Question 74940 in Flutter Question posted in
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When I assign a formKey and return a query, I get a null error – Flutter

I’m doing a validation process, but I want to do it between different pages. How can I perform the validate process on another page using formKey or another solution? I’m getting a null error, how do I get rid of it?

my main file is below

import 'package:flutter/material.dart';
import 'package:intl_flutter_deneme/buton.dart';
import 'package:intl_phone_number_input/intl_phone_number_input.dart';
import 'package:mask_text_input_formatter/mask_text_input_formatter.dart';
import 'package:share_plus/share_plus.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(primarySwatch: Colors.amber),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({super.key});

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  TextEditingController phoneController = TextEditingController();
  bool isButtonActive = false;
  final _formKey = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('phone number settings'),
      ),
      body: Center(
        child: Column(
          children: [
            Form(
              key: _formKey,
              child: InternationalPhoneNumberInput(
                countries: ['TR'],
                onInputChanged: (PhoneNumber number) {
                  print(number.phoneNumber);
                },
                maxLength: 13,
                hintText: '5## ### ## ##',
                validator: (deger) {
                  if(deger!.isEmpty && deger.length < 13) {
                    return 'doğru şekilde numara gir';
                  }return null;
                },
                spaceBetweenSelectorAndTextField: 0,
                inputDecoration: InputDecoration(),
                textFieldController: phoneController,
              ),
            ),
            ButonIslemi(),
                
            ElevatedButton(
                onPressed: sharedMessage, child: Text('share')),
          ],
        ),
      ),
    );
  }

  void sharedMessage() {
    String message = 'https://www.instagram.com/atakansever_/';
    Share.share(message);
  }
}

The part that performs the validation when the button is pressed is below

import 'package:flutter/material.dart';
import 'package:intl_flutter_deneme/main.dart';

class ButonIslemi extends StatelessWidget {
  ButonIslemi({super.key});
  final formKey = GlobalKey<FormState>();
  @override
  Widget build(BuildContext context) {
    return ElevatedButton(onPressed: () {
      if(formKey.currentState!.validate()) {
        print('işlem başarılı');
      }
    }, child: Text('bas'));
  }
}

The error I get when pressing the button is as follows

enter image description here

Tags:

2

Answers


  1. 0

    You should move your _formKey definition outside _MyHomePageState and make it public:

    formKey = Global<FormState>()

    And then use the same formKey in both Form and ButonIslemi instead of instantiate a new key in ButonIslemi.

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  2. 0

    You can send _formkey as parameter with button and use same key for button

    @override
Widget build(BuildContext context) {
return Scaffold(
  appBar: AppBar(
    title: Text('phone number settings'),
  ),
  body: Center(
    child: Column(
      children: [
        Form(
          key: _formKey,
          child: InternationalPhoneNumberInput(
            countries: ['TR'],
            onInputChanged: (PhoneNumber number) {
              print(number.phoneNumber);
            },
            maxLength: 13,
            hintText: '5## ### ## ##',
            validator: (deger) {
              if(deger!.isEmpty && deger.length < 13) {
                return 'doğru şekilde numara gir';
              }return null;
            },
            spaceBetweenSelectorAndTextField: 0,
            inputDecoration: InputDecoration(),
            textFieldController: phoneController,
          ),
        ),
        ButonIslemi(_formKey),
        ElevatedButton(onPressed: sharedMessage, child: Text('share')),
      ],
    ),
  ),
);
}

    And here is button

    class ButonIslemi extends StatelessWidget {
   GlobalKey<FormState> _formKey;
   ButonIslemi(this._formKey, {super.key});
   @override
   Widget build(BuildContext context) {
      return ElevatedButton(onPressed: () {
       if(_formKey.currentState!.validate()) {
       print('işlem başarılı');
      }
    }, 
    child: Text('bas'));
  }
}
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