Angular 4 Subscribe method call multiple times

user_4014086 0
Viewed 31664

im creating a global modal component. My problem is when i call the subscribe method it call multiple times base on the number of the modal was called. How can i prevent mutiple calls on observable subscribe method? Please check my code below. Thanks in advance.

modal.model.ts

export class Modal {
  title: string;
  message: string;
  visible: boolean = false;
}

modal.service

import { Injectable } from '@angular/core';
import { Modal } from './modal.model';
import { Observable } from 'rxjs';
import { Subject } from 'rxjs/Subject';

@Injectable()
export class ModalService {
  static readonly YES = 1;
  static readonly NO = 0;

  private modal = new Modal();
  private subject = new Subject<Modal>();
  private action = new Subject<number>();

  confirmationDialog(message) {
    this.modal.title = 'Confirmation';
    this.modal.message = message;
    return this;
  }

  show() {
    this.modal.visible = true;
    this.setModal(this.modal);
    return this;
  }

  setAction(action: number) {
    this.action.next(<number>action);
  }

  getAction(): Observable<any> {
    return this.action.asObservable();
  }

  setModal(alert: Modal) {
    this.subject.next(<Modal>alert);
    return this;
  }

  getModal(): Observable<any> {
    return this.subject.asObservable();
  }
}

modal.component

import { Component, OnInit } from '@angular/core';
import { ModalService } from './modal.service';
import { Modal } from './modal.model';

@Component({
  selector: 'modal',
  templateUrl: './modal.component.html',
  styleUrls: ['./modal.component.css']
})
export class ModalComponent implements OnInit {
  public modal: Modal;

  constructor(private modalService: ModalService){}

  ngOnInit() {
    this.modalService.getModal().subscribe((modal: Modal) => {
      this.modal = modal;
      console.log(modal);
    });
  }

  no() {
    this.modalService.setAction(0);
    this.modalService.close();
  }

  yes() {
    this.modalService.setAction(1);
    this.modalService.close();
  }
}

calling the modal component

showModal() {
  this.modalService.confirmationDialog('Are you sure you want to save this record?').show();
  this.modalService.getAction().subscribe(response => {
    if(response === ModalService.NO) {
      return;
    }
    console.log('call mutiple times');
  });
}

Here is the screenshot of the output on the console log. console log output

typescript2.0 rxjs angular
3 Answers

Just don't forget to unsubscribe modalService when your component is destroyed.. eg.

...
export class ModalComponent implements OnInit, OnDestroy {
  public modal: Modal;

  constructor(private modalService: ModalService){}

  public ngOnDestroy(): void {
    this.modalService.unsubscribe(); // or something similar
  }
}

What's could be happened is that every time you open the modal the subscription keeps persisted and will be executed +1 time, but using destroy when the modal is closed or destroyed, you'll be removing the subscription as well.

Or even better, basically every time you subscribe you're creating a new observable, but you could reuse the first one you create, applying a simple validation (heads up, you shouldn't use unsubscribe in this case). eg.

if (this.modalService.getModal().observers.length === 0) {
    this.modalService.getModal().subscribe((modal: Modal) => {
        this.modal = modal;
        console.log(modal);
    });
}

There's many ways to prevent triggered subscribers more than once.

user_56620600
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