Solving ‘failed Dependency Injection’ In Angular

Solving ‘failed Dependency Injection’ In Angular

Di is a mechanism that makes it easy to inject dependencies in classes or components. The aim is to have a very modular and maintainable codebase.

Executive Summary

Angular dependency Injection is used so that various classes can be developed independently of each other in an app, since they don’t need to know how to generate or consume their dependencies. This dependency resolution is done by an injector, which is capable of resolving a dependency based on a token.

Failed dependency Injection occurs commonly due to a misspelling inside the injection decorator or missed import on the provider. Occasionally it indicates circular dependency issues.

This article covers five ways to solve the issue of “failed dependency Injection”:

1. Incorrect Injection Decorator: This is mostly caused by a typographical error or an incorrect import of the Injection decorator.
2. Missed or Incorrect Import of Provider: This occurs when the provider dependency cannot be found by the injector, which could be caused by an incorrect or missed import of the provider on the corresponding module.
3. Circular Dependency: This happens when a class has a direct or indirect reference to itself.
4. Missing or Incorrect Provider: This happens when there is no provider for the dependency that we are trying to inject, or when there is an incorrect provider which is not providing the correct dependency.
5. Conflicting Services When Using providedIn: When using the providedIn decorator, annotating services via the same token but in multiple modules causes service conflicts.

Solutions

Incorrect Injection Decorator

• Check that the name of the Inject decorator is spelled correctly. It should be @Inject().
• Ensure that the Inject decorator is imported from @angular/core.

Missed or Incorrect Import of Provider

• Verify that the provider is imported in the corresponding module.
• Double check the paths to ensure that the imports are correct.

Circular Dependency

• Refactor the code to avoid circular dependencies.
• Use forwardRef to break the circular dependency.

Missing or Incorrect Provider

• Verify that the provider is defined in the corresponding module.
• Ensure that the provider is of the correct type.
• Inspect other modules to ensure no other providers accidentally hide or interfere with this one for the same token.

Conflicting Services When Using providedIn

• When using providedIn to register services, annotating the service using the same token in different modules will cause conflicts.
• Ensure that each service is registered using a unique token or refactor the code to avoid the circular dependency.

Conclusion

Failed dependency Injection in Angular is a common issue that can be solved easily by following the above-mentioned solutions. First check the injection decorator syntax, verify the provider imports, debug to avoid circular dependencies and verify there is one provider properly registered for each token. Debugging the errors and understanding the structure of the project might also be needed.

Keyword Phrase Tags

• Angular Dependency Injection
• Failed Dependency Injection
• Missing Provider
• Circular Dependency
• Injection Decorator