import oracle.cabo.ui.action.FirePartialAction;
//In the Process Request
OAMessageChoiceBean xx=(OAMessageChoiceBean)webBean.findChildRecursive("xx");
FireAction firePartialAction = new FirePartialAction("xxAction");
xx.setAttributeValue(PRIMARY_CLIENT_ACTION_ATTR,firePartialAction);
Now we will capture this Above Event "xxAction" in the Process From Request Method of the OAF Page Controller.
//In the Process From Request
if("xxAction".equals(pageContext.getParameter(SOURCE_PARAM)))
{
//Event Handling Here
}