Error when trying to inject a service into an angular component "EXCEPTION: Can't resolve all parameters for component", why?

In my case, the reason was the following:

• my injectable service A extended another class B
• B had a constructor which required an argument
• I hadn't defined any constructor in A

As a consequence, when trying to create an object A, the default constructor failed. I have no idea why this wasn't a compile error.

I got it fixed by simply adding a constructor in A, which correctly called B's constructor.

Anuglar import paths are case sensitive.Check if your service paths are correct everywhere you use service and also check the letter cases to be correct and identical everywhere.

Im my case, add "emitDecoratorMetadata" and "esModuleInterop" solved the problem.

https://github.com/thymikee/jest-preset-angular/issues/288

When using barrel imports - consider importing injectables first as a rule of thumb.

It happens when referring an interface as well.

Changing interface for class fixed it, working with and without @Inject.

Sometimes this happens when you declared Angular's inbuilt module(HttpClientModule, HttpErrorResponse etc) in app.module.js. I also faced the same issue but resolved now.

The mistake I did was mention HttpClientModule into Providers instead of Import of angular Module

For me this was because i stopped using the -aot flag whilst trying to make the compile time faster.

 ng serve -aot 

For me, it was because I had an empty line between my @Component decorator and my Component class. This caused the decorator not to get applied to the class.

In my case, I took a dependency on a service that had no dependencies and therefore I did not add a constructor() function to the service class. I added a parameterless constructor to the dependent service class and everything started working.

In my case, that was the TypeScript version that I upgraded to a major version and assignation assertions that I added to some Class properties.

Reverting the changes solved this for me. (details here)

to me stopping the application and issuing ng serve fixed the problem

In my case I missed to call the constructor of the class I inherited from.

Before:

@Component({ ... }) export class ComponentA extends ComponentParent { // ... } 

After:

@Component({ ... }) export class ComponentA extends ComponentParent { constructor(protected route: ActivatedRoute, protected store$: Store<AppState>) { super(route, store$); } // ... } 

In my case fix was replacing relative path with absolute before

import {Service} from './service'; 

after

import {Service} from 'src/app/services/service'; 

Looks like typescript/angular issue

You can try running the following command again:

ng serve --open

In may case the error was caused by upgrading the @angular-devkit/build-angular to ~0.803.*. See https://github.com/angular/angular-cli/issues/15892 for the details.

If you try to inject an interface, this error occurs as well:

Somewhere:

export const MY_SERVICE = new InjectionToken<MyService>('MY_SERVICE'); export interface MyService { // ... } @Injectable() export class MyServiceImpl implements MyService { // ... } 

Incorrect:

 constructor( private myService: MyService ) {} 

Correct:

 constructor( @Inject(MY_SERVICE) private myService: MyService ) {} 

The thing is that elements within a module should use relative imports for elements that are part of the same module; they should never import through the module’s public API barrel (or barrels in general btw).

The problem with that import is that if something that depends on the service is loaded first in the barrel (directly or not), then the DI system will fail since the service has not been declared yet and thus can’t be resolved.

Try changing the import from absolute:

import { UserService } from 'src/app/users/user.service'; 

To Relative:

import { UserService } from '../../users/user.service'; 

I tried almost all the answers given here but none of them helped me.

What worked for me was closing the project in Visual Studio Code, opening the file explorer, entering my project and deleting the dist folder.

Then I did every build to all the libs and then re-ran the project in npm start.