Part 38 – Validation Inheritance Using NgControl & ControlValueAccessor | Angular 14 series

Welcome to the 38th part of our Angular 14 series. In this article, we will be discussing validation inheritance using NgControl and ControlValueAccessor.

What is NgControl and ControlValueAccessor?

NgControl is an interface in Angular that acts as a base class for form control directives. It provides a way to access the directive’s value and validation status. ControlValueAccessor, on the other hand, is an interface that acts as a bridge between Angular forms and native DOM elements. It allows custom form controls to work with Angular’s form directives and form API.

Validation Inheritance

When working with custom form controls in Angular, it’s important to ensure that validation rules are correctly inherited from the base control class. NgControl provides a way to manage validation and error handling for form controls. By implementing the ControlValueAccessor interface, custom form controls can leverage the validation features provided by NgControl.

Implementing Validation Inheritance

To implement validation inheritance using NgControl and ControlValueAccessor, you will need to create a custom form control and ensure that it correctly handles validation and error handling. This involves implementing the methods defined in the ControlValueAccessor interface, such as registerOnChange, registerOnTouched, writeValue, and setDisabledState.

Example

Here’s a simple example of a custom form control that inherits validation using NgControl and ControlValueAccessor:

    
      // CustomFormControlComponent.ts

      import { Component, forwardRef } from '@angular/core';
      import { NG_VALUE_ACCESSOR, ControlValueAccessor, NgControl } from '@angular/forms';

      @Component({
        selector: 'app-custom-form-control',
        template: `
          
        `,
        providers: [
          {
            provide: NG_VALUE_ACCESSOR,
            useExisting: forwardRef(() => CustomFormControlComponent),
            multi: true
          }
        ]
      })
      export class CustomFormControlComponent implements ControlValueAccessor {
        value: string;

        constructor(private ngControl: NgControl) {
          ngControl.valueAccessor = this;
        }

        // Implement ControlValueAccessor methods
        // ...
      }
    
  

In this example, we create a custom form control component that uses NG_VALUE_ACCESSOR to register itself as a value accessor for Angular forms. We also implement the ControlValueAccessor interface to ensure validation features are correctly inherited from NgControl.

Conclusion

In conclusion, validation inheritance using NgControl and ControlValueAccessor is an important aspect of working with custom form controls in Angular. By correctly implementing the ControlValueAccessor interface, custom form controls can seamlessly integrate with Angular’s form directives and leverage the validation features provided by NgControl.