Flutter: Use setState in a function?

Question

is there any way I can use setState() in a function (line 26)? I am trying to call the function item (which includes the setState) from my main.dart file and Flutter doesn't like that. Also, the item function is in a different file than the main.dart. Can someone please help me?

item function:

    item(itemName, color, itemVariable) {
  return Container(
    color: color ? Colors.grey[200] : Colors.white,
    child: Row(
      children: [
        Flexible(
          child: Padding(
            padding: const EdgeInsets.all(8.0),
            child: Text(
              "${itemVariable}x",
              style: const TextStyle(fontSize: 25),
            ),
          ),
        ),
        Text(
          itemName,
          style: const TextStyle(fontSize: 25),
        ),
        Flexible(
          child: Padding(
            padding: const EdgeInsets.fromLTRB(30, 5, 0, 10),
            child: TextField(
              onSubmitted: (value) {
                itemVariable = int.parse(value);
                print("Hodnota pro ${itemName} nastavena na: ${itemVariable}");
                setState(() {});
              },
              keyboardType: TextInputType.number,
              decoration: InputDecoration(
                filled: true,
                enabledBorder: OutlineInputBorder(
                  borderRadius: BorderRadius.circular(15),
                  borderSide: const BorderSide(color: Colors.blue),
                ),
                focusedBorder: OutlineInputBorder(
                  borderRadius: BorderRadius.circular(15),
                  borderSide: const BorderSide(color: Colors.blue, width: 2),
                ),
              ),
            ),
          ),
        ),
      ],
    ),
  );
}

main.dart file:

import 'package:flutter/material.dart';
import 'package:intr_obleceni/items.dart';
import 'package:intr_obleceni/functions.dart';

void main() => runApp(
      const MaterialApp(
        home: Main(),
        title: "Intr - seznam oblečení",
      ),
    );

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

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

class _MainState extends State<Main> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text("Internát - seznam oblečení"),
        elevation: 2,
      ),
      body: ListView(
        children: [
          category("Bundy", false),
          item("Bunda", false, Bundy.bunda),
          item("Softčílová bunda", false, Bundy.softcilovaBunda),
          category("Ostatní", true),
          item("Ručník", true, Ostatni.rucnik)
        ],
      ),
    );
  }
}

could you post the other dart file as well

flutterloop
– flutterloop

2022-02-23 21:00:24 +00:00
Commented Feb 23, 2022 at 21:00 — flutterloop
– flutterloop, Commented Feb 23, 2022 at 21:00

Francis Nduba Numbi · Accepted Answer · 2022-02-23 21:32:40Z

2

instead of calling the setState() function in your function, include a callback function in your params like this :

item(itemName, color, itemVariable {Function? callback}) {

// where you used setState(), use callback()
}

then in your main.dart file, where you called that item function, wrap setState in the callback function.

answered Feb 23, 2022 at 21:32

Francis Nduba Numbi

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4 Comments

DavidCZ2051 Over a year ago

But I am not calling setState() in my main.dart. Could you please provide an example?

Francis Nduba Numbi Over a year ago

Inside listview, you called item(), that is the item() function, when you set callback() function as one of your params, you can easily place setStat() inside

DavidCZ2051 Over a year ago

It says: "This expression has a type of 'void' so its value can't be used. Try checking to see if you're using the correct API; there might be a function or call that returns void you didn't expect. Also check type parameters and variables which might also be void." when i put setState() in the item function.

Csaba Mihaly Over a year ago

you call item("Bunda", false, Bundy.bunda, setState) and you only need to add Function callback without ? and {}

KyleDev · Accepted Answer · 2023-07-21 12:39:41Z

For those that still need an answer to this, here's what worked for me:

The safest bet is going to be to instead of using a function, to rather use a class based on the StatefulWidget class. My implementation went something like this:

class MyClass extends StatefulWidget {
    final SomeType someVariable1;
    final SomeType someVariable2;
    final SomeType someVariable3;

    const MyClass({
        required this.someVariable1,
        required this.someVariable2,
        required this.someVariable3,
        super.key,
    });

    @override
    State<MyClass> createState() => _MyClassState();

class _MyClassState extends State<MyClass> {
    @override
    Widget build(BuildContext context) {
    return SomeWidget(
        // you can call setState() here as needed.
        );
    }

This should allow you to call setState() as much as you need to within the widget that you were generating within your item.

The class can also then be placed into another file without causing any issues.

Hope this helps someone out somewhere.

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