7f65089de8
This commit updates the `inject` function docs by: - rephrasing a description to include more usage cases - adding usage examples - making a function itself a public API (vs its alias const that was used previously) PR Close #46168
1.7 KiB
@name inject() must be called from an injection context
@category runtime
@shortDescription inject() must be called from an injection context (a constructor, a factory function or a field initializer)
@description
You see this error when you try to use the inject() function outside of the allowed injection context. The injection context is available during the class creation and initialization.
In practice the inject() calls are allowed in a constructor, a constructor parameter and a field initializer:
@Injectable({providedIn: 'root'})
export class Car {
radio: Radio|undefined;
// OK: field initializer
spareTyre = inject(Tyre);
constructor() {
// OK: constructor body
this.radio = inject(Radio);
}
}
It is also legal to call inject from a provider's factory:
providers: [
{provide: Car, useFactory: () => {
// OK: a class factory
const engine = inject(Engine);
return new Car(engine);
}}
]
Calls to the inject() function outside of the class creation context will result in error. Most notably, calls to inject() are disallowed after a class instance was created, in methods (including lifecycle hooks):
@Component({ ... })
export class CarComponent {
ngOnInit() {
// ERROR: too late, the component instance was already created
const engine = inject(Engine);
engine.start();
}
}
@debugging
Work backwards from the stack trace of the error to identify a place where the disallowed call to inject() is located.
To fix the error move the inject() call to an allowed place (usually a class constructor or a field initializer).
@reviewed 2022-05-27