angular - ControlValueAccessor with multiple formControl in child component

Angular - ControlValueAccessor with multiple formControl in child component

Implementing ControlValueAccessor with multiple FormControls in a child component allows you to create custom Angular form controls that can be used within Angular's reactive forms. This approach is useful when you need to encapsulate complex UI components or logic into reusable form controls.

Overview

To implement ControlValueAccessor with multiple FormControls in a child component, you need to:

  1. Create a custom component that implements ControlValueAccessor.
  2. Manage the interaction between your custom component and Angular's reactive forms.
  3. Handle the communication between your custom component and the parent form.

Example Implementation

Let's create an example where we have a custom component CustomFormComponent that contains two FormControls: one for a text input and one for a checkbox. This component will implement ControlValueAccessor to allow seamless integration with Angular forms.

Step-by-Step Implementation

  1. Define the Custom Component

Create custom-form.component.ts:

import { Component, forwardRef, OnInit } from '@angular/core'; import { ControlValueAccessor, NG_VALUE_ACCESSOR, FormGroup, FormBuilder } from '@angular/forms'; @Component({ selector: 'app-custom-form', templateUrl: './custom-form.component.html', styleUrls: ['./custom-form.component.css'], providers: [ { provide: NG_VALUE_ACCESSOR, useExisting: forwardRef(() => CustomFormComponent), multi: true } ] }) export class CustomFormComponent implements ControlValueAccessor, OnInit { form: FormGroup; onChange: any = () => {}; onTouch: any = () => {}; constructor(private fb: FormBuilder) { } ngOnInit() { this.form = this.fb.group({ textInput: '', checkboxInput: false }); this.form.valueChanges.subscribe(() => { this.onChange(this.form.value); this.onTouch(); }); } writeValue(value: any) { if (value) { this.form.setValue(value, { emitEvent: false }); } } registerOnChange(fn: any) { this.onChange = fn; } registerOnTouched(fn: any) { this.onTouch = fn; } setDisabledState?(isDisabled: boolean): void { if (isDisabled) { this.form.disable(); } else { this.form.enable(); } } }
  1. Create the Template for the Custom Component

Create custom-form.component.html:

<form [formGroup]="form"> <input type="text" formControlName="textInput" placeholder="Enter text"> <label> <input type="checkbox" formControlName="checkboxInput"> Checkbox </label> </form>
  1. Use the Custom Component in a Parent Component

In the parent component's template (app.component.html), use CustomFormComponent within an Angular form:

<form [formGroup]="parentForm"> <app-custom-form formControlName="customControl"></app-custom-form> </form>
  1. Include the Custom Component in Module

Make sure to include CustomFormComponent in your module (app.module.ts) declarations:

import { NgModule } from '@angular/core'; import { BrowserModule } from '@angular/platform-browser'; import { ReactiveFormsModule } from '@angular/forms'; import { AppComponent } from './app.component'; import { CustomFormComponent } from './custom-form/custom-form.component'; @NgModule({ imports: [BrowserModule, ReactiveFormsModule], declarations: [AppComponent, CustomFormComponent], bootstrap: [AppComponent] }) export class AppModule {}

Explanation

  • ControlValueAccessor Implementation: The CustomFormComponent implements ControlValueAccessor, providing methods (writeValue, registerOnChange, registerOnTouched, setDisabledState) required to integrate with Angular forms.
  • Form Controls: Inside CustomFormComponent, FormGroup manages textInput and checkboxInput.
  • Binding: formControlName="customControl" in the parent template binds CustomFormComponent to parentForm's customControl.
  • Provider: In CustomFormComponent, NG_VALUE_ACCESSOR is provided to enable ControlValueAccessor functionality.

This example demonstrates a basic implementation. Depending on your requirements, you may need to handle additional scenarios such as validation, handling custom events, or integrating with more complex form structures.

