Conditional Form Validations for Angular Reactive Form

Question

I'm trying to set conditional form validations on an angular reactive form and need some help.

I have a form control where the user sets their entity type to either Individual or Business

<select formControlName="entity">
  <option [value]="individual">Individual</option>
  <option [value]="business">Business</option>
</select>

I then have form inputs that display or hide based upon what entity is selected:

<div *ngIf="myForm.controls.entity.value == individual>
  <input formControlName="fullName" />
</div>

<div *ngIf="myForm.controls.entity.value == business>
  <input formControlName="businessName" />
</div>

How can I make both inputs required only if the corresponding entity is selected?

Answer 1

You can use the attribute [formControl]="name_of_your_input_control" assuming this html is within a formGroup element

<div [hidden]="isBusiness">
  <input [formControl]="fullName" />
</div>

<div [hidden]="!isBusiness">
  <input [formControl]="businessName" />
</div>

in your ts class :

After you create your form add this :

isBusiness:boolean = false;
//...
this.nameOfYourForm.valueChanges.subscribe((newForm) => {
     this.isBusiness = (newForm.controls.entity.value == 'business');
     if(this.isbusiness){
        this.nameOfYourForm.controls.fullName.setValidators(/*your new validation here*/);
           //set the validations to null for the other input
     }else{       
           this.nameOfYourForm.controls.businessName.setValidators(/*your new validation here*/);
           //set the validations to null for the other input
     } 
});

Notice that I changed your *ngIf to [hidden] as *ngIf will completely remove the controle from your template where [hidden] will just apply a display none.

You can also add a change listener on a specific control instead of the whole form, but the idea is the same.

Answer 2

RXJS is a big part of the angular reactive forms. ReactiveForms has a elegant solution for this problem.

const formGroup= new FormGroup({
    type: new FormControl(), 
    businessForm: new FormGroup({
      businessName: new Formcontrol('')
    }), 
    individualForm:new FormGroup({
      individualName: new Formcontrol('')
    })
}); 

formType$ = this.formGroup.controls['type'].valueChanges; 

<form [formGroup]="formGroup">

   <div formGroupName="businessForm" *ngIf="(formType$ | async) =='business'">       
     <input formControlName="businessName"/>
   </div>

   <div formGroupName="individualForm" *ngIf="(formType$ | async) =='individual'">
     <input formControlName="individualName"/>
   </div>

</form>

Answer 3

I have an other version:

HTML

<select #select formControlName="entity">
  <option  [ngValue]="Individual">Individual</option>
  <option  [ngValue]="Business">Business</option>
</select>
<br>
<div *ngIf="select.value[0]  === '0'">
  <input #input [required]="select.value[0] === '0'" formControlName="fullName" />
  <span *ngIf="!myForm.get('fullName').valid">Invalid</span>
</div>

DEMO