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How to connect custom components to the Angular Reactive Forms API?

Integrating custom components into complex formulations, such as Angular Reactive Forms, is a common challenge for any development team. Many times, developers use only native HTML components or elements from external libraries like Angular Material, but today you will learn how to create and connect your own components to the Angular Reactive Forms API. This will open doors for you to create more personalized and efficient user experiences.

How to create a custom component?

First, generate a new component in your shared module:

ng generate component Stepper

This component will be automatically added to your shared module, which centralizes the components used throughout the application. Be sure to export the new component so that it is available in other modules.

How to add basic functionality to the Stepper component?

Now let's code the basic Stepper logic. The Stepper component will have two buttons to increment and decrement a value displayed on the screen.

The basic HTML code would look something like this:

<div> <button type="button" (click)="subtract()">-</button>  <div>{{ currentValue }}</div> <button type="button" (click)="add()">+</button></div></div>.

And in TypeScript, the increment logic will be handled:

export class StepperComponent { currentValue = 5;
 add() { this.currentValue++; }
 subtract() { this.currentValue--; } }}

How to integrate Stepper with Angular reactive forms?

For this custom component to work with Reactive Forms, we must implement the ControlValueAccessor interface. This allows Angular to handle the interaction between the forms and the component. Here's how to do it:

1. Implement the interface in your component:

import { Component, forwardRef } from '@angular/core';import { ControlValueAccessor, NG_VALUE_ACCESSOR } from '@angular/forms';
@Component({ selector: 'app-stepper', providers: [{ provide: NG_VALUE_ACCESSOR, useExisting: forwardRef(() => StepperComponent), multi: true }]})export class StepperComponent implements ControlValueAccessor { currentValue = 0;
 writeValue(value: any): void { if (value !== undefined) { this.currentValue = value; } } }
 registerOnChange(fn: any): void { this.onChange = fn; } }
 registerOnTouched(fn: any): void { this.onTouched = fn; }. ..} }

2. Sets the default functions for registering actions and checks:

onChange = (_: any) => {};onTouched = () => {};

3. Updates the add and subtract methods to notify changes.

add() { this.currentValue++; this.onChange(this.currentValue);}
subtract() { this.currentValue--; this.onChange(this.currentValue);}

How to incorporate Stepper into an Angular form.

Finally, add the Stepper component to your form using formControlName. Initialize the value as you wish in FormBuilder:

this.form = this.fb.group({ stock: [100, Validators.required]});

And in the HTML template:

<form [formGroup]="form"> <app-stepper formControlName="stock"></app-stepper></form>.

Practical considerations and tips.

• Seamless integration: When integrating this custom component, make sure it behaves intuitively with other elements.
• Flexibility: In addition to Reactive Forms, this component will also support Template-driven Forms automatically.
• Extensibility: Consider creating new components for other specific needs of your application.

This process allows you to develop highly customizable and effective UI components, which is vital for creating scalable and engaging applications. Now you have the power to build a truly custom UI, taking full advantage of Angular's capabilities. Ready for the next challenge in your development career? Keep exploring and creating!