Скачать или смотреть How to Fix the NG0203 Injection Error in Angular When Using AngularFireDatabase

Learn how to resolve the `NG0203: inject() must be called from an injection context` error in Angular when calling an AngularFireDatabase from a constructor.
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Resolving the NG0203 Injection Error in Angular

In the world of Angular development, encountering runtime errors can be frustrating, especially when you don't know the cause of the issue. A frequently encountered error is NG0203: inject() must be called from an injection context such as a constructor. This error can leave developers puzzled, particularly when everything seems to be set up correctly. In this post, we'll explore this error, why it occurs, and how to fix it, particularly regarding the use of AngularFireDatabase in your Angular application.

The Problem

You may find yourself facing the following error:

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

This error typically arises when you're attempting to use Angular's dependency injection features in places where they are not available. In the example below, the error occurs within a class constructor:

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

When you instantiate the AngularFireDatabase service in your constructor, Angular can't resolve the injector context for it, leading to this error.

Understanding the Angular Dependency Injection System

Angular's dependency injection (DI) system enables the framework to efficiently manage service instances and provide them where they are needed. However, there are specific rules about how and where services can be injected:

Injection Context: The injector must be called from a context that Angular recognizes as valid for injectable services, which typically is within component constructors or service constructors.

Module Providers: Services must be provided in a module or component to make them available for injection.

The Solution: Providing AngularFireDatabase

The main issue in this scenario is that the AngularFireDatabase service needs to be registered with Angular's dependency injector. Follow these steps to resolve the error:

1. Update Your App Module

Make sure that you are providing AngularFireDatabase in your module's providers section. Update your app.module.ts file to include it:

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

By including AngularFireDatabase in the providers array, you are correctly registering it with Angular’s DI system.

2. Use It in Your Class

Once you’ve registered the AngularFireDatabase, you can use it in your component like this:

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

Summary

Understanding Angular's dependency injection can be tricky, especially when first using it with external libraries like Firebase. The NG0203 error typically indicates an issue with how a service is provided. By ensuring that AngularFireDatabase is included in your module's providers, you can eliminate this error and continue developing your application with ease.

If you follow the steps outlined above, you should be well on your way to resolving the injection error and properly utilizing AngularFireDatabase in your Angular project.

Happy coding!