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What makes a component fail to update its template when a Boolean value changes, in the Angular app?

In an Angular 11 app, I have a simle service that mekes a get request and reads a JSON.
The service:
import { Injectable } from '#angular/core';
import { HttpClient } from '#angular/common/http';
import { Promo } from '../models/promo';
#Injectable({
providedIn: 'root'
})
export class PromoService {
public apiURL: string;
constructor(private http: HttpClient) {
this.apiURL = `https://api.url.com/`;
}
public getPromoData(){
return this.http.get<Promo>(`${this.apiURL}/promo`);
}
}
In the the component, I need to compare the array of products with the array of campaign products (included in the JSON mantioned above) and higlight the promoted products:
export class ProductCardComponent extends DestroyableComponent implements OnInit, OnChanges
{
public promoData: any;
public promoProducts: any;
public isPromoProduct: boolean = false;
public ngOnInit() {
this.getCampaignData();
}
public ngOnChanges(changes: SimpleChanges): void {
this.getCampaignData();
}
public getPromoData() {
this.promoService.getPromoData().pipe(takeUntil(this.destroyed$)).subscribe(data => {
this.promoData = data;
this.promoProducts = this.promoData.products;
let promoProduct = this.promoProducts.find((product:any) => {
return this.product.unique_identifier == product.unique_identifier;
});
if (promoProduct) {
// Update boolean
this.isPromoProduct = true;
}
});
}
}
In the component's html file (template), I have:
<span *ngIf="isPromoProduct" class="promo">Promo</span>
There are no compilation errors.
The problem
For a reason I have been unable to understand, the template does not react to the change of the variable isPromoProduct and the template is not updated, despite the fact that I call the function inside ngOnInit and ngOnChanges.
Questions:
Where is my mistake?
What is a reliable way to update the template?

subscribing to Observable inside .ts file it's mostly not a best practice.
try to avoid it by using async pipe of Angular.
you need to store the observable in the variable and not the data returned from the observable, for example:
// this variable holds the `observable` itself.
this.promoData$ = this.promoService.getPromoData()
and then in the template you can do it like this:
<div *ngIf="promoData$ | async as promoData">
here you can access the promoData
</div>
you can still use pipe() to map the data etc but avoid the subscribe()

The isPromoProduct boolean is not an input. The ngOnChanges gets triggered for changes on your properties that are decorated with the #Input decorator. For your particular case, you can inject the ChangeDetectorRef and trigger change detection manually:
constructor(private cdr: ChangeDetectorRef) {}
// ...
public getPromoData() {
this.promoService.getPromoData().subscribe(data => {
// ...
if (promoProduct) {
// Update boolean
this.isPromoProduct = true;
this.cdr.detectChanges();
}
});
}
You also don't need to manage httpClient subscriptions. The observables generated by a simple get or post request will complete after they emit the response of the request. You only need to explicitly manage the unsubscribe for hot observables (that you create from subjects that you instantiate yourself).

Angular call parent component function from child component, update variable in real time from sessionStorage

The code starts with an initial value in product variable, which is setted into sessionStorage. When i trigger the side-panel (child component), this receive the product.name from params in url, then this component searchs in sessionStorage and updates the product.amount value (and set it to sessionStorage).
The parent component function that i'm trying to invoke from the child component is getProductStatus(); When i update the product.amount value in the side-panel i need to update also the product object in parent component at the same time. This is what i've been trying, Thanks in advance.
Code:
https://stackblitz.com/edit/angular-ivy-npo4z7?file=src%2Fapp%2Fapp.component.html
export class AppComponent {
product: any;
productReturned: any;
constructor() {
this.product = {
name: 'foo',
amount: 1
};
}
ngOnInit() {
this.getProductStatus();
}
getProductStatus(): void {
this.productReturned = this.getStorage();
if (this.productReturned) {
this.product = JSON.parse(this.productReturned);
} else {
this.setStorage();
}
}
setStorage(): void {
sessionStorage.setItem(this.product.name, JSON.stringify(this.product));
}
getStorage() {
return sessionStorage.getItem(this.product.name);
}
reset() {
sessionStorage.clear();
window.location.reload();
}
}

