Proposal. Forms validations directive

In order to add validation error state we has-danger, form-control-danger and form-control-feedback css classes on different html elements

<div class="form-group has-danger">
   <label class="form-control-label" for="title">Title</label>
   <input type="text" class="form-control form-control-danger" formControlName="title" id="title">
   <div class="form-control-feedback">Title is required</div>
</div>

With angular it looks something like this

<div class="form-group" [ngClass]="{'has-danger': adForm.controls.title.invalid && adForm.controls.title.touched}">
   <label class="form-control-label" for="title">Title</label>
   <input type="text" class="form-control" [ngClass]="{'form-control-danger': adForm.controls.title.invalid && adForm.controls.title.touched}" formControlName="title" id="title">
   <div *ngIf="adForm.controls.title.invalid && adForm.controls.title.touched" class="form-control-feedback">Title is required</div>
</div>

I’m thinking about writing few directives to automatically handle all these css classes states so it can look as simple as this:

<div ngbFormGroup>
   <label for="title">Title</label>
   <input type="text" ngbFormControl formControlName="title" id="title">
   <div ngbFormControlFeedback>Title is required</div>
</div>

[Juchar]

Just for other people stumbling across this, I was in the same situation and had to update the approach of @jnizet for the new bootstrap version:

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

@Directive({
  selector: '.form-control:not([ngbNoFormControlValidation]),[ngbFormControlValidation]'
})
export class NgbFormControlValidation {

  @ContentChild(NgControl)
  ngControl: NgControl;

  @HostBinding('class.is-invalid')
  @HostBinding('class.was-validated')
  get isInvalid() {
    return this.ngControl && this.ngControl.dirty && this.ngControl.invalid;
  }
}

Note: This does not take into account the “is-valid” state where green borders are added as I don’t need this right now.

[lonix1]

ng-bootstrap-form-validation library does this automatically