How to Ensure a Single Instance of an Angular Service Shared Between Library and Application

Discover how to effectively share a single instance of an Angular service between a library component and an application to streamline communication and data exchange.
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Sharing an Angular Service Between a Library Component and an Application

In the world of Angular, libraries and components often need to interact seamlessly to deliver the best user experience. One common requirement is sending data from an application to a library component. However, developers sometimes encounter issues with service instantiation, leading to unexpected behavior. In this post, we'll explore how to address the problem of sharing an Angular service between a library and an application effectively.

The Problem: Multiple Service Instances

When creating an Angular library that includes components, you might face a situation where you need to send data from your application to a component within the library using a shared service. The code snippet below demonstrates the setup:

Service Declaration:

[[See Video to Reveal this Text or Code Snippet]]

Library Component:

[[See Video to Reveal this Text or Code Snippet]]

In this scenario, multiple instances of the LogMonitorService are being created unintentionally when it is injected both in the application component and inside the library component.

Why Multiple Instances Occur

Root Injector: Using providedIn: 'root' creates a service instance in the root injector.

Library Component: Including LogMonitorService within the providers array of the LogMonitorComponent creates another instance.

Application Module: If there's any mention of LogMonitorService in the providers array of the AppModule, a third instance is created.

This results in three separate instances of the service, preventing data exchange between the application and the library component.

The Solution: Remove Service Providers

To resolve the issue of multiple instances of the service, you should remove the LogMonitorService from the providers within both the LogMonitorComponent and the AppModule. By ensuring that there is only a single instance of the service, you enable smooth communication between the library component and the application component.

Steps to Implement the Solution

Remove the Service from Providers in the Library Component:

Update the LogMonitorComponent to no longer include LogMonitorService in providers:

[[See Video to Reveal this Text or Code Snippet]]

Do Not Include the Service in AppModule Providers:

Ensure that your AppModule does not list LogMonitorService in the providers array.

Inject the Service in Components:

In both the library and the application components, simply inject the service as needed. The Angular dependency injection system will use the single instance from the root injector.

After Implementing Changes

By following these simple changes, you should have a single instance of LogMonitorService that will allow you to effectively exchange data between your application and the library component without any conflicts or unexpected behavior.

Conclusion

Sharing data between an Angular application and a library component can be straightforward when the service is correctly configured. By removing duplicate service instances and relying on a single instance provided in the root injector, you streamline communication and maintain a clean architecture.

If you encounter issues while implementing this solution or have further questions, feel free to reach out for assistance! Happy coding!

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