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Lessons learned

📘 Table of Contents

How to add support to localization

Localization (l10n) and Internationalization (i18n) are handled by flutter_localizations and intl official flutter packages. Configure the project like in https://docs.flutter.dev/ui/accessibility-and-internationalization/internationalization.

To add a localized string, add it to all the .arb files inside the lib\l10n directory, and reference it using AppLocalizations.of(context)!.<FIELD_NAME> from code.

Override the system locale using the Localizations.override widget.

How to add a custom annotation with code generation

We'll use the build_runner dart package to do so.

  1. In pubspec.yaml:
dependencies:
  source_gen: ^2.0.0

dev_dependencies:
  build_runner: ^2.4.7
  build: ^2.4.2
  analyzer: ^7.1.0
  1. Add the annotation class and the code generator class, just like I did in this project, in the annotation/ folder. Make sure to add the builder method in the generator file.
  2. Add a build.yaml file in the project root and register the newly created generator:
builders:
  scheda_dnd_5e|localized:
    import: "package:scheda_dnd_5e/annotation/generator/localized_generator.dart"
    builder_factories: [ "localizedGenerator" ]
    build_extensions: { ".dart": [ ".g.dart" ] }
    auto_apply: dependents
    build_to: source

targets:
  $default:
    builders:
      scheda_dnd_5e|localized:
        generate_for:
          - lib/**/*.dart
  1. Use dart run build_runner build to run the generator. This will create a .g.part file. Change the extension to .dart to highlight any syntax error.

Note: this approach uses the extension functions mechanism, so you need to import the generated file where you need to access it. Another way to go is to use the part/part-of dart mechanism.

Emulator is unbearably glitchy

Problem

When GPU is in use (host mode) the emulator is faster, but more glitchy, the app crashes often and screen sometimes freezes, preventing alert dialogs from showing.

Solution

Device Manager --> 3 dots --> Show on Disk --> open config.ini --> edit hw.gpu.mode from host to guest to disable GPU optimization --> Stop and run device with Cold boot.

As it's always the case, CPU is slower but safer when it comes to emulation.

Undo Github commits

Problem

Sometimes you need to remove the latest commits from Github. This happens, for example, in the case of a large merge operation caused by a forgotten `fetch' before committed changes.

Solution

From the terminal, launch the following commands:

  1. git reset --soft <COMMIT_HASH> where COMMIT_HASH is the SHA of the commit you can retrieve from Github or through the git rev-list HEAD command.
    • --soft is used to move the HEAD position updating the index, but not the working tree, i.e. the local files.
    • --hard is used to move the HEAD position updating the index and the working tree.
  2. git add . & git commit -m <MSG> to commit the working tree.
  3. git push origin <BRANCH> --force to overwrite all the commits happened after the COMMIT_HASH.

Git mismatching line ending causes huge commits

Problem

When committing from Linux, git forced me to rewrite all the files in the project, even those without any changes by my side.

Solution

This is due to the value of the core.autocrlf git variable, which may be different between my Windows and Linux installations. This cause git to overwrite the LF with CRLF. The solution is to write * text=auto in the .gitattributes file in the root of the project.

Read more here.

View components taxonomy

  • page: A widget wrapped with a Material. Note that Scaffold implicitly defines it.
  • screen: A collection of widgets defining the content of a page or a portion of it. Does not define a parent Material, thus, must be inside a page.
  • partial: A customizable widget or layout that is reused throughout the application. Specialize Flutter's built-in components to the needs of the application. Minimize the client's freedom in the parameters.

Pass arguments to a page

Problem

When calling a polymorphous page, how should I pass my arguments?

Solution

I can come up with two strategies. In both case it's best to wrap our arguments in a dedicate class.

Navigator's arguments

As in Flutter Doc, one way is to rely on Navigator's raw form of dependency injection.

ValueNotifier<Args?> args = ValueNotifier(null);

// build()
args.value ??= (
ModalRoute.of(context)!.settings.arguments) as Args?;

// initState()
args.addListener(() {
// Required to ensure that the widgets are built (may not be needed)
WidgetsBinding.instance.addPostFrameCallback((_) {
// Any initialization that needs to know the value of the args
});
});

The advantage is a loosely coupled binding between the caller and the page.

Note: if you split the polymorphous widget into page + screen, the page receives the args from the Navigator and passes them to the screen constructor. This way the ValueNotifier<> wrapper can be removed and the screen code becomes:

final Args? args;

// initState()
WidgetsBinding.instance.addPostFrameCallback
(
(_) {
// Any initialization that needs to know the value of the args
});

Using the constructor

This approach ties the navigation logic with the page's constructor. It should be used only on partials and screens.

Java and Gradle Compatibility

Problem

Application fails to launch due to incompatibility between Java and Gradle version.

Solution

  1. Check versions according to Compatibility Matrix
    • Determine Gradle version by checking the distributionUrl in the android/gradle/wrapper/gradle-wrapper.properties file.
    • Verify Java version by running java -version in terminal.
  2. If Java version is incompatible, change it with:
flutter config --jdk-dir <path_to_jdk>
  1. Recreate Project (if Gradle and Java versions are compatible)
    • Delete the android folder.
    • Recreate the project using:
flutter create --project-name scheda_dnd_5e .

Note: JDK version is your degree of freedom, flutter manages its own version of Gradle.

Use [] initialization when the list is involved in a generic usage

When working with generics, it may become tricky to handle the assignment to lists.

Problem

List<Character>? cachedCharacters = null;
List<Enchantment>? cachedEnchantments = null;

Map<core.Type, List<WithUID>> get caches =>
    {
      Character: cachedCharacters,
      Enchantment: cachedEnchantments,
    };

In this scenario, assigning the empty list is no easy task if we access the variable through caches, where the supertype is WithUID. This is because, in an instruction like cache[Chracter]! = [] we try to assign List<WithUID> to List<Chracter>.

Solution

List<InventoryItem> cachedInventoryItems = [];