Accessing DOM Elements with ViewChild in Angular

Angular's ViewChild decorator is a powerful tool for accessing DOM elements, child components, or directives within your component's template. This challenge will guide you through using ViewChild to interact with a native DOM element, specifically an input field, to demonstrate its utility. Mastering ViewChild is crucial for building dynamic and interactive Angular applications.

Problem Description

Your task is to create an Angular component that has an input field in its template. Using the ViewChild decorator, you need to obtain a reference to this input element. Once you have the reference, you should implement a method to programmatically set the focus on this input field when a button is clicked.

Key Requirements:

• Create an Angular component.
• In the component's template, include an <input type="text"> element. Assign a template reference variable (e.g., #myInput) to this input element.
• In the component's TypeScript class, use the @ViewChild decorator to get a reference to the input element. The type for the reference should be ElementRef.
• Implement a method, for instance, focusInput(), that will be called when a button is clicked.
• Inside the focusInput() method, use the obtained ViewChild reference to set the focus on the input element. You'll need to access the native element via .nativeElement.
• In the component's template, include a <button> element that triggers the focusInput() method when clicked.

Expected Behavior:

When the component loads, the input field will be visible. Clicking the button will immediately move the cursor (focus) to the input field.

Edge Cases to Consider:

• Ensure the ViewChild reference is accessed only after the view has been initialized to avoid errors. The AfterViewInit lifecycle hook is the appropriate place for this.

Examples

Example 1: (Conceptual - actual output is visual interaction)

Component Template (app.component.html):

<input #myInput type="text" placeholder="Type here...">
<button (click)="focusInput()">Focus Input</button>

Component Class (app.component.ts):

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

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent implements AfterViewInit {
  @ViewChild('myInput') myInputRef!: ElementRef;

  focusInput() {
    if (this.myInputRef) {
      this.myInputRef.nativeElement.focus();
    }
  }

  ngAfterViewInit() {
    // You can optionally focus on init if needed, but the challenge is button click
    // this.focusInput();
  }
}

Explanation:

The @ViewChild('myInput') decorator in the TypeScript class queries the template for an element with the template reference variable #myInput. This reference is then assigned to the myInputRef property of type ElementRef. The focusInput() method retrieves the native DOM element via this.myInputRef.nativeElement and calls its focus() method. The button's click event is bound to call this method.

Constraints

• You must use the @ViewChild decorator.
• The reference obtained via ViewChild must be of type ElementRef.
• The focus action must be triggered by a button click.
• The code should be written in TypeScript and Angular.

Notes

• Remember to import ViewChild, ElementRef, and AfterViewInit from @angular/core.
• The AfterViewInit lifecycle hook is crucial for ensuring that the DOM element is available when you try to access it via ViewChild.
• Consider how you would handle cases where the element might not be present in the DOM under certain conditions (though for this specific problem, it's always present).