Hi guys, I was wondering how can I validate a field list, I saw many examples but using form, and I need to validate this field and use it inside a GriedField:

 $fields = FieldList::create(
      $categories=DropdownField::create('ParentCat','Categoria',array(""=>"Seleccionar",1=>"Para Comprar",2=>"Para Disfrutar")),
      $subcat=TextField::create('Title','Subcategoria'),
      $icon=TextField::create('Icon','Icono'),
      TextField::create('BackgroundColor','Fondo categoria')
    );
  //I have tried this, but how to trigger it?
 $validator=new RequiredFields('ParentCat');
return $fields

Thanks in advanced.

public function getCMSFields() {
	//DropdownField::create('ParentCat');
}

public function getCMSValidator() {
	$valid = new RequiredFields();
	$valid->addRequiredField('ParentCat');
	return $valid;
}

I really appreciate your help Devlin, thank u very much man!
I'll leave the complete code here if any one have the same question.

class GaleriaInicio extends DataObject {
  private static $db = array (
    'Title' => 'Varchar'
  );
 public function getCMSValidator(){
    $valid=new RequiredFields();
    $valid->addRequiredField('Title');
    return $valid;
  }

  public function getCMSFields() {
    $fields = FieldList::create(
      TextField::create('Title','Titulo'),
      $uploader = UploadField::create('Photo')
    );
    return $fields;
  }
}