Encountered an error trying to access properties that are undefined while working with Ionic Angular, specifically having trouble reading the 'update

As someone who is new to building ionic angular applications (coming from a PHP background), I am currently facing an issue. I have a page with the following code:

export class LicencesTabPage implements OnInit {

  public licencesData: any[] | void;

  constructor(
    protected licenceService: LicencesService,
    protected authService: AuthenticationService,
    protected modelController: ModalController,
    public conversions: DatetimeConversions,
  ) {
  }

  async ngOnInit() {
    this.getData();
  }

  async openDetailedModel(index) {
    const modal = await this.modelController.create({
      component: LicencesDetailedComponent,
      componentProps: {
        itemDetail: this.licencesData[index]
      }
    });

    modal.onDidDismiss().then((modelData) => {
      this.getData();
      if (modelData !== null) {
      }
    });

    return await modal.present();
  }

  protected async getData() {
    const userUUID = await this.authService.getStoredUuid();
    await this.licenceService.getLicences(userUUID).then(res => {
      this.licencesData = JSON.parse(JSON.stringify(res));
    });
  }
}

Users can access a model component by using the openDetailedModel method. Here is the modal component:

export class LicencesDetailedComponent implements OnInit {

  @Input()
  public itemDetail: any = [];
  protected returnValue: any;
  public editItem = false;
  
  // Other declarations omitted for brevity

}

Users can call the updateLicence() method which updates data within the LicencesCommonFunction class. Here is a simplified version of the LicencesCommonFunction class:

export class LicencesCommonFunction implements OnInit {

  public newItem: any;
  protected licencesService: LicencesService;

  // Constructor and other methods omitted for brevity
  
  /**
   *
   * @param form
   */
  updateLicence(form: NgForm) {
      
      this.licencesService.updateLicence(this.newItem).then(() => {
          this.showToast('Updated');
      });
  }
}

When attempting to call the updateLicence method from within the modal component, I encounter the error "Cannot read properties of undefined (reading 'updateLicence')." However, calling it from a page works without issues, indicating that the LicencesService may not be registered when called from within the modal. Any suggestions on how to resolve this issue?

Answer №1

It seems that the usage of dependency injection is inconsistent in your code. In one part, you are correctly injecting dependencies like licenseService, authService, and modelController. However, in another part, your modal component is trying to create its own instances of dependencies.

This can lead to issues, especially if a service like licensesCommonFunctions does not properly instantiate or inject the required services.

To address this issue, I recommend making your common function injectable by using Angular's dependency injection system. This involves annotating the class with @Injectable() and injecting the necessary service through the constructor.

By understanding how dependency injection works in Angular and following best practices, you can avoid errors caused by manually creating service instances instead of leveraging dependency injection.

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