Tips for refreshing the service page in Ionic 2

Question

Tips for refreshing the service page in Ionic 2

One of my services is called "user-data", and its main function is to fetch "user data" when a request is received.

I have a specific page that is responsible for displaying this "user data". Upon loading the page, it retrieves the data and displays it.

Additionally, I have a menu with various buttons. Clicking on these buttons triggers a request to the "user-data" service to modify the data. After the data is modified, I want the page to be notified of the change and adjust accordingly.

The approach I take is as follows:

In the service: an event named "user:change" is published along with the updated data

export class UserData{
    users = [];
    ....
    //- if data is changed, 
    //- publish an event
    setUsers(users) {
        this.users = users;
        this.events.publish('user:change', users);
    }
}

In the page, subscribing to listen for this event

export class UserListPage {
    users = [];

    //- subscribe when the page is about to show
    ionViewWillEnter() {
        this.events.subscribe('user:change', this.updateUsers);
    }

    //- unsubscribe when leaving the page
    ionViewDidLeave() {
        this.events.unsubscribe('user:change', this.updateUsers);
    }

    //- update
    updateUsers(userEventData) {

        console.log('About to update');
        if (userEventData[0] instanceof Array) {
             this.users = userEventData[0];
        }
        console.log(this.users);
    }

}

While everything works well within the updateUsers function, the issue arises when trying to assign a new value to this.users. It's quite perplexing.

On occasion, during debugging, an error message pops up saying: "attempted to assign to readonly property."

Any idea what might be causing this?

angular typescript ionic2 ionic3

Answer 1

Answer №1

Instead of relying on traditional events, I recommend utilizing Observables for communication between components. While events can achieve the same outcome, using Observables in conjunction with a service to fetch data offers a more efficient approach. You can explore the code implementation in this live example on Plunker.

The flow of communication would be as follows:

Button / Page ---[calls service]---> Service ---[notifies other page and sends data]---> Page

Within the service, you can create an Observable that allows other components to subscribe and receive notifications once the data is available.

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

@Injectable()
export class UserDataService  { 

  private getDataObserver: any;
  public getData: any;

  constructor() {
    this.getDataObserver = null;
    this.getData = Observable.create(observer => {
        this.getDataObserver = observer;
    });
  }

  public getUserData() {
    // Simulated data to be sent to the page
    let userList = [
      { id: 1, name: 'user01 '},
      { id: 2, name: 'user02 '},
      { id: 3, name: 'user03 '}]

    // Simulating an HTTP request delay
    setTimeout(() => {
      // The next method will notify all subscribers and send the data.
      this.getDataObserver.next(userList);
    }, 1000);
  }
}

The next(...) method notifies all subscribers (in this case, the other component) and provides them with the data.

In the receiving component, simply subscribe to the observable to be informed when the data is ready and interact with the service like so:

import { Component } from "@angular/core";
import { UserDataService } from 'service.ts';

@Component({
  templateUrl:"home.html"
})
export class HomePage {

  users: any[];

  constructor(private service: UserDataService) {
      // Subscribing to the observable to fetch the data once it's ready
        this.service.getData.subscribe((userList) => {
      this.users = userList;
    });
    }

  public getData(){
    this.service.getUserData();
  }
}

Ensure to include the UserDataService in the providers array within the main App component to maintain a singleton service instance throughout the application.

import { Component } from "@angular/core";
import { ionicBootstrap, Platform } from 'ionic-angular/index';
import { HomePage } from './home.ts';
import { UserDataService } from 'service.ts';

@Component({
  template: '<ion-nav [root]="rootPage"></ion-nav>',
  providers: [UserDataService]
})
export class MyApp {
  constructor(private platform: Platform) {
    this.rootPage = HomePage;
  }
}

ionicBootstrap(MyApp);

Answer 2

Instead of relying on traditional events, I recommend utilizing Observables for communication between components. While events can achieve the same outcome, using Observables in conjunction with a service to fetch data offers a more efficient approach. You can explore the code implementation in this live example on Plunker.

The flow of communication would be as follows:

Button / Page ---[calls service]---> Service ---[notifies other page and sends data]---> Page

Within the service, you can create an Observable that allows other components to subscribe and receive notifications once the data is available.

