Angular 7: NullInjectorError: No provider for PagerService

Question

I am trying to implement pagination but It's not working. Here is my code:

pager.service.ts:

  import * as _ from 'underscore';
  @Injectable({
      providedIn: 'root',
  })
export class PagerService {
  getPager(totalItems: number, currentPage: number = 1, pageSize: number = 10) {

    // calculate total pages
    let totalPages = Math.ceil(totalItems / pageSize);

    let startPage: number, endPage: number;
    if (totalPages <= 10) {
      // less than 10 total pages so show all
      startPage = 1;
      endPage = totalPages;
    } else {
      // more than 10 total pages so calculate start and end pages
      if (currentPage <= 6) {
        startPage = 1;
        endPage = 10;
      } else if (currentPage + 4 >= totalPages) {
        startPage = totalPages - 9;
        endPage = totalPages;
      } else {
        startPage = currentPage - 5;
        endPage = currentPage + 4;
      }
    }

    // calculate start and end item indexes
    let startIndex = (currentPage - 1) * pageSize;
    let endIndex = Math.min(startIndex + pageSize - 1, totalItems - 1);

    // create an array of pages to ng-repeat in the pager control
    let pages = _.range(startPage, endPage + 1);

    // return object with all pager properties required by the view
    return {
      totalItems: totalItems,
      currentPage: currentPage,
      pageSize: pageSize,
      totalPages: totalPages,
      startPage: startPage,
      endPage: endPage,
      startIndex: startIndex,
      endIndex: endIndex,
      pages: pages
    };
  }
}

quick-worker-list.component.ts:

import { JobService } from '@app/services';
import { PagerService } from './../../../services/pager.service';
import { Component, OnInit, Input } from '@angular/core';

import * as _ from 'underscore';

@Component({
  selector: 'app-quick-worker-list',
  templateUrl: './quick-worker-list.component.html',
  styles: []
})
export class QuickWorkerListComponent implements OnInit {
  S3ImageUrl: string;

  // array of all items to be paged
  private workerData: any[];

  // pager object
  pager: any = {};

  // paged items
  pagedItems: any[];


  constructor(private pagerService: PagerService, private jobService: JobService) {
  }

  ngOnInit() {
    this.jobService.getQuickJobWorkerList(1301, 1)
      .map((response: Response) => response.json())
      .subscribe(data => {
        // set items to json response
        this.workerData = data;

        // initialize to page 1
        this.setPage(1);
      });
  }

  setPage(page: number) {
    if (page < 1 || page > this.pager.totalPages) {
      return;
    }

    // get pager object from service
    this.pager = this.pagerService.getPager(this.allItems.length, page);

    // get current page of items
    this.pagedItems = this.allItems.slice(this.pager.startIndex, this.pager.endIndex + 1);
  }
}

I get this error:

QuickWorkerListComponent_Host.ngfactory.js? [sm]:1 ERROR Error: StaticInjectorError(AppModule)[QuickWorkerListComponent -> PagerService]: StaticInjectorError(Platform: core)[QuickWorkerListComponent -> PagerService]: NullInjectorError: No provider for PagerService! at NullInjector.push../node_modules/@angular/core/fesm5/core.js.NullInjector.get (core.js:3228) at resolveToken (core.js:3473) at tryResolveToken (core.js:3417) at StaticInjector.push../node_modules/@angular/core/fesm5/core.js.StaticInjector.get (core.js:3314) at resolveToken (core.js:3473) at tryResolveToken (core.js:3417) at StaticInjector.push../node_modules/@angular/core/fesm5/core.js.StaticInjector.get (core.js:3314) at resolveNgModuleDep (core.js:19784) at NgModuleRef_.push../node_modules/@angular/core/fesm5/core.js.NgModuleRef_.get (core.js:20473) at resolveNgModuleDep (core.js:19784)

Answer 1

Following the error text, you have to import and add your PagerService in the Provider part of your app.module.ts file:

providers: [
    PagerService,
  ],

And don't forget to declare it as Injectable:

@Injectable()
export class PagerService {

   // ...

}

Answer 2

Your error is related to PagerService, not with the underscore

NullInjectorError: No provider for PagerService! at

make sure your service is registered in list of providers at app.module or has the Injectable declaration at top:

@Injectable({
  providedIn: 'root',
})

a common example of service in angular 7 is below:

import { Injectable } from '@angular/core';

@Injectable({
  providedIn: 'root',
})
export class MyService{

  constructor() { }

}

please refer to documentation for Services for more details.

Answer 3

Page Service or Job Service both should have Injectable attribute applied or check if you are injecting something in these services also then same applies to that also.