[[how-to-implement-a-spellchecker]]
= How to implement a spellchecker?

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From this link:http://isis.markmail.org/thread/dduarjscrbnodfsi[thread] on the Apache Isis users mailing list:

* _What is the easiest way to add a spell checker to the text written in a field in
   a domain object, for instance to check English syntax?_

One way to implement is to use the xref:refguide:applib:index/services/eventbus/EventBusService.adoc[event bus]:

* Set up a xref:refguide:applib-classes:events.adoc#domain-event-classes[domain event] subscriber that can veto the changes.

* if the change is made through an action, you can use xref:refguide:applib:index/annotation/Action.adoc#domainEvent[@Action#domainEvent].

if if the change is made through an edit, you can use xref:refguide:applib:index/annotation/Property.adoc#domainEvent[@Property#domainEvent].

You'll need some way to know which fields should be spell checked.  Two ways spring to mind:

* either look at the domain event's identifier

* or subclass the domain event (recommended anyway) and have those subclass events implement some sort of marker interface, eg a `SpellCheckEvent`.

And you'll (obviously) also need some sort of spell checker implementation to call.

