Navigator.of(context).pop();
                  },
                )
              ],
            );
          });
    }

So right now , nothing is getting saved, the only thing being displayed are my previously created todo, the my text input need to be added to the list so that it can be displayed.

Answer 1

To call function in another class, you can use GlobalKey

Step 1: define final GlobalKey<TodoList> _key = GlobalKey();
Step 2: In onPressed use _key.currentState.setTodo(Todo(title: _textFieldController.text));
Step 3: Add key to class

class TodoListS extends StatefulWidget {
  TodoListS({Key key}) : super(key: key);

Step 4: TodoListS pass key

body: TodoListS(
        key: _key,
      ),

full working code

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final _textFieldController = TextEditingController();
  final GlobalKey<TodoList> _key = GlobalKey();

  @override
  void dispose() {
    // Clean up the controller when the widget is removed from the
    // widget tree.
    _textFieldController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar:
          AppBar(backgroundColor: Colors.pink[100], title: Text('Todo List')),
      body: TodoListS(
        key: _key,
      ),
      floatingActionButton: FloatingActionButton(
          child: Icon(Icons.add), onPressed: () => _displayDialog(context)),
    );
  }

  _displayDialog(BuildContext context) {
    return showDialog(
        context: context,
        builder: (context) {
          return AlertDialog(
            title: Text('Insert Your to do'),
            content: TextField(
              controller: _textFieldController,
              decoration: InputDecoration(hintText: "ie. Wash dishes"),
            ),
            actions: <Widget>[
              FlatButton(
                child: Text('CANCEL'),
                onPressed: () {
                  Navigator.of(context).pop();
                },
              ),
              FlatButton(
                child: Text('ADD'),
                onPressed: () {
                  /*var todo =  Todo(title: _textFieldController.value.text);
                  todol.setTodo(todo);*/

                  _key.currentState
                      .setTodo(Todo(title: _textFieldController.text));
                  setState(() {

                  });
                  Navigator.of(context).pop();
                },
              )
            ],
          );
        });
  }
}

class Todo {
  String title;

  Todo({
    this.title,
  });

  factory Todo.fromJson(Map<String, dynamic> json) => Todo(
        title: json["title"] == null ? null : json["title"],
      );

  Map<String, dynamic> toJson() => {
        "title": title == null ? null : title,
      };
}

class TodoListS extends StatefulWidget {
  TodoListS({Key key}) : super(key: key);
  @override
  TodoList createState() => TodoList();
}

class TodoList extends State<TodoListS> {
  List<Todo> todos = [Todo(title: 'Checktheicon'), Todo(title: 'help me')];

  void setTodo(Todo todo) {
    todos.add(todo);
  }

  @override
  Widget build(BuildContext context) {
    return myListView(context, todos);
  }
}

Widget myListView(BuildContext context, List<Todo> todos) {
  // backing data
  return ListView.builder(
    itemCount: todos.length,
    itemBuilder: (context, index) {
      return ListTile(
        title: Text(todos[index].title),
        //leading: Icon(todos[index].icons),
      );
    },
  );
}

full working demo