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

@Injectable()
export class UserDataService  { 

  private getDataObserver: any;
  public getData: any;

  constructor() {
    this.getDataObserver = null;
    this.getData = Observable.create(observer => {
        this.getDataObserver = observer;
    });
  }

  public getUserData() {
    // Simulated data to be sent to the page
    let userList = [
      { id: 1, name: 'user01 '},
      { id: 2, name: 'user02 '},
      { id: 3, name: 'user03 '}]

    // Simulating an HTTP request delay
    setTimeout(() => {
      // The next method will notify all subscribers and send the data.
      this.getDataObserver.next(userList);
    }, 1000);
  }
}

The next(...) method notifies all subscribers (in this case, the other component) and provides them with the data.

In the receiving component, simply subscribe to the observable to be informed when the data is ready and interact with the service like so:

import { Component } from "@angular/core";
import { UserDataService } from 'service.ts';

@Component({
  templateUrl:"home.html"
})
export class HomePage {

  users: any[];

  constructor(private service: UserDataService) {
      // Subscribing to the observable to fetch the data once it's ready
        this.service.getData.subscribe((userList) => {
      this.users = userList;
    });
    }

  public getData(){
    this.service.getUserData();
  }
}

Ensure to include the UserDataService in the providers array within the main App component to maintain a singleton service instance throughout the application.

import { Component } from "@angular/core";
import { ionicBootstrap, Platform } from 'ionic-angular/index';
import { HomePage } from './home.ts';
import { UserDataService } from 'service.ts';

@Component({
  template: '<ion-nav [root]="rootPage"></ion-nav>',
  providers: [UserDataService]
})
export class MyApp {
  constructor(private platform: Platform) {
    this.rootPage = HomePage;
  }
}

ionicBootstrap(MyApp);

Answer 3

Answer №2

I realized my mistake was in not organizing the "updateUser" function properly. After making some adjustments, the code below now functions correctly:

<pre>
export class UserListPage {
    users = [];

    //- Adding a subscription to be activated when the page is loaded
    ionViewWillEnter() {
        this.events.subscribe('user:change', (userData) => {
            console.log('Preparing for update');
            if (userData[0] instanceof Array) {
                  this.users = userData[0];
            }
            console.log(this.users);
        });
    }

    //- Unsubscribing when leaving the page
    ionViewDidLeave() {
        this.events.unsubscribe('user:change', ()=> {});
    }

}
</pre>

Answer 4

I realized my mistake was in not organizing the "updateUser" function properly. After making some adjustments, the code below now functions correctly:

<pre>
export class UserListPage {
    users = [];

    //- Adding a subscription to be activated when the page is loaded
    ionViewWillEnter() {
        this.events.subscribe('user:change', (userData) => {
            console.log('Preparing for update');
            if (userData[0] instanceof Array) {
                  this.users = userData[0];
            }
            console.log(this.users);
        });
    }

    //- Unsubscribing when leaving the page
    ionViewDidLeave() {
        this.events.unsubscribe('user:change', ()=> {});
    }

}
</pre>

Tips for refreshing the service page in Ionic 2

Answer №1

Answer №2

Similar questions

Issue encountered in Angular 2 Heroes Tour, Step 7

Unable to connect to the directive even after adding it as an input

The issue arises from a custom Angular directive causing a NullInjectorError:StaticInjectorError in the AppModule when trying to inject MatInput into ElementRef

The functionality of the Protractor right click feature is smooth, however, there seems to be an issue with selecting

"Utilizing Postgresql with TypeORM for filtering many-to-many relationships

Adding a custom button to CkEditor 5 in Angular 12: Step by step tutorial

Best practice for setting up components in Angular 2 using HTML

Building powerful web applications using Angular 2 CLI and Express.js

Struggling with the incorporation of Typescript Augmentation into my customized MUI theme

Showing a div based on the selection of multiple options from a multiselect

Is there a way to trigger validation with a disabled property?

Incorporate a fresh attribute to the JSON data in an Angular API response

Error message encountered in Nativescript app on Android only appears in Release build due to java.lang.Unsatisfied

Enhance your production mode with @ngrx/store-devtools

Setting up Mailgun with TypeScript on Firebase Cloud Functions

Unlimited requests sent to the server while subscribing to an observable on HTTP

Exploring Angular 8: Maintaining component state while navigating between components

What is the best way to pass only the second parameter to a function in TypeScript?

How can I implement a button in Angular Ag Grid to delete a row in a cell render

Converting data received from the server into a typescript type within an Angular Service