I'm about to use a multi-provider to export the dependencies of my dependency along with itself, so they could be injected into a ponent at once.

For a ponent

import {Component} from 'angular2/core';
import { FOO_PROVIDERS } from './foo';

@Component({
  selector: 'app',
  providers: [FOO_PROVIDERS]
})
export class App {}

the following

import {Inject, Injectable, provide} from 'angular2/core';
import {Http, HTTP_PROVIDERS} from 'angular2/http';

export class Foo {
  constructor(@Inject(Http) http) {}
}

export const FOO_PROVIDERS = [
  provide(Foo, { useClass: Foo, multi: true }),
  provide(Foo, { useValue: HTTP_PROVIDERS, multi: true })
];

will result in

No provider for Http! (App -> Foo -> Http)

And this

import {Inject, provide} from 'angular2/core';
import {Http, HTTP_PROVIDERS} from 'angular2/http';

class Foo {
  constructor(@Inject(Http) http) {}
}

export const FOO_PROVIDERS = [Foo, HTTP_PROVIDERS];

will work fine, while I would expect them to do the similar job.

Is there a proper use for multi-provider in this case?

I'm about to use a multi-provider to export the dependencies of my dependency along with itself, so they could be injected into a ponent at once.

For a ponent

import {Component} from 'angular2/core';
import { FOO_PROVIDERS } from './foo';

@Component({
  selector: 'app',
  providers: [FOO_PROVIDERS]
})
export class App {}

the following

import {Inject, Injectable, provide} from 'angular2/core';
import {Http, HTTP_PROVIDERS} from 'angular2/http';

export class Foo {
  constructor(@Inject(Http) http) {}
}

export const FOO_PROVIDERS = [
  provide(Foo, { useClass: Foo, multi: true }),
  provide(Foo, { useValue: HTTP_PROVIDERS, multi: true })
];

will result in

No provider for Http! (App -> Foo -> Http)

And this

import {Inject, provide} from 'angular2/core';
import {Http, HTTP_PROVIDERS} from 'angular2/http';

class Foo {
  constructor(@Inject(Http) http) {}
}

export const FOO_PROVIDERS = [Foo, HTTP_PROVIDERS];

will work fine, while I would expect them to do the similar job.

Is there a proper use for multi-provider in this case?

• javascript
• typescript
• angular
• angular2-services

• as a note: one hangup I had- make sure to put FOO_PROVIDERS after defining class FOO, not before – Tucker Commented Mar 9, 2016 at 1:45
• @Tucker That's correct, classes are not hoisted. – Estus Flask Commented Mar 9, 2016 at 8:33
• what is provide here???there is no in angular/core – heliya rb Commented Apr 20, 2022 at 8:04
• @heliyaRahbar It's the definition of a provider. The question addresses Angular 2, provide function was removed in later versions, where provide key is used instead angular.io/guide/… – Estus Flask Commented Apr 20, 2022 at 8:29

1 Answer 1

When you register provide(Foo, ...), than you can

constructor(foo:Foo)

with multi: true you get passed all providers registered as Foo

constructor(foo:any)

With

export const FOO_PROVIDERS = [
  provide(Foo, { useClass: Foo, multi: true }),
  provide(Foo, { useValue: HTTP_PROVIDERS, multi: true })
];

and

constructor(@Inject(Foo) foo:Foo[])

you would get passed to foo an array containing an instance of Foo and a as 2nd item a list of providers (these contained in HTTP_PROVIDERS)

update

Maybe you have different expectations of what should happen. I don't see how @Inject(Http) http is related here. HTTP_PROVIDERS is only registered as value for Foo. What value you pass to useValue is irrelevant when providers are resolved. DI looks up providers for Foo and passed the assigned value and doesn't care at all what that value is. There is no provider for Http in your example therefore Foo itself couldn't get Http injected. You would need to register Http, which is done when you add HTTP_PROVIDERS directly to providers (not in useValue) because HTTP_PROVIDERS contains Http (which is equivalent to provide(Http, {useClass: Http})

update2

// An injected service that itself needs to get passed in a dependency
@Injectable()
class Foo {
  constructor(private http:Http);
}

// container for a bunch of dependencies    
@Injectable()
class MyProviders {
  // add everything you want to make available in your ponents
  constructor(public foo:Foo, public bar:Bar, ...);
}

class MyComponent {
  // inject just MyProviders and use the dependencies it provides
  constructor(private providers: MyProviders) {
    // access provided values
    providers.foo.doSomething();
    providers.bar.doSomethingElse();
  }
}

// Add all providers to allow DI to resolve all above dependencies
bootstrap(AppComponent, [HTTP_PROVIDERS, Foo, Bar]);

}