Examples

  1. Implementing ControlValueAccessor for a custom form control

    • Description: Create a custom Angular form control that implements ControlValueAccessor to work with ngModel and FormControl.
    • Code:
      import { Component, forwardRef } from '@angular/core'; import { NG_VALUE_ACCESSOR, ControlValueAccessor } from '@angular/forms'; @Component({ selector: 'app-custom-control', template: ` <input type="text" [(ngModel)]="value"> <input type="text" [(ngModel)]="value2"> `, providers: [ { provide: NG_VALUE_ACCESSOR, useExisting: forwardRef(() => CustomControlComponent), multi: true } ] }) export class CustomControlComponent implements ControlValueAccessor { value: string; value2: string; writeValue(value: any) { if (value) { this.value = value.value1; this.value2 = value.value2; } } registerOnChange(fn: any) { this.onChange = fn; } registerOnTouched(fn: any) { this.onTouched = fn; } onChange: any = () => {}; onTouched: any = () => {}; }
    • Explanation: This component CustomControlComponent implements ControlValueAccessor to handle two-way data binding (ngModel) for two input fields (value and value2).

  2. Passing formControl instances to ControlValueAccessor

    • Description: Configure ControlValueAccessor in Angular to manage multiple formControl instances passed from a parent component.
    • Code:
      import { Component, forwardRef, Input } from '@angular/core'; import { NG_VALUE_ACCESSOR, ControlValueAccessor, FormControl } from '@angular/forms'; @Component({ selector: 'app-multi-control', template: ` <input type="text" [formControl]="control1"> <input type="text" [formControl]="control2"> `, providers: [ { provide: NG_VALUE_ACCESSOR, useExisting: forwardRef(() => MultiControlComponent), multi: true } ] }) export class MultiControlComponent implements ControlValueAccessor { @Input() control1: FormControl; @Input() control2: FormControl; writeValue(value: any) { // Implement if needed } registerOnChange(fn: any) { // Implement if needed } registerOnTouched(fn: any) { // Implement if needed } onChange: any = () => {}; onTouched: any = () => {}; }
    • Explanation: MultiControlComponent receives FormControl instances (control1 and control2) from its parent component and uses them directly in its template.

  3. Handling validation in ControlValueAccessor

    • Description: Manage validation and error handling for multiple formControl instances within a custom Angular form control.
    • Code:
      import { Component, forwardRef, Input } from '@angular/core'; import { NG_VALUE_ACCESSOR, ControlValueAccessor, FormControl } from '@angular/forms'; @Component({ selector: 'app-multi-control', template: ` <input type="text" [formControl]="control1" [class.invalid]="control1.invalid && control1.touched"> <input type="text" [formControl]="control2" [class.invalid]="control2.invalid && control2.touched"> <div *ngIf="control1.invalid && control1.touched">Invalid input</div> <div *ngIf="control2.invalid && control2.touched">Invalid input</div> `, providers: [ { provide: NG_VALUE_ACCESSOR, useExisting: forwardRef(() => MultiControlComponent), multi: true } ] }) export class MultiControlComponent implements ControlValueAccessor { @Input() control1: FormControl; @Input() control2: FormControl; writeValue(value: any) { // Implement if needed } registerOnChange(fn: any) { // Implement if needed } registerOnTouched(fn: any) { // Implement if needed } onChange: any = () => {}; onTouched: any = () => {}; }
    • Explanation: Adds visual validation feedback and error messages for each FormControl (control1 and control2) in MultiControlComponent.

  4. Creating a wrapper component with ControlValueAccessor

    • Description: Wrap multiple form controls with ControlValueAccessor to create a reusable Angular component.
    • Code:
      import { Component, forwardRef } from '@angular/core'; import { NG_VALUE_ACCESSOR, ControlValueAccessor } from '@angular/forms'; @Component({ selector: 'app-custom-wrapper', template: ` <app-multi-control [formControl]="parentForm.get('control1')" [formControl2]="parentForm.get('control2')"></app-multi-control> `, providers: [ { provide: NG_VALUE_ACCESSOR, useExisting: forwardRef(() => CustomWrapperComponent), multi: true } ] }) export class CustomWrapperComponent implements ControlValueAccessor { parentForm: FormGroup; writeValue(value: any) { // Implement if needed } registerOnChange(fn: any) { // Implement if needed } registerOnTouched(fn: any) { // Implement if needed } onChange: any = () => {}; onTouched: any = () => {}; }
    • Explanation: CustomWrapperComponent integrates MultiControlComponent and manages its FormControl instances (control1 and control2) through a parent FormGroup.

