Im want to display error message to UI when user change the quantity of package entry.

Im firgured out has a way to validate data of CatalogRelationDto by using ICatalogEvents like this:

public void Initialize(InitializationEngine context)
{
	var catalogEvent = ServiceLocator.Current.GetInstance<ICatalogEvents>();
	catalogEvent.RelationUpdating += CatalogEvent_RelationUpdating;
}


private void CatalogEvent_RelationUpdating(object sender, RelationEventArgs e)
{
	if (sender is CatalogRelationDto)
	{
		// TODO: Validate data
		// TODO: Show error message
	}
}

But currently im have no idear to show error message to UI like IValidate behavior.

Does any one have some idear?

Thanks alot.