3.2. Control Listener

Click Controls provide an action listener mechanism similar to a java.awt.ActionListener.

Click supports two styles of action listeners. The first is using the ActionListener interface and setActionListener(ActionListener) method which provides compile time safety.

The second is to register the action listener via the setListener(Object, String) method where you specify the call back method via its name. This second style uses less lines of code, but has no compile time safety.

Examples of these two action listener styles are provided below:

public class ActionDemo extends BorderPage {

    // Uses listener style 1
    public ActionLink link = new ActionLink();

    // Uses listener style 2
    public ActionButton button = new ActionButton();

    public ActionDemo() {

        // Verbose but provides compile time safety
        link.setActionListener(new ActionListener() {
            public boolean onAction(Control source) {
                return onLinkClick(source);

        // Succinct but typos will cause runtime errors
        button.setListener(this, "onButtonClick");

    // Event Handlers ---------------------------------------------------------

    public boolean onLinkClick(Control source) {
        return true;

    public boolean onButtonClick() {
        return true;

All call back listener methods must return a boolean value. If they return true the further processing of other controls and page methods should continue. Otherwise if they return false, then any further processing should be aborted. By returning false you can effectively exit at this point and redirect or forward to another page. This execution logic is illustrated in the Page Execution Activity Diagram.

Being able to stop further processing and do something else can be very handy. For example your Pages onRender() method may perform an expensive database operation. By returning false in an event handler you can skip this step and render the template or forward to the next page.