Troubleshooting the NullInjectorError in Angular - Service Provider Missing?

I'm facing an issue in my code where I have buttons that should trigger pop-ups displaying details as a list when clicked. However, every time I click the buttons, I encounter the error mentioned below. It seems like I am unable to access the desired property. Can you help me identify what might be wrong with my code and suggest a way to fix it?

TS Code:

@Component({
  selector: 'warehouse-detail-dialog',
  templateUrl: './warehouse-detail-dialog.component.html',
  styleUrls: ['./warehouse-detail-dialog.component.scss']
})
export class WarehouseDetailDialogComponent implements OnInit {

  cell: ICell;
  userRights: IActionRoleMap;

  displayedColumns: string[] = [
    'EntryPackageBarcode',
    'StockIntegrationCode',
    'ProductName',
    'Balance',
];
dataSource: MatTableDataSource<IStockPackageTransaction>;

@ViewChild(MatPaginator, { static: true }) paginator: MatPaginator;
@ViewChild(MatSort, { static: true }) sort: MatSort;


constructor(
      private _terminalService: TerminalService,
      private _router: Router
  ) {

    _terminalService.onCellDetailChanged.subscribe((response: ICell) => {
      this.cell = response;
      
      this.dataSource = new MatTableDataSource(response.StockPackageTransactions);
      this.dataSource.paginator = this.paginator;
      this.dataSource.sort = this.sort;

  });

     
  }

TS for Service:

cellDetail: ICell;
    onCellDetailChanged: BehaviorSubject<any> = new BehaviorSubject([]);
 getCellDetailById(id: string) {
        return new Promise((resolve, reject) => {
            this._http
                .get("Production/GetCellDetailById/" + id)
                .subscribe((response: ICell) => {
                    this.cellDetail = response;
                    this.onCellDetailChanged.next(this.cellDetail);
                    resolve(this.cellDetail);
                }, reject);
        });
    }

Error:

WarehouseDetailDialogComponent_Host.ngfactory.js? [sm]:1 ERROR NullInjectorError: StaticInjectorError(AppModule)[WarehouseDetailDialogComponent -> TerminalService]: 
  StaticInjectorError(Platform: core)[WarehouseDetailDialogComponent -> TerminalService]: 
    NullInjectorError: No provider for TerminalService!
    at NullInjector.get (core.js:778)
    at resolveToken (core.js:2564)
    at tryResolveToken (core.js:2490)
    at StaticInjector.get (core.js:2353)
    at resolveToken (core.js:2564)
    at tryResolveToken (core.js:2490)
    at StaticInjector.get (core.js:2353)
    at resolveNgModuleDep (core.js:26403)
    at NgModuleRef_.get (core.js:27491)
    at resolveNgModuleDep (core.js:26403)

Answer №1

Make sure to include TerminalService in the providers: [] array within the main module file (most likely app.module.ts). The error message is indicating that there is no provider for TerminalService!

Answer №2

One effective solution is to include it in the providers array within the root module, however, utilizing the providedIn pattern is highly recommended for a key reason: tree-shaking. By providing your services using

@Injectable({
  providedIn: 'root'
})

if they are not used, they will be removed during the tree-shaking process, resulting in a smaller bundle size.

Reference: https://angular.io/guide/providers#providedin-and-ngmodules

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