Div id is null when using ngAfterViewInit

Question

In my application I am using angular, and I am trying to access a div right after the page loads. I have imported Afterviewinit like so:

import { Component, OnInit, ViewChild, AfterViewInit, ElementRef } from '@angular/core';

created a variable:

  @ViewChild('editPreamblesInput') editPreamblesInput: ElementRef;

and then implemented ngAfterViewInit like so:

  ngAfterViewInit(){
    const result = this.editPreamblesInput.nativeElement;
    console.log(result);
  }

my html is like:

  <div id="editPreamblesInput" #editPreamblesInput (mouseenter)="userEditable && isUrl? displayPreamblesLink.show() : null" (mouseleave)="displayPreamblesLink.hide()">
    <input-validation>
      <igx-input-group>
        <input igxInput name="preamblesRef" id="preamblesRef" type="text" formControlName="preamblesRef" [readonly]="!userEditable"
        inputValidationDirective [control]="libraryForm.controls['preamblesRef']"/>
        <label igxLabel for="preamblesRef">Preambles Reference</label>
      </igx-input-group>
    </input-validation>

  <igx-action-strip #displayPreamblesLink [displayDensity]="displayDensity" class="action-strip" [hidden]="true">
      <igx-buttongroup [multiSelection]="true" class="buttons">
          <button igxButton type="button" (click)="editPreamblesRef()">
              <igx-icon>link</igx-icon>
          </button>
      </igx-buttongroup>
  </igx-action-strip>
  </div>

However, when I look at my console I get the error: ERROR TypeError: Cannot read properties of undefined (reading 'nativeElement') at LibrarySetupComponent.ng

and editPreamnlesInput is null.

I'm not sure why this is null and what I am missing?

Edit:

So I've figured out why this is happening. The div is a part of a form which only shows if a boolean called loaded is set to true:

this gets set to true in a method called getData():

  getData() {
    this.libraryService.getAll().subscribe({
      next: (libraries) => {
        this.libraryList = libraries;

        if(this.route.snapshot.params['libraryId']) {
          const library = this.libraryList.find(l => l.id == this.route.snapshot.params['libraryId']);
          this.patchLibrary(library);
        } else {
          this.patchLibrary(this.getNewLibrary());
        }
        this.loaded = true;
      },
      error: (err) => {
        this.alertService.error(`Error getting ${this.alertVariable} data - ${err.message}`);
      }
    });
  }

this is then called in the ngOnInit method. loaded has a default value of false, if I change this to true I can then access that element. So I thought I could do something like:

  complete:() => {
    const test = document.getElementById("editPreamblesInput");
    console.log(test);

however test comes up as null. So I'm thinking I need to find a way so that I tell it to wait until the boolean is true before it tries to access it but not sure how

Answer 1

You need to use a template variable to access it.

Inside your template:

<div #div>Hello, world!</div>

Inside your component:

@Component({ ...})
export class MyComponent implements AfterViewInit {
  @ViewChild('div') div?: ElementRef;

  ngAfterViewInit(): void {
    if (this.div) {
      console.log(this.div);
    }
  }
}

Here's a StackBlitz to see it in action:

https://stackblitz.com/edit/angular-l1qyro?file=src%2Fmain.ts

Answer 2

editPreamblesInput element is available when ngAfterViewInit is called, you can wrap your code in a setTimeout function with a minimal delay. like

ngAfterViewInit() {
  setTimeout(() => {
    const result = this.editPreamblesInput.nativeElement;
    console.log(result);
  }, 0);
}

Additionally

@ViewChild('editPreamblesInput', { static: false }) editPreamblesInput: ElementRef;

{ static: false } option is used when the queried element is inside a structural directive such as *ngIf or *ngFor. This ensures that the element is resolved dynamically during runtime.

hope it's work

Answer 3

This is not the best code but it will work:

ngAfterViewInit() {
    const interval = setInterval(() => {
        const result = this.editPreamblesInput.nativeElement;
        if (result != null) {
            console.log(result);
            clearInterval(interval);
        }
    }, 100)
}

This code will keep executing every 100ms until result is not null and not undefined! Not the best code because there's a performance cost to keep executing code but given that the code inside setInterval is fairly lightweight you should be OK.