Do I need to use [providers] when implementing constructor dependency injection?

Question

Do I need to use [providers] when implementing constructor dependency injection?

Currently following a step-by-step guide on managing tasks and it includes the following code snippet:

 import {TodoDataService} from './todo-data.service';

 @Component({
  // ...
   providers: [TodoDataService]
 })

 constructor(private todoDataService: TodoDataService) {
 }

It appears that we need to declare the TodoDataService in the providers array. This feels repetitive. Is there a way for Angular's Dependency Injection to automatically recognize the component's metadata and inject the TodoDataService through the constructor?

Update

Angular seems to have made some progress in this area according to certain sources. I even suggested that they eliminate providedIn:root and they mentioned having plans for that in their future updates.

angular typescript angular-decorator

Answer 1

Answer №1

According to the documentation on Angular.io:

Injector bubbling

When a component requests a dependency, Angular will first look for a provider registered in that component's own injector. If the provider is not found, it will move up to the parent component's injector. This process continues up the component tree until Angular finds a suitable provider or exhausts all ancestor injectors, resulting in an error.

From my understanding, this means that each component will have its own instance of a service if it provides one. Otherwise, Angular will search up the component hierarchy until it finds a provider. Ultimately, a service must be provided somewhere in the application.

Even though Angular considers the metadata to determine the service a component needs, the `providers:[TodoDataService]` statement is crucial for defining where the service comes from.

In my experience, I typically provide most services in my `app.module.ts` file to ensure that each service is a singleton throughout the entire application.

Answer 2

According to the documentation on Angular.io:

Injector bubbling

When a component requests a dependency, Angular will first look for a provider registered in that component's own injector. If the provider is not found, it will move up to the parent component's injector. This process continues up the component tree until Angular finds a suitable provider or exhausts all ancestor injectors, resulting in an error.

From my understanding, this means that each component will have its own instance of a service if it provides one. Otherwise, Angular will search up the component hierarchy until it finds a provider. Ultimately, a service must be provided somewhere in the application.

Even though Angular considers the metadata to determine the service a component needs, the `providers:[TodoDataService]` statement is crucial for defining where the service comes from.

In my experience, I typically provide most services in my `app.module.ts` file to ensure that each service is a singleton throughout the entire application.

Do I need to use [providers] when implementing constructor dependency injection?

Update

Answer №1

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