In this tutorial we are going to see how to use dependency injection in angular to imporve the modularity , the readability and the maintenability of the project.
Table of Contents
What is a Dependency in Angular ?
In Angular, a dependency is a service or object that a component or service requires in order to work properly.
Dependencies are typically injected into a component or service through a constructor, using the dependency injection framework provided by Angular.
For example, if a component needs to access a service that performs some specific task, such as fetching data from a server, that service would be considered a dependency of the component.
What is Dependency Injection in Angular ?
Dependency injection is a design pattern that allows an Angular component or service to receive its dependencies from an external source, rather than creating them itself.
This allows components and services to be more modular and testable, as they are not tied to a specific implementation of their dependencies.
Dependency injection in Angular is achieved through the use of a dependency injection framework, which provides a way to register dependencies and inject them into components and services.
When a component or service is instantiated, the dependency injection framework looks for any dependencies that are required by the constructor and injects them automatically.
How to use Dependency Injection in Angular ?
To use dependency injection in Angular, you need to follow these steps:
Identify the dependencies that your component or service needs in order to work properly.
In your component or service class, define a constructor that takes the dependencies as parameters.
Here is an example of how dependency injection works in Angular:
Suppose we have a component called MyComponent that needs to access a service called DataService in order to retrieve some data from a server.
To do this, MyComponent would need to inject DataService as a dependency.
Here is how this might be done:
First, we would define DataService as an @Injectable service:
@Injectable({
providedIn: 'root'
})
export class DataService {
// implementation of the service goes here
}
Next, we would define MyComponent and specify that it requires DataService as a dependency by adding it as a parameter to the constructor:
@Component({
selector: 'app-my-component',
templateUrl: './my-component.component.html',
styleUrls: ['./my-component.component.css']
})
export class MyComponent {
constructor(private dataService: DataService) { }
}
Finally, we would register DataService as a provider in the @NgModule for MyComponent:
@NgModule({
declarations: [
MyComponent
],
imports: [
// other imports go here
],
providers: [DataService],
bootstrap: [MyComponent]
})
export class MyModule { }
Now, MyComponent can use DataService to fetch data from a server by calling methods on the dataService property, which will be automatically injected by the dependency injection framework.
For example:
this.dataService.getData().subscribe((data : DataType) => {
// do something with the data
});
In this way, dependency injection allows MyComponent to access the functionality provided by DataService without having to worry about how DataService is implemented or how it is created.
This makes MyComponent more modular and testable, and helps to make the overall Angular application more maintainable and flexible.
Benefits of using Dependency Injection in Angular
There are several benefits to using dependency injection in Angular, including:
Improved modularity: Dependency injection allows Angular components and services to be more modular, as they are not tied to a specific implementation of their dependencies.
Improved testability: Dependency injection in angular makes it easy to inject mock dependencies into a component or service, allowing it to be tested in isolation.
Improved maintainability: Dependency injection allows developers to easily swap out one implementation of a dependency for another, without having to modify the component or service that uses it.
Improved readability and understandability: Dependency injection makes it clear which dependencies a component or service requires, and how they are used. This makes it easier for other developers to understand the code and to make changes or additions as needed.
Overall, dependency injection in angular is a powerful and useful tool that can help to improve the modularity, testability, maintainability, and readability of Angular applications.
References and Links
Here are more related references and links that discuss the same subject:
- Angular Documentation
- Dependency injection in Angular
- How to use Services in Angular ?
- How to use Providers in Angular ?
- Using Injector , @Injectable & @Inject in Angular
- How to create a singleton service in Angular ?
- Using provideIn root , any & platform in Angular ?
- How to use ViewProviders in Angular ?
- Using @Self , @SkipSelf & Optional Decorators in Angular
- How to use APP_INITIALIZER provider in Angular ?