Provider inside provider in Ionic2/ Angular2 Application

Question

I am having two provider.

1. AppStorage which is responsible for setting and getting values from storage.

   import { Injectable } from '@angular/core';
   import {Http, Headers, RequestOptions} from '@angular/http';
   import {Observable} from 'rxjs/Rx';
   import {Storage} from '@ionic/storage';
   
   @Injectable()
   export class AppStorage {
   
     constructor(public http: Http, private storage:Storage) {
       console.log('Hello Appstorage Provider');
     }
     setValue(key,value){
       var setPromise = new Promise((resolve,reject)=>{this.storage.set(key,value).then((res)=>{
         return resolve(res);
       })
     });
       return setPromise;
     };
     getValue(key){
       var getPromise = new Promise((resolve,reject)=>{this.storage.get(key).then((val)=>{
         return resolve(val);
         });
       });
       return getPromise;
   
     } 
   }
   

2. OauthService which is my api service.

   import {Http, Headers, RequestOptions} from '@angular/http';
   import { Injectable, Inject} from '@angular/core';
   import 'rxjs/add/operator/map';
   import { AppStorage } from '../providers/appstorage';
   
   @Injectable()
       export class OauthService{
       http: Http;
       response :any;
       appStorage: AppStorage;
       static get parameters() {
           return [[Http]];
       }
       constructor(http: Http,@Inject(AppStorage) appStorage: AppStorage){
       this.http = http;
           this.appStorage = appStorage;
           setTimeout(()=>{
               console.log('Hello OauthService Provider'+this.appStorage+"===="+this.http);
           },3000)
        //output - >Hello OauthService Providerundefined====[object Object] 
       }
     }
   

Now i am adding both the injectable to my app.module

import { NgModule, ErrorHandler } from '@angular/core';
import { IonicApp, IonicModule, IonicErrorHandler } from 'ionic-angular';
import { MyApp } from './app.component';
import { LoginPage } from '../pages/login/login';
import { AppStorage } from '../providers/appstorage';
import { Storage } from '@ionic/storage';
import { OauthService } from '../providers/oauthservice';

@NgModule({
  declarations: [
    MyApp,
    LoginPage
  ],
  imports: [
    IonicModule.forRoot(MyApp)
  ],
  bootstrap: [IonicApp],
  entryComponents: [
    MyApp,
    LoginPage
  ],
  providers: [{provide: ErrorHandler, useClass: IonicErrorHandler},OauthService, Storage, AppStorage]
})
export class AppModule {}

But when i am running the app, the appStorage object in constructor of oauthService is coming as undefined. can you please tell me what mistake i am doing, i am just injecting service inside another service.

Answer 1

Your static parameter getter (parameters) in OauthService provider should include all the providers you inject into the constructor. However, you have injected just the Http provider but not AppStorage provider. I have modified the code accordingly below:

import { Http } from '@angular/http';
import { Injectable } from '@angular/core';
import 'rxjs/add/operator/map';
import { AppStorage } from './appstorage';

@Injectable()
export class OauthService {

    response :any;

    static get parameters() {
        return [[Http], [AppStorage]];
    }

    constructor(private http: Http, private appStorage: AppStorage) {

        setTimeout(() => {
            console.log('Hello OauthService: appStorage=' + this.appStorage + ", http=" + this.http);
        }, 3000)
        //output - >Hello OauthService: appStorage=[object Object], http=[object Object]
    }
}