form reset() function gives null pointer for a dropdownmenu with onChange=null

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We have a DropdownButtonFormField which we have disabled by setting the onChanged to null. This works fine as the look and feel of the widget show a disabled state and the user cannot change the value. I just figured out that we can also set the items to null and use the disabledHint property so I am not sure if setting onChanged to null is a "valid" way of disabling a DropdownButtonFormField.

Once the user is done submitting the form we reset it using a GlobalKey

final _formKey = GlobalKey(debugLabel: '_ClientEditState');

and call the reset() function on the formState like so:

_formKey.currentState?.reset()

This triggers a reset() on all form fields but on a DropdownButtonFormField without a onChanged it creates a NPE.

This is because of the following line of code in the dropdown reset() function:
_dropdownButtonFormField.onChanged!(value);

As onChanged can be null (and it seems also that this can be intended behaviour to disable the widget because the widget becomes disabled) there should be a null check around this call.

Thanks for the report.

Code sample for repro

import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Example(),
    );
  }
}

class Example extends StatelessWidget {
  final _formKey = GlobalKey<FormState>();
  Example({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Form(
        key: _formKey,
        child: Column(
          children: [
            DropdownButtonFormField(
              items: const [
                DropdownMenuItem(
                  value: "item1",
                  child: Text("item1"),
                )
              ],
              onChanged: null,
            ),
            ElevatedButton(
              onPressed: () {
                _formKey.currentState?.reset();
              },
              child: const Text("reset"),
            ),
          ],
        ),
      ),
    );
  }
}

Fix DropdownButtonFormField throws when onChange is null (#146342)

Fix DropdownButtonFormField throws when onChange is null (flutter#146342

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Fix DropdownButtonFormField throws when onChange is null (#146342)

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form reset() function gives null pointer for a dropdownmenu with onChange=null #146335

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form reset() function gives null pointer for a dropdownmenu with onChange=null #146335

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bleroux commented on Apr 5, 2024

github-actions commented on Apr 22, 2024

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