Executing a function in the constructor of an Angular4 component

Question

Executing a function in the constructor of an Angular4 component

I am currently facing an issue where I am attempting to invoke a modal function within the constructor in Angular 4. However, it seems that the function is not being called properly as it gets highlighted. Upon loading the page, no errors are logged and the modal does not appear as expected. While the screen darkens, the text inside the modal does not display.

constructor(public formBuilder: FormBuilder,
            public router: Router,
            public toastr: ToastrService,
            public http: HttpClient,
            public modalService: BsModalService,) {
  if (this.getWardData) {
    this.displayHint();
  }
}

displayHint(template: TemplateRef<any>) {
  this.modalRef = this.modalService.show(template, {class: 'modal-sm'});
}

HTML

<ng-template #template>
  <div class="modal-body text-center">
    <p>Do you want to Continue where you left?</p>
    <button type="button" class="btn btn-default" (click)="confirm()" >Yes</button>
    <button type="button" class="btn btn-primary" (click)="decline()" >No</button>
  </div>
</ng-template>

angular typescript constructor

Answer 1

Answer №1

Here is a code snippet that you can utilize:

constructor(public formBuilder: FormBuilder,
    public router: Router,
    public toastr: ToastrService,
    public http: HttpClient,
    public modalService: BsModalService, ) {
    // if (this.getData) {
    //   this.showHint();
    // }
  }

  ngOnInit() {
    if (this.getData) {
      this.showHint();
    }
  }

  showHint(template: TemplateRef<any>) {
    this.modalRef = this.modalService.show(template, { class: 'modal-sm' });
  }

Answer 2

Here is a code snippet that you can utilize:

constructor(public formBuilder: FormBuilder,
    public router: Router,
    public toastr: ToastrService,
    public http: HttpClient,
    public modalService: BsModalService, ) {
    // if (this.getData) {
    //   this.showHint();
    // }
  }

  ngOnInit() {
    if (this.getData) {
      this.showHint();
    }
  }

  showHint(template: TemplateRef<any>) {
    this.modalRef = this.modalService.show(template, { class: 'modal-sm' });
  }

Answer 3

Answer №2

It appears that there may be an issue with your modal template implementation. While you can initialize your modal, you must ensure to pass the template parameter (TemplateRef) to the displayHint method. In your view, it seems like you have the necessary template but it lacks a reference in the component implementation. You should include the following code snippet in your component (to establish a reference to your modal template for displaying the modal):

@ViewChild('template') private modalTemplate: TemplateRef<any>;

You should remove this.displayHint() from your constructor and instead add ngAfterViewInit within the ngOnInit implementation. Inside the ngAfterViewInit method, make sure to call the displayHint method:

export class YourComponentName implements AfterViewInit {
    @ViewChild('template') private modalTemplate: TemplateRef<any>;

    getWardData = true;

    constructor(public formBuilder: FormBuilder,
                public router: Router,
                public toastr: ToastrService,
                public http: HttpClient,
                public modalService: BsModalService
    ) {}

    ngAfterViewInit() {
        if (this.getWardData) {
            this.displayHint(this.modalTemplate);
        }
    }

    displayHint(template: TemplateRef<any>) {
      this.modalRef = this.modalService.show(template, {class: 'modal-sm'});
    }
}

It is crucial to understand the distinction between the constructor and the ngOnInit/ngAfterViewInit methods of a component in Angular. The Angular bootstrapping process involves two main stages:

Constructing the components tree
Running change detection

The controller method executes during the "Constructing components tree" stage.

(The reference to the modal template is undefined at this point)

Your ngOnInit method runs during the "Running change detection" stage.

(The reference to the modal template is defined here)

The @Input communication mechanism is processed during the subsequent change detection phase, hence input bindings are not accessible in the constructor.

Therefore, running your modal from the constructor is not feasible.

For more information on lifecycle hooks, refer to this link

You can access a live working example here

Answer 4

It appears that there may be an issue with your modal template implementation. While you can initialize your modal, you must ensure to pass the template parameter (TemplateRef) to the displayHint method. In your view, it seems like you have the necessary template but it lacks a reference in the component implementation. You should include the following code snippet in your component (to establish a reference to your modal template for displaying the modal):

@ViewChild('template') private modalTemplate: TemplateRef<any>;

You should remove this.displayHint() from your constructor and instead add ngAfterViewInit within the ngOnInit implementation. Inside the ngAfterViewInit method, make sure to call the displayHint method:

export class YourComponentName implements AfterViewInit {
    @ViewChild('template') private modalTemplate: TemplateRef<any>;

    getWardData = true;

    constructor(public formBuilder: FormBuilder,
                public router: Router,
                public toastr: ToastrService,
                public http: HttpClient,
                public modalService: BsModalService
    ) {}

    ngAfterViewInit() {
        if (this.getWardData) {
            this.displayHint(this.modalTemplate);
        }
    }

    displayHint(template: TemplateRef<any>) {
      this.modalRef = this.modalService.show(template, {class: 'modal-sm'});
    }
}

It is crucial to understand the distinction between the constructor and the ngOnInit/ngAfterViewInit methods of a component in Angular. The Angular bootstrapping process involves two main stages:

Constructing the components tree
Running change detection

The controller method executes during the "Constructing components tree" stage.

(The reference to the modal template is undefined at this point)

Your ngOnInit method runs during the "Running change detection" stage.

(The reference to the modal template is defined here)

The @Input communication mechanism is processed during the subsequent change detection phase, hence input bindings are not accessible in the constructor.

Therefore, running your modal from the constructor is not feasible.

For more information on lifecycle hooks, refer to this link

You can access a live working example here

Executing a function in the constructor of an Angular4 component

Answer №1

Answer №2

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