You have two options for data sharing in this case. If you only need the data in your parent component:
In child.component.ts:
#Output() someEvent = new EventEmitter
someFunction(): void {
this.someEvent.emit('Some data...')
}
In parent template:
<app-child (someEvent)="handleSomeEvent($event)"></app-child>
In parent.component.ts:
handleSomeEvent(event: any): void {
// Do something (with the event data) or call any functions in the component
}
If you might need the data in another component aswell, you could make a service bound to the root of the application with a Subject to subscibe to in any unrelated component wherever in your application.
Service:
#Injectable()
export class DataService {
private _data = new BehaviorSubject<SnapshotSelection>(new Data());
private dataStore: { data: any }
get data() {
return this.dataStore.asObservable();
}
updatedDataSelection(data: Data){
this.dataStore.data.push(data);
}
}
Just pass the service in both constructors of receiving and outgoing component.
In ngOnInit() on receiving side:
subscription!: Subscription
...
dataService.data.subscribe(data => {
// Do something when data changes
})
...
ngOnDestroy() {
this.subscription.unsubscribe()
}
Then just use updatedDataSelection() where the changes originate.
I documented on all types of data sharing between components here:
https://github.com/H3AR7B3A7/EarlyAngularProjects/tree/master/dataSharing
For an example on the data service:
https://github.com/H3AR7B3A7/EarlyAngularProjects/tree/master/dataService

How to load dynamic components based on a property from object?

I'm trying to build a list of cards which may contain different components; So for example I have the following array of objects:
{
title: 'Title',
descrption: 'Description',
template: 'table',
},
{
title: 'Title',
descrption: 'Description',
template: 'chart',
}
I get this array as a response from a service, then I need to match each of thos objects to a component based on the template property, so for example, the first item should match to the TableComponent and the second one to the ChartComponent;
I'm trying to follow the Angular Docs regarding Dynamic Component Loading, but I'm not sure how tell the method how to match each object in the array to a specific component.
In my parent component I have made an anchor point where the components should load with a directive:
<ng-template appCheckpointHost></ng-template>
And I'm trying to use the ComponentFactoryResolver as it shows in the example.
loadComponent() {
const componentFactory = this.componentFactoryResolver.resolveComponentFactory(ChartCheckpointComponent);
const viewContainerRef = this.checkHost.viewContainerRef;
}
The example shows a scenario in which the "service" runs every three seconds, gets a random item, and shows it; but what I'm trying to do instead is to fetch all the items when the parent component loads, and render each item with its respective component.
Any ideas to get this to work?

You can create a dictionary like:
const nameToComponentMap = {
table: TableComponent,
chart: ChartComponent
};
And then just use this dictionary to determine which component should be rendered depending on the template property of particular item in your items array:
const componentTypeToRender = nameToComponentMap[item.template];
this.componentFactoryResolver.resolveComponentFactory(componentTypeToRender);

You can view my blog here
First I will need to create a directive to reference to our template instance in view
import { Directive, ViewContainerRef } from "#angular/core";
#Directive({
selector: "[dynamic-ref]"
})
export class DynamicDirective {
constructor(public viewContainerRef: ViewContainerRef) {}
}
Then we simply put the directive inside the view like this
<ng-template dynamic-ref></ng-template>
We put the directive dynamic-ref to ng-content so that we can let Angular know where the component will be render
Next I will create a service to generate the component and destroy it
import {
ComponentFactoryResolver,
Injectable,
ComponentRef
} from "#angular/core";
#Injectable()
export class ComponentFactoryService {
private componentRef: ComponentRef<any>;
constructor(private componentFactoryResolver: ComponentFactoryResolver) {}
createComponent(
componentInstance: any,
viewContainer: any
): ComponentRef<any> {
const componentFactory = this.componentFactoryResolver.resolveComponentFactory(
componentInstance
);
const viewContainerRef = viewContainer.viewContainerRef;
viewContainerRef.clear();
this.componentRef = viewContainerRef.createComponent(componentFactory);
return this.componentRef;
}
destroyComponent() {
if (this.componentRef) {
this.componentRef.destroy();
}
}
}
Finally in our component we can call the service like this
#ViewChild(DynamicDirective) dynamic: DynamicDirective;
constructor(
private componentFactoryService: ComponentFactoryService
) {
}
ngOnInit(){
const dynamiCreateComponent = this.componentFactoryService.createComponent(TestComponent, this.dynamic);
(<TestComponent>dynamiCreateComponent.instance).data = 1;
(<TestComponent>dynamiCreateComponent.instance).eventOutput.subscribe(x => console.log(x));
}
ngOnDestroy(){
this.componentFactoryService.destroyComponent();
}
/////////////////////////////////
export class TestComponent {
#Input() data;
#Output() eventOutput: EventEmitter<any> = new EventEmitter<any>();
onBtnClick() {
this.eventOutput.emit("Button is click");
}
}

