AjaxPing.java

package er.ajax;

import com.webobjects.appserver.WOComponent;
import com.webobjects.appserver.WOContext;

import er.extensions.appserver.ERXWOContext;

/**
 * <p>
 * AjaxPing provides support for refreshing a large content area based on a series of periodic refreshes of a very small
 * area. You provide a cache key that upon changing, triggers the update of another target AjaxUpdateContainer.
 * </p>
 * <p>
 * For instance, if you have a list of blog entries, you might refresh the blog entries container with a cache key
 * "blogEntries.count". When the count of the blog entries changes, the entire container will be refreshed.
 * </p>
 * 
 * @binding frequency the frequency of refresh (in millis), defaults to 3000
 * @binding targetContainerID the ID of the update container to refresh when a change is detected
 * @binding cacheKey some hash value that represents the state of the target container
 * @binding onBeforeUpdate (optional) the javascript function to call before updating (should return true if the update
 *          should happen, false if not)
 * @binding id (optional) the id of the ping update container (set this if you want to attach an AjaxBusyIndicator)
 * @binding stop (optional) if true, the ping will stop.  If false, the ping will run.  It's up to you to refresh the ping's container to get it running again after the binding changes from false to true.  
 * 
 * @author mschrag
 */
public class AjaxPing extends WOComponent {
	/**
	 * Do I need to update serialVersionUID?
	 * See section 5.6 <cite>Type Changes Affecting Serialization</cite> on page 51 of the 
	 * <a href="http://java.sun.com/j2se/1.4/pdf/serial-spec.pdf">Java Object Serialization Spec</a>
	 */
	private static final long serialVersionUID = 1L;

	private String _id;

	public AjaxPing(WOContext context) {
		super(context);
	}

	@Override
	public boolean synchronizesVariablesWithBindings() {
		return false;
	}

	/**
	 * Returns the frequency of refresh in millis.
	 * 
	 * @return the frequency of refresh in millis
	 */
	public Object frequency() {
		Object frequency = valueForBinding("frequency");
		if (frequency == null) {
			frequency = "3000";
		}
		return frequency;
	}

	/**
	 * Returns the ID of the ping container.
	 * 
	 * @return the ID of the ping container
	 */
	public String id() {
		if (_id == null) {
			_id = (String) valueForBinding("id");
			if (_id == null) {
				_id = ERXWOContext.safeIdentifierName(context(), true);
			}
		}
		return _id;
	}
}