AngularDart与Flutter共享代码：AppController依赖注入疑问

Hey there! Let's break down your questions step by step since you're working on a shared codebase between AngularDart and Flutter—smart move reusing business logic across frameworks!

AngularDart: Do you need @Injectable()? #

Short answer: It's strongly recommended, especially for classes with constructor dependencies like your AppController.

AngularDart's DI system can resolve simple classes without @Injectable() in some cases, but marking your controllers and services with @Injectable() eliminates edge cases and makes your intent clear. For example:

• If your AppController or services have multiple constructors, Angular needs @Injectable() to know which one to use for injection.
• If you ever swap a concrete service with an abstract class (e.g., AbstractServiceOne instead of ServiceOne), @Injectable() becomes mandatory to help DI resolve the implementation.

Here's how your shared AppController should look for AngularDart:

import 'package:angular/angular.dart';

@Injectable()
class AppController {
  final ServiceOne serviceOne;
  final ServiceTwo serviceTwo;

  // Constructor injection works seamlessly with @Injectable()
  AppController(this.serviceOne, this.serviceTwo);
}

// Don't forget to mark your services too!
@Injectable()
class ServiceOne {}

@Injectable()
class ServiceTwo {}

Then register them in your AngularDart bootstrap:

void main() {
  bootstrap(AppComponent, [
    AppController,
    ServiceOne,
    ServiceTwo,
  ]);
}

Flutter: Handling DI for shared code #

You're right—Flutter doesn't have a built-in DI system like AngularDart, but that doesn't mean you can't reuse your shared AppController and services. The key is to keep your shared code framework-agnostic.

Best practice: Keep shared classes "pure" #

Avoid adding AngularDart-specific annotations (like @Injectable()) directly to your shared code if you can. Instead, use one of these approaches:

1. Conditional imports: Only apply @Injectable() when compiling for AngularDart. Example:

   // shared/app_controller.dart
   class AppController {
     final ServiceOne serviceOne;
     final ServiceTwo serviceTwo;
   
     AppController(this.serviceOne, this.serviceTwo);
   }
   
   // angular/app_controller.injectable.dart
   import 'package:angular/angular.dart';
   import '../shared/app_controller.dart';
   
   @Injectable()
   class AppController extends SharedAppController {}
   

2. Use Flutter community DI packages: Tools like provider, riverpod, or get_it work perfectly with pure Dart classes. For example, with get_it:

   // Flutter setup
   final getIt = GetIt.instance;
   
   void setupDI() {
     // Register singleton instances of your services
     getIt.registerSingleton<ServiceOne>(ServiceOne());
     getIt.registerSingleton<ServiceTwo>(ServiceTwo());
     // Inject dependencies into AppController
     getIt.registerSingleton<AppController>(AppController(getIt(), getIt()));
   }
   

   Then access AppController in your Flutter widgets:

   final appController = getIt<AppController>();
   

Final takeaways #

• For AngularDart: Always mark injectable classes with @Injectable() to avoid DI headaches down the line.
• For cross-framework compatibility: Keep your core business logic (controllers, services) as pure Dart classes with no framework-specific dependencies.
• Flutter DI: Use community packages to wire up your shared classes—they're lightweight and play nicely with pure Dart code.

内容的提问来源于stack exchange，提问作者Augie Li