'Angular: access FormControl from Directive

I would like to add validators dynamically to my FormControl via a custom Directive.

@Directive({
    selector: "[idNumber]",
})
export class IdNumberDirective implements OnInit {

    constructor(private formControl: FormControl) { }

    ngOnInit() {
        this.addValidators(this.formControl);
    }

    addValidators(formControl: FormControl) {
        formControl.setValidators(Validators.compose(
            [Validators.required,
            Validators.minLength(3),
            Validators.maxLength(8)
            ]
        ));
    }



<mat-form-field>
    <mat-label>{{label}}</mat-label>
    <input matInput
        [formControl]="idNumberFormControl"
        [placeholder]="placeholder"
</mat-form-field>

I don't need to reference the nativeElement (via ElementRef).
I would like to reference the formControl...
...and use it as such:

// HTML with my custom directive 'idNumber' ////////
<custom-input-string
    idNumber 
    [name]="'idNumber'"
    [label]="Id Number"
    [placeholder]="">
</custom-input-string>

// TS ////////
@ViewChild(CustomInputStringComponent) child: CustomInputStringComponent;

ngAfterViewInit() {
    setTimeout(() => {
        this.child.insertIntoForm(this.signupForm);
    }, 0);
}

Any ideas?
Thank you all.

Solution 1:^[1]

Here is an example of using a directive to append validators to your form control.

Stackblitz

Note that using that will result in losing all of your previous validators.

constructor(
  // Get the control directive
  private control: NgControl
) { }
ngOnInit() {
  const abstractControl = this.control.control;
  abstractControl && abstractControl.setValidators([Validators.required]);
}

Solution 2:^[2]

If you utilize NgControl and constructor DI injection we can have a directive applicable to form controls from reactive forms in either formControlName or template driven forms:

Directive:

import { Directive } from "@angular/core";
import { NgControl } from "@angular/forms";

@Directive({
  selector: '[my-directive]'
})
export class MyDirective {
  constructor(private el: ElementRef, private control : NgControl) { }

}

Solution 3:^[3]

The easiest and 'cleanest' way is to use NG_VALIDATORS provider:

import { Directive } from '@angular/core'
import { NG_VALIDATORS ValidationErrors, Validator } from '@angular/forms'

@Directive({
  selector: '[myIdValidator]',
  providers: [
    { provide: NG_VALIDATORS, useExisting: IdValidatorDirective, multi: true }
  ],
})
export class IdValidatorDirective implements Validator {
  validate(control: AbstractControl): ValidationErrors | null {
    // your validation here
    return null
  }
}

Solution 4:^[4]

//TestAnythingsComponent.ts

import { Component, OnInit } from '@angular/core';
import { FormControl, FormBuilder, FormGroup, Validators } from '@angular/forms';
import { IdNumberDirective } from '../directives/IdNumberDirective.directive';

@Component({
  selector: 'app-test-anythings',
  templateUrl: './test-anythings.component.html',
  styleUrls: ['./test-anythings.component.css'],
  providers:[IdNumberDirective]
})
export class TestAnythingsComponent implements OnInit {
  testForm: FormGroup;

  constructor(fb: FormBuilder, IdNumberDirective : IdNumberDirective) { 
    this.testForm = fb.group({
      idNumberFormControl : new FormControl(null,
          Validators.compose([
            Validators.required,
            Validators.minLength(3),
            Validators.maxLength(8),
          IdNumberDirective.customValidator()
          ])
        ),
    })
  }
}

//IdNumberDirective.ts

import { Directive, OnInit } from '@angular/core';
import { Validators, ValidatorFn, AbstractControl, ValidationErrors } from '@angular/forms';

@Directive({
  selector: '[idNumber]'
})
export class IdNumberDirective implements OnInit {

  constructor() {

  }

  ngOnInit() {

  }

  customValidator(): ValidatorFn {
    Validators.nullValidator
    return (control: AbstractControl): ValidationErrors | null => {

      //any condition to check control value
      if (control.value != "Sachin") {
        //return key value pair of errors
        return { "customError": { inValid: true, errMsg: 'Invalid Value' } };
      }
      return null;
    }
  }
}


//test-anythings.component.html



    <form [formGroup]="testForm">
      <input idNumber formControlName="idNumberFormControl" />
      <div *ngIf="testForm.get('idNumberFormControl').invalid && testForm.get('idNumberFormControl').errors.customError.inValid"
        style="color:red">
        {{testForm.get('idNumberFormControl').errors.customError.errMsg}}
      </div>
    
      <button type="submit">submit</button>
    </form>

Solution 5:^[5]

You can access both FormGroup and FormControl in your directive by FormGroupDirective:

NOTE: I'm working on a country selection in this example.

import { FormGroupDirective } from "@angular/forms";

Then:

{
constructor(private fg: FormGroupDirective) { }


// Access the FormGroup
console.log('My FormGroup values: ', this.fg.value);

// Access the FormControl
console.log('The selectedCountryCtrl: ', this.fg.control.controls.selectedCountryCtrl);
console.log('The selectedCountryCtrl value: ', this.fg.control.controls.selectedCountryCtrl.value);

// Access the variable/object directly
console.log('My FormControl selectedCountry value: ', this.fg.value.selectedCountry);
}

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution	Source
Solution 1	Vahid
Solution 2	Suresh Kumar Ariya
Solution 3	mumenthalers
Solution 4
Solution 5	Dharman

'Angular: access FormControl from Directive

Solution 1:[1]

Solution 2:[2]

Solution 3:[3]

Solution 4:[4]

Solution 5:[5]