angular - 工厂提供者可以有可选的依赖吗？

Question

例如:

@NgModule ({
  providers: [ 
    { provide: MyService, 
      useFactory: (optionalDep) => new MyService(optionalDep)
      deps: [SOME_DEP]
    }
})
class MyModule {}

useFactory 可以有可选的依赖吗？

Answer 1

根据官方文档，您可以执行以下操作:

const Location = new InjectionToken('location');
const Hash = new InjectionToken('hash');

const injector = Injector.create([{
  provide: Hash,
  useFactory: (location: string) => `Hash for: ${location}`,
  // use a nested array to define metadata for dependencies.
  deps: [[new Optional(), Location]]
}]);

expect(injector.get(Hash)).toEqual('Hash for: null');

参见 https://angular.io/api/core/FactoryProvider#example更多