  5. Binding initial values to ControlValueAccessor

    • Description: Initialize values for multiple form controls managed by ControlValueAccessor in an Angular component.
    • Code:
      import { Component, forwardRef, Input } from '@angular/core'; import { NG_VALUE_ACCESSOR, ControlValueAccessor, FormControl } from '@angular/forms'; @Component({ selector: 'app-multi-control', template: ` <input type="text" [formControl]="control1" [value]="control1.value"> <input type="text" [formControl]="control2" [value]="control2.value"> `, providers: [ { provide: NG_VALUE_ACCESSOR, useExisting: forwardRef(() => MultiControlComponent), multi: true } ] }) export class MultiControlComponent implements ControlValueAccessor { @Input() control1: FormControl; @Input() control2: FormControl; writeValue(value: any) { if (value) { this.control1.setValue(value.control1); this.control2.setValue(value.control2); } } registerOnChange(fn: any) { // Implement if needed } registerOnTouched(fn: any) { // Implement if needed } onChange: any = () => {}; onTouched: any = () => {}; }
    • Explanation: MultiControlComponent sets initial values for control1 and control2 based on the provided value.

  6. Implementing a custom value accessor for multiple form controls

    • Description: Create a custom Angular value accessor for managing multiple form controls in a component.
    • Code:
      import { Component, forwardRef, Input } from '@angular/core'; import { NG_VALUE_ACCESSOR, ControlValueAccessor, FormControl } from '@angular/forms'; @Component({ selector: 'app-multi-control', template: ` <input type="text" [formControl]="control1"> <input type="text" [formControl]="control2"> `, providers: [ { provide: NG_VALUE_ACCESSOR, useExisting: forwardRef(() => MultiControlComponent), multi: true } ] }) export class MultiControlComponent implements ControlValueAccessor { @Input() control1: FormControl; @Input() control2: FormControl; writeValue(value: any) { if (value) { this.control1.setValue(value.control1); this.control2.setValue(value.control2); } } registerOnChange(fn: any) { this.onChange = fn; } registerOnTouched(fn: any) { this.onTouched = fn; } onChange: any = () => {}; onTouched: any = () => {}; }
    • Explanation: MultiControlComponent implements ControlValueAccessor to synchronize values of control1 and control2 with the parent form.

  7. Handling changes in ControlValueAccessor

    • Description: Implement change detection for multiple form controls using ControlValueAccessor in Angular.
    • Code:
      import { Component, forwardRef, Input } from '@angular/core'; import { NG_VALUE_ACCESSOR, ControlValueAccessor, FormControl } from '@angular/forms'; @Component({ selector: 'app-multi-control', template: ` <input type="text" [formControl]="control1" (input)="onInputChange()"> <input type="text" [formControl]="control2" (input)="onInputChange()"> `, providers: [ { provide: NG_VALUE_ACCESSOR, useExisting: forwardRef(() => MultiControlComponent), multi: true } ] }) export class MultiControlComponent implements ControlValueAccessor { @Input() control1: FormControl; @Input() control2: FormControl; writeValue(value: any) { if (value) { this.control1.setValue(value.control1); this.control2.setValue(value.control2); } } registerOnChange(fn: any) { this.onChange = fn; } registerOnTouched(fn: any) { this.onTouched = fn; } onChange: any = () => {}; onTouched: any = () => {}; onInputChange() { this.onChange({ control1: this.control1.value, control2: this.control2.value }); } }
    • Explanation: MultiControlComponent triggers onChange when input values change, updating the parent form with new values of control1 and control2.

