What is the best way to provide constructor arguments in Ionic 2 / Angular 2?

Question

What is the best way to provide constructor arguments in Ionic 2 / Angular 2?

Currently in the process of upgrading my Ionic2.beta11 App to the latest release, Ionic2.rc0. Most aspects have been relatively smooth sailing, but I've hit a roadblock with the AoT compiler.

Specifically, I'm encountering an issue with my AuthService:

@Injectable()
export class AuthService {
  constructor(@Inject(Http) http: Http) {
    this.http = http;
  }
  ...
}

Within my app, I'm injecting the AuthService into the src/app/app.module.ts file:

@NgModule({
  declarations: [
    MyApp,
    ...
  ],
  imports: [
    IonicModule.forRoot(MyApp)
  ],
  bootstrap: [IonicApp],
  entryComponents: [
    MyApp,
    ...
  ],
  providers: [
    AuthService
  ]
})

While everything functions correctly during ionic serve, complications arise when attempting to build, resulting in the following error message:

ngc error: Error: Error at .../.tmp/app/app.module.ngfactory.ts:397:78: Supplied parameters do not match any signature of call target.

Lines 396 - 399:

get _AuthService_74():import44.AuthService {
  if ((this.__AuthService_74 == (null as any))) { (this.__AuthService_74 = new import44.AuthService()); }
  return this.__AuthService_74;
}

The crux of the issue lies in new import44.AuthService() expecting a parameter of type http.

Interestingly, making a manual adjustment in the definition file from constructor(http: Http) to constructor() resolves the problem.

Despite scouring through various StackOverflow responses, none of the proposed solutions have remedied my situation.

Should I modify the constructor in the AuthService or alter how it's injected into my app? Any assistance would be greatly appreciated.

angular typescript dependency-injection ionic2

Answer 1

Answer №1

To redefine the provider, you need to change your approach:

@NgModule({
  ...
  providers: [
    Http,
    {
      provide: AuthService,
      useFactory: createAuthServiceInstance,
      deps: [Http]
    }
  ]
})

The crucial step is implementing the factory function:

export function createAuthServiceInstance(http: Http): LoggingService {
  return new AuthService(http);
}

For more information, check out Successful Migration to Ionic 3 with ngc

Answer 2

To redefine the provider, you need to change your approach:

@NgModule({
  ...
  providers: [
    Http,
    {
      provide: AuthService,
      useFactory: createAuthServiceInstance,
      deps: [Http]
    }
  ]
})

The crucial step is implementing the factory function:

export function createAuthServiceInstance(http: Http): LoggingService {
  return new AuthService(http);
}

For more information, check out Successful Migration to Ionic 3 with ngc

Answer 3

Answer №2

I encountered a similar issue and thanks to Markus, I was able to find the right solution. Here is what worked for me to resolve the issue (also refer to "Factory Providers" in the Angular docs on Dependency Injection):

Firstly, make sure to mark the constructor parameter in the injected service as optional. However, this alone may not be sufficient as 'http' could still be undefined at runtime.

constructor(public http?: Http){}

Create a new service provider class named SomeServiceProvider.ts:

import { Http } from '@angular/http';
import { SomeService } from 'some-service';

export function someServiceFactory(http: Http){
  return new SomeService(http);
}

export let SomeServiceProvider =
  { provide: SomeService,
    useFactory: someServiceFactory,
    deps: [ Http ]
  };

In the root app.component.ts file, include the newly created service provider:

@Component({
  ...
  providers: [ SomeServiceProvider ]
})

Remember to remove the service from the @NgModule providers in the app.module.ts file.

To access the service in components, retrieve it using the Injector instead of injecting it directly into the component:

import { Component, Injector } from '@angular/core';
import { SomeService } from 'some-service';

@Component({
  ...
})

export class MyComponent{
  someService: SomeService = this.injector.get(SomeService);

  constructor(private injector: Injector) {}

}

Answer 4

I encountered a similar issue and thanks to Markus, I was able to find the right solution. Here is what worked for me to resolve the issue (also refer to "Factory Providers" in the Angular docs on Dependency Injection):

Firstly, make sure to mark the constructor parameter in the injected service as optional. However, this alone may not be sufficient as 'http' could still be undefined at runtime.

constructor(public http?: Http){}

Create a new service provider class named SomeServiceProvider.ts:

import { Http } from '@angular/http';
import { SomeService } from 'some-service';

export function someServiceFactory(http: Http){
  return new SomeService(http);
}

export let SomeServiceProvider =
  { provide: SomeService,
    useFactory: someServiceFactory,
    deps: [ Http ]
  };

In the root app.component.ts file, include the newly created service provider:

@Component({
  ...
  providers: [ SomeServiceProvider ]
})

Remember to remove the service from the @NgModule providers in the app.module.ts file.

To access the service in components, retrieve it using the Injector instead of injecting it directly into the component:

import { Component, Injector } from '@angular/core';
import { SomeService } from 'some-service';

@Component({
  ...
})

export class MyComponent{
  someService: SomeService = this.injector.get(SomeService);

  constructor(private injector: Injector) {}

}

Answer 5

Answer №3

Include HttpModule from @angular/http into your application module like this:

import { HttpModule } from '@angular/http';
@NgModule({
  declarations: [
    MyApp,
    ...
  ],
   imports: [
     HttpModule,
     IonicModule.forRoot(MyApp)
   ],
   bootstrap: [IonicApp],
   entryComponents: [
     MyApp,
     ...
   ],
   providers: [
     AuthService
   ]
})

Update your service code as follows and then test it out:

import { Http } from '@angular/http';
@Injectable()
export class AuthService {
  constructor(private http: Http) {
  }
  ...
}

Answer 6

Include HttpModule from @angular/http into your application module like this:

import { HttpModule } from '@angular/http';
@NgModule({
  declarations: [
    MyApp,
    ...
  ],
   imports: [
     HttpModule,
     IonicModule.forRoot(MyApp)
   ],
   bootstrap: [IonicApp],
   entryComponents: [
     MyApp,
     ...
   ],
   providers: [
     AuthService
   ]
})

Update your service code as follows and then test it out:

import { Http } from '@angular/http';
@Injectable()
export class AuthService {
  constructor(private http: Http) {
  }
  ...
}

What is the best way to provide constructor arguments in Ionic 2 / Angular 2?

Answer №1

Answer №2

Answer №3

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