function variable dynamic setting

This question related to Syntactically anonymous/Arrow Function/add-hoc/factory DP functions:
I have a component which is embedded in the Html.
The component has a click event which is binded to a function. This function content depend on another component which has a reference to this component.
This is the component with the click event:
HTML:
<div (click)="doSomething()">Content.....</div> \\ Should it be with a brackets ?
In the component I just want to define the function signature:
#Component({
selector: 'app-embedded'
})
export class className
{
constructor() { }
ngOnInit() { }
doSomething:(booleanparams: boolean) => any; //The function get a boolean parameter as input and return void or any
}
Now this is where the component is embedded:
<div >
<app-embedded #emb></app-embedded>
</div>
This is the component of the container of the embedded component, which has a reference to the embedded component:
#Component({
selector: 'app-container',
})
export class container
{
#ViewChild('emb') private emb: ElementRef;
booleanParam : booelan;
constructor()
{
emb.doSomething = containerFunction(true);
}
containerFunction(booleanParam : boolean)
{
// do something in this context
}
}
The idea is that this embedded component is embedded in many other containers and whenever the click event triggered a function that was set in the doSomething function variable should be executed.
What changes in the code I need to do in order to accomplish this ?

The best way i see of doing this would be to simply use an event emitter and capture the event on the other side? so embedded would have this:
#Component({
selector: 'app-embedded'
})
export class className
{
#Output()
public something: EventEmitter<boolean> = new EventEmitter<boolean>();
constructor() { }
ngOnInit() { }
doSomething:(booleanparams: boolean) {
this.something.emit(booleanparams);
}; //The function get a boolean parameter as input and return void or any
}
Then where it is called:
<div >
<app-embedded #emb (something)="doSomething($event)"></app-embedded>
</div>
Other solution that would allow a return
#Component({
selector: 'app-embedded'
})
export class className
{
#Input()
public somethingFunc: (boolean)=>any;
constructor() { }
ngOnInit() { }
doSomething:(booleanparams: boolean) {
let w_potato = this.somethingFunc(booleanparams);
//Do whatever you want with w_potato
}; //The function get a boolean parameter as input and return void or any
}
in this case the view would be
<div >
<app-embedded #emb [somethingFunc]="doSomething"></app-embedded>
</div>
I hope this helps! Passing the function or emitting an event will be much more angular than trying to modify an instance of a component. On top of that, a constructor is only called once when Angular starts up so #emb at that time will not be defined to be anything. If you wanted to do it that way you would have to bind yourself in something ngAfterViewInit.
But again, I think that passing it through attributes will be much more angular looking.
Good Luck let me know if this doesn't suit your answer.

Angular; Sharing data between this components

I'm new to Angular and I have this problem here:
I want to pass the data that I have from this service+component to another component.
I have a service doing this:
getRecs() {
let recsSub = new Subject<any>();
let recsSubObservable = from(recsSub);
this.socket.on('recs', (recsStatus: any) => {
recsSub.next(recsStatus);
});
return recsSubObservable;
}
Then I have this parent component
private misRecs = null;
snackBarShown = false;
constructor (private appSocketIoService: AppSocketIoService, private snackbar: MatSnackBar) {
let recsObservable = this.appSocketIoService.getRecommendations();
recsObservable.subscribe((recsStatus: any) => {
console.log(recsStatus);
this.misRecs = {};
for(let property in recsStatus.output){
if (recsStatus.output[property]) {
this.misRecs[property] = recsStatus.output[property];
}
};
this.snackbar.openFromComponent (CustomSnackBar, { duration: 5000, });
});
}
What I need is to populate a list in another component with the values obtained from recsStatus but I don't know how to do it.
Thank you all for your help.

If the component is a child component of your component (parent) you describe in the listing you can use the #Input() annotation.
#Component({
selector: 'child-comp',
template: `
<div>
{{ localRecStatus | json }}
</div>
`
})
export class ChildComponent {
#Input()
localRecStatus: [];
}
Now you can use the component in HTML file of your parent component like this:
<child-comp [localRecStatus]="recStatus"></child-comp>
With this, you can use recStatus in your child component. However, recStatus must be a public variable of the parent component. With this technique, you can pass any data to child components. There is also an #Output() annotation you can use in combination with an EventEmitter to send data to the parent component. If the component is not a child, probably a better way is to communicate via a Service between both components.