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What is the role of NG_VALUE_ACCESSOR in a custom component?

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01

Understand the problem

Explain the NG_VALUE_ACCESSOR provider token.

formsdi
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03

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NG_VALUE_ACCESSOR is an InjectionToken used to register custom form controls. By providing it with useExisting: forwardRef(() => MyComponent) and multi: true, the control registers into Angular's Forms registry to communicate state with formControlName.

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04

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Registering NG_VALUE_ACCESSOR inside component metadata
import { Component, forwardRef } from '@angular/core';
import { NG_VALUE_ACCESSOR } from '@angular/forms';

@Component({
  selector: 'app-custom-input',
  providers: [
    {
      provide: NG_VALUE_ACCESSOR,
      useExisting: forwardRef(() => CustomInputComponent),
      multi: true
    }
  ],
  template: '<input (input)="onInput($event)" />'
})
export class CustomInputComponent {
  onInput(event: Event) {
    // notify forms engine...
  }
}
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