Flutter mobx mobx_codegen generates null safety code for computed getters - flutter

Question

Using mobx and mobx_codegen for Flutter.
My code is NOT null safe (sdk: ">=2.7.0 <3.0.0").
When mobx_codegen generates code for #computed getters, it uses null safety, which won't compile...
Sample class counter (look at #computed):
import 'package:mobx/mobx.dart';
// Include generated file
part 'counter.g.dart';
// This is the class used by rest of your codebase
class Counter = _Counter with _$Counter;
// The store-class
abstract class _Counter with Store {
#observable
int value = 0;
#computed
int get test => 0;
#action
void increment() {
value++;
}
}
Relevant generated code (counter.g.dart):
Computed<int>? _$testComputed;
Shows this error:
This requires the 'non-nullable' language feature to be enabled.
Try updating your pubspec.yaml to set the minimum SDK constraint to 2.12.0 or higher, and running 'pub get'.
I'm new to mobx, am I doing something wrong?

Answer 1

How´s it going?
I am with the same issue in my project. I installed the new flutter version and after that my project stopped to compile. I changed my dependences of mobx, flutter_mobx, mobx_codegen and build_runner and them worked.
My first dependences:
mobx: ^1.2.1+4
flutter_mobx: ^1.1.0+2
build_runner: ^1.11.5
mobx_codegen: ^1.1.2
My last dependences:
mobx: ^2.0.6+1
flutter_mobx: ^2.0.4
build_runner: ^2.1.7
mobx_codegen: ^2.0.5+2
From there, It has started my issue of "#computed" while I run the build_runner.
I changed the Dart SDK of my project and It stopped to show error of "#computed". But broke all source code because I developed my code with "non- null-safety".
So, looking for replies. I figured out the root cause is the specifically the mobx_codegen newer dependency that uses null safety and doesn´t have a tratament to valid our Dart SDK.
In my opnion, It should´ve validated while running of build_runner.
So, Someone knows how could I resolve that issue?
I have a commercial solution of app, and I´ve planned to release until 3 months.
my pubspec.yaml is so:
name: XPTO
description: A new Flutter project.
# The following line prevents the package from being accidentally published to
# pub.dev using `flutter pub publish`. This is preferred for private packages.
publish_to: 'none' # Remove this line if you wish to publish to pub.dev
# The following defines the version and build number for your application.
# A version number is three numbers separated by dots, like 1.2.43
# followed by an optional build number separated by a +.
# Both the version and the builder number may be overridden in flutter
# build by specifying --build-name and --build-number, respectively.
# In Android, build-name is used as versionName while build-number used as versionCode.
# Read more about Android versioning at https://developer.android.com/studio/publish/versioning
# In iOS, build-name is used as CFBundleShortVersionString while build-number used as CFBundleVersion.
# Read more about iOS versioning at
# https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
version: 1.0.0+1
environment:
sdk: ">=2.7.0 <3.0.0"
# Dependencies specify other packages that your package needs in order to work.
# To automatically upgrade your package dependencies to the latest versions
# consider running `flutter pub upgrade --major-versions`. Alternatively,
# dependencies can be manually updated by changing the version numbers below to
# the latest version available on pub.dev. To see which dependencies have newer
# versions available, run `flutter pub outdated`.
dependencies:
flutter:
sdk: flutter
# The following adds the Cupertino Icons font to your application.
# Use with the CupertinoIcons class for iOS style icons.
cupertino_icons: ^1.0.2
mobx: ^2.0.6+1
flutter_mobx: ^2.0.4
get_it: ^7.2.0
flutter_search_bar: ^3.0.0-dev.1
carousel_slider: ^4.0.0
intl: ^0.17.0
image_picker: ^0.8.4+5
image_cropper: ^1.4.1
parse_server_sdk_flutter: ^3.1.0
cpf_cnpj_validator: ^2.0.0
brasil_fields: ^1.3.0
mask_text_input_formatter: ^2.1.0
badges: ^2.0.2
flutter_rating_bar: ^4.0.0
expandable: ^5.0.1
flutter_easyloading: ^3.0.3
internet_connection_checker: ^0.0.1+3
cached_network_image: ^3.2.0
flutter_keyboard_visibility: ^5.1.1
json_annotation: ^4.4.0
dev_dependencies:
flutter_test:
sdk: flutter
build_runner: ^2.1.7
mobx_codegen: ^2.0.5+2
graphs: ^2.1.0
json_serializable: ^6.1.4
dependency_overrides:
plugin_platform_interface: ^2.0.0
build_resolvers: ^2.0.6
web_socket_channel: ^2.0.0
analyzer: ^3.2.0
# The "flutter_lints" package below contains a set of recommended lints to
# encourage good coding practices. The lint set provided by the package is
# activated in the `analysis_options.yaml` file located at the root of your
# package. See that file for information about deactivating specific lint
# rules and activating additional ones.
flutter_lints: ^1.0.0
# For information on the generic Dart part of this file, see the
# following page: https://dart.dev/tools/pub/pubspec
# The following section is specific to Flutter.
flutter:
# The following line ensures that the Material Icons font is
# included with your application, so that you can use the icons in
# the material Icons class.
uses-material-design: true
# To add assets to your application, add an assets section, like this:
# assets:
# - images/a_dot_burr.jpeg
# - images/a_dot_ham.jpeg
assets:
- images/logo.jpeg
- images/empty.jpg
# An image asset can refer to one or more resolution-specific "variants", see
# https://flutter.dev/assets-and-images/#resolution-aware.
# For details regarding adding assets from package dependencies, see
# https://flutter.dev/assets-and-images/#from-packages
# To add custom fonts to your application, add a fonts section here,
# in this "flutter" section. Each entry in this list should have a
# "family" key with the font family name, and a "fonts" key with a
# list giving the asset and other descriptors for the font. For
# example:
# fonts:
# - family: Schyler
# fonts:
# - asset: fonts/Schyler-Regular.ttf
# - asset: fonts/Schyler-Italic.ttf
# style: italic
# - family: Trajan Pro
# fonts:
# - asset: fonts/TrajanPro.ttf
# - asset: fonts/TrajanPro_Bold.ttf
# weight: 700
#
# For details regarding fonts from package dependencies,
# see https://flutter.dev/custom-fonts/#from-packages

Answer 2

Since you're using a version of MobX that has null-safety, you can either:
migrate your code to null-safety (recommended).
downgrade your mobx, mobx_codegen and build_runner packages to a version that doesn't have null-safety.
To migrate your code, you can follow this Migration Guide.
If you opt to downgrade, be aware that you might run into version conflicts and there's a chance you have to downgrade your Flutter SDK too.