  8. Passing initial values to ControlValueAccessor

    • Description: Initialize values for multiple form controls managed by ControlValueAccessor in Angular when the component is loaded.
    • Code:
      import { Component, forwardRef, Input } from '@angular/core'; import { NG_VALUE_ACCESSOR, ControlValueAccessor, FormControl } from '@angular/forms'; @Component({ selector: 'app-multi-control', template: ` <input type="text" [formControl]="control1" [value]="initialValues.control1"> <input type="text" [formControl]="control2" [value]="initialValues.control2"> `, providers: [ { provide: NG_VALUE_ACCESSOR, useExisting: forwardRef(() => MultiControlComponent), multi: true } ] }) export class MultiControlComponent implements ControlValueAccessor { @Input() control1: FormControl; @Input() control2: FormControl; @Input() initialValues: { control1: any, control2: any }; writeValue(value: any) { if (value) { this.control1.setValue(value.control1); this.control2.setValue(value.control2); } } registerOnChange(fn: any) { this.onChange = fn; } registerOnTouched(fn: any) { this.onTouched = fn; } onChange: any = () => {}; onTouched: any = () => {}; }
    • Explanation: MultiControlComponent initializes control1 and control2 with initialValues provided by the parent component.

  9. Syncing values between ControlValueAccessor and parent form

    • Description: Ensure bidirectional data binding between ControlValueAccessor and parent form for multiple form controls.
    • Code:
      import { Component, forwardRef, Input } from '@angular/core'; import { NG_VALUE_ACCESSOR, ControlValueAccessor, FormControl } from '@angular/forms'; @Component({ selector: 'app-multi-control', template: ` <input type="text" [formControl]="control1" (input)="onControl1Change($event.target.value)"> <input type="text" [formControl]="control2" (input)="onControl2Change($event.target.value)"> `, providers: [ { provide: NG_VALUE_ACCESSOR, useExisting: forwardRef(() => MultiControlComponent), multi: true } ] }) export class MultiControlComponent implements ControlValueAccessor { @Input() control1: FormControl; @Input() control2: FormControl; writeValue(value: any) { if (value) { this.control1.setValue(value.control1); this.control2.setValue(value.control2); } } registerOnChange(fn: any) { this.onChange = fn; } registerOnTouched(fn: any) { this.onTouched = fn; } onChange: any = () => {}; onTouched: any = () => {}; onControl1Change(value: any) { this.onChange({ ...this.control1.value, control1: value }); } onControl2Change(value: any) { this.onChange({ ...this.control2.value, control2: value }); } }
    • Explanation: MultiControlComponent updates onChange with new values when control1 and control2 change, ensuring synchronization with the parent form.

  10. Handling disabled state in ControlValueAccessor

    • Description: Manage disabled state for multiple form controls managed by ControlValueAccessor in Angular.
    • Code:
      import { Component, forwardRef, Input } from '@angular/core'; import { NG_VALUE_ACCESSOR, ControlValueAccessor, FormControl } from '@angular/forms'; @Component({ selector: 'app-multi-control', template: ` <input type="text" [formControl]="control1" [attr.disabled]="control1.disabled ? true : null"> <input type="text" [formControl]="control2" [attr.disabled]="control2.disabled ? true : null"> `, providers: [ { provide: NG_VALUE_ACCESSOR, useExisting: forwardRef(() => MultiControlComponent), multi: true } ] }) export class MultiControlComponent implements ControlValueAccessor { @Input() control1: FormControl; @Input() control2: FormControl; writeValue(value: any) { if (value) { this.control1.setValue(value.control1); this.control2.setValue(value.control2); } } registerOnChange(fn: any) { this.onChange = fn; } registerOnTouched(fn: any) { this.onTouched = fn; } onChange: any = () => {}; onTouched: any = () => {}; }
    • Explanation: MultiControlComponent applies the disabled attribute based on control1 and control2 states, reflecting the parent form's disabled state.

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