failure to render updated content after modification of variable

Question

failure to render updated content after modification of variable

I am facing an issue with triggering a function in the component:

componentA.ts

    html = 'hey';

      this.onElementSelected(r => this.change());

      public change() {

      console.log(this.html);
      if (this.html === 'hey') {

        this.html = 'oh, hello!';
        console.log(this.html);
      } else {
        this.html = 'hey';
      }
  }

componentA.html

This is the code of the associated template:

<div *ngIf="html">{{html}}</div>

While I can see the html variable change with console.log(), it doesn't reflect the change in the template. How can I update the template without using a button within the template?

I have already tested and confirmed that using a button works, but I need the event of change to be triggered by the component itself.

Any suggestions would be greatly appreciated. Thank you for your help.

angular typescript templates view

Answer 1

Answer №1

Have you implemented the ChangedetectionStrategy.OnPush in your Angular project? This approach disconnects Angular from automatically updating your view, so you need to specify when Angular should refresh the view.

If you have used ChangedetectionStrategy.OnPush, here's how you can manually update your component's view:

First, inject ChangeDetectorRef into your constructor:

import { ChangeDetectorRef } from '@angular/core';

...

constructor(private cd: ChangeDetectorRef) {}

Next, after assigning a new value to 'this.html', make sure to call this.cd.detectChanges() to trigger a re-render of the component:

if (this.html === 'hey') {
        this.html = 'oh, hello!';
        this.cd.detectChanges();
...

Answer 2

Have you implemented the ChangedetectionStrategy.OnPush in your Angular project? This approach disconnects Angular from automatically updating your view, so you need to specify when Angular should refresh the view.

If you have used ChangedetectionStrategy.OnPush, here's how you can manually update your component's view:

First, inject ChangeDetectorRef into your constructor:

import { ChangeDetectorRef } from '@angular/core';

...

constructor(private cd: ChangeDetectorRef) {}

Next, after assigning a new value to 'this.html', make sure to call this.cd.detectChanges() to trigger a re-render of the component:

if (this.html === 'hey') {
        this.html = 'oh, hello!';
        this.cd.detectChanges();
...

Answer 3

Answer №2

One approach is to include the ngZone in your component and perform your updates within its run function like this:

import {NgZone} from '@angular/core';  

class YourClass {

        constructor(private ngZone: NgZone) {
                this.htmlSource = new BehaviorSubject('hey');
               this.html$ = this.htmlSource.asObservable();
          }

     this.onElementSelected(r => this.change());

    public change() {
         console.log(this.htmlSource.value);
    this.ngZone.run(() => {
     if (this.htmlSource.value === 'hey') {
          this.htmlSource.next('oh, hello!');
         console.log(this.htmlSource.value);
     } else {
        this.htmlSource.next('hey');
     }

     });
   }
}

Answer 4

One approach is to include the ngZone in your component and perform your updates within its run function like this:

import {NgZone} from '@angular/core';  

class YourClass {

        constructor(private ngZone: NgZone) {
                this.htmlSource = new BehaviorSubject('hey');
               this.html$ = this.htmlSource.asObservable();
          }

     this.onElementSelected(r => this.change());

    public change() {
         console.log(this.htmlSource.value);
    this.ngZone.run(() => {
     if (this.htmlSource.value === 'hey') {
          this.htmlSource.next('oh, hello!');
         console.log(this.htmlSource.value);
     } else {
        this.htmlSource.next('hey');
     }

     });
   }
}

Answer 5

Answer №3

Consider using an Observable with BehaviorSubject in the following way:

public content$: Observable<string>;
private contentSource: BehaviorSubject<string>();
constructor() {
   this.contentSource = new BehaviorSubject('hey');
   this.content$ = this.contentSource.asObservable();
}
  this.onContentChange(r => this.updateDisplay());

  public updateDisplay() {

  console.log(this.contentSource.value);
  if (this.contentSource.value === 'hey') {

    this.contentSource.next('oh, hello!');
    console.log(this.contentSource.value);
  } else {
    this.contentSource.next('hey');
   }
}

Then in the component.html:

<div *ngIf="content$ | async as content">{{content}}</div>

Answer 6

Consider using an Observable with BehaviorSubject in the following way:

public content$: Observable<string>;
private contentSource: BehaviorSubject<string>();
constructor() {
   this.contentSource = new BehaviorSubject('hey');
   this.content$ = this.contentSource.asObservable();
}
  this.onContentChange(r => this.updateDisplay());

  public updateDisplay() {

  console.log(this.contentSource.value);
  if (this.contentSource.value === 'hey') {

    this.contentSource.next('oh, hello!');
    console.log(this.contentSource.value);
  } else {
    this.contentSource.next('hey');
   }
}

Then in the component.html:

<div *ngIf="content$ | async as content">{{content}}</div>

failure to render updated content after modification of variable

Answer №1

Answer №2

Answer №3

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