Determining changes in an object with Angular 2 and Ionic 2

Question

Determining changes in an object with Angular 2 and Ionic 2

Q) How can I detect changes in an object with multiple properties bound to form fields without adding blur events to each individual field?

I want to avoid cluttering the page with too many event listeners, especially since it's already heavy.

For example:

Object:

let person = {
    name: string,
    email: string,
    phone: string
};

Form:

<input [(ngModel)]="person.name" type="text" />
<input [(ngModel)]="person.email" type="text" />
<input [(ngModel)]="person.phone" type="text" />

angular typescript ionic-framework ionic2 ionic3

Answer 1

Answer №1

However, I am in search of an alternative method - akin to the functionality of angular 1's $watch feature. This is crucial because my complex object can undergo changes through various means, not restricted to just basic input fields.

Recently, while working on a Google Autocomplete Component, I encountered a similar dilemma: Upon selecting an address from the Google suggestions after typing, it was necessary to update additional fields such as city, province, and zip code.

Following advice from @Günter Zöchbauer, I implemented an observable to monitor changes within my autocomplete component. However, a challenge arose when the view failed to reflect these updates, attributed to the concept of Zones. For novice users, detailed explanations about Zones can be found here and here.

The aforementioned sources articulate that:

Application state change occurs due to three primary factors:

Events - User interactions like click, change, input, submit, etc.

XMLHttpRequests - Fetching data from external services

Timers - Usage of methods like setTimeout(), setInterval()

Interestingly, Angular solely focuses on updating the view during these scenarios.

Hence, if

there are alternate methods for modifying my intricate object

It becomes imperative to notify Angular regarding any alterations for synchronization with the updated elements. Here's how I accomplished this:

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

@Injectable()
export class AutocompleteService {

    private autocompleteObserver: any;
    public autocomplete: any;

    constructor(...) {
        this.autocompleteObserver = null;

        this.autocomplete = Observable.create(observer => {
            this.autocompleteObserver = observer;
        });
    }

    public initializeAutocomplete(element): void { 

        // Core operations here
        // ...

        // Propagate information to the caller
        this.autocompleteObserver.next(addressInformation);
    }

Subsequently, in my page's .ts file:

import { Component, NgZone } from '@angular/core';
import { AutocompleteService } from '../../providers/autocomplete-service/autocomplete-service';

@Component({
  templateUrl: 'build/pages/my-new-page/my-new-page.html',
  directives: [FORM_DIRECTIVES],
  providers: [AutocompleteService]
})
export class MyNewPage {

    constructor(..., private autocompleteService : AutocompleteService) {
    
        // Initialization steps
        // ... 

       this.autocompleteService.autocomplete.subscribe((addressInfo) => {
           this.ngZone.run(() => {
                // Update the form fields, allowing Angular to handle view updates
                this.updateAddress(addressInfo);
            });
        });
    }
}

By executing certain actions within an angular zone, you effectively signal Angular to acknowledge potential updates requiring reflection within the application.

Answer 2

However, I am in search of an alternative method - akin to the functionality of angular 1's $watch feature. This is crucial because my complex object can undergo changes through various means, not restricted to just basic input fields.

Recently, while working on a Google Autocomplete Component, I encountered a similar dilemma: Upon selecting an address from the Google suggestions after typing, it was necessary to update additional fields such as city, province, and zip code.

Following advice from @Günter Zöchbauer, I implemented an observable to monitor changes within my autocomplete component. However, a challenge arose when the view failed to reflect these updates, attributed to the concept of Zones. For novice users, detailed explanations about Zones can be found here and here.

The aforementioned sources articulate that:

Application state change occurs due to three primary factors:

Events - User interactions like click, change, input, submit, etc.

XMLHttpRequests - Fetching data from external services

Timers - Usage of methods like setTimeout(), setInterval()

Interestingly, Angular solely focuses on updating the view during these scenarios.

Hence, if

there are alternate methods for modifying my intricate object

It becomes imperative to notify Angular regarding any alterations for synchronization with the updated elements. Here's how I accomplished this:

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

@Injectable()
export class AutocompleteService {

    private autocompleteObserver: any;
    public autocomplete: any;

    constructor(...) {
        this.autocompleteObserver = null;

        this.autocomplete = Observable.create(observer => {
            this.autocompleteObserver = observer;
        });
    }

    public initializeAutocomplete(element): void { 

        // Core operations here
        // ...

        // Propagate information to the caller
        this.autocompleteObserver.next(addressInformation);
    }

Subsequently, in my page's .ts file:

import { Component, NgZone } from '@angular/core';
import { AutocompleteService } from '../../providers/autocomplete-service/autocomplete-service';

@Component({
  templateUrl: 'build/pages/my-new-page/my-new-page.html',
  directives: [FORM_DIRECTIVES],
  providers: [AutocompleteService]
})
export class MyNewPage {

    constructor(..., private autocompleteService : AutocompleteService) {
    
        // Initialization steps
        // ... 

       this.autocompleteService.autocomplete.subscribe((addressInfo) => {
           this.ngZone.run(() => {
                // Update the form fields, allowing Angular to handle view updates
                this.updateAddress(addressInfo);
            });
        });
    }
}

By executing certain actions within an angular zone, you effectively signal Angular to acknowledge potential updates requiring reflection within the application.

Answer 3

Answer №2

To determine if a form has been modified, consider using a form object to track its changes.

Although there have been reported challenges with the most recent versions of Angular2 and Ionic2 concerning the new Forms module, utilizing a form object is still recommended.

Visit this link for more information on Angular forms.

Answer 4

To determine if a form has been modified, consider using a form object to track its changes.

Although there have been reported challenges with the most recent versions of Angular2 and Ionic2 concerning the new Forms module, utilizing a form object is still recommended.

Visit this link for more information on Angular forms.

Determining changes in an object with Angular 2 and Ionic 2

Answer №1

Answer №2

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