ngOnChanges

Source

void ngOnChanges(Map<String, SimpleChange> changes) {
  _checkFormPresent();
  if (changes.containsKey('form')) {
    var sync = composeValidators(_validators);
    this.form.validator = Validators.compose([form.validator, sync]);
    var async = composeAsyncValidators(_asyncValidators);
    form.asyncValidator =
        Validators.composeAsync([form.asyncValidator, async]);
    form.updateValueAndValidity(onlySelf: true, emitEvent: false);
  }
  _updateDomValue();
}