1.2. Control Listener Type 1 Example

1.2. Control Listener Type 1 Example
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Click includes a library of Controls which provide user interface functionality.

One of the commonly used controls is the ActionLink, which you can use to have an HTML link call a method on a Page object. For example:

public class ControlListenerType1Page extends Page {

    /* Set the listener to this object's "onLinkClick" method. */
    private ActionLink myLink = new ActionLink("myLink", this, "onLinkClick")

    private String msg;

    // Constructor ------------------------------------------------------------

    public ControlListenerType1Page() {
        addControl(myLink); 
    }

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

    /**
     * Handle the ActionLink control click event.
     */
    public boolean onLinkClick() {
        String msg = "ControlListenerPage#" + hashCode()
            + " object method <tt>onLinkClick()</tt> invoked.";
        addModel("msg", msg);

        return true;
    }

}

Add the link to the page. The link will be made available to the page template under the variable myLink, which is the name of the control.

In the Page class we create an ActionLink called myLink and define the control's listener to be the page method onLinkClick(). When a user clicks on myLink control it will invoke the listener method onLinkClick().

In Click a control listener method can have any name but it must return a boolean value. The boolean return value specifies whether processing of page events should continue. This control listener pattern provides a short hand way for wiring up action listener methods without having to define anonymous inner classes.

The advantage of this style of control listener binding is that you have to write fewer lines of code. The disadvantage of this type of control listener binding is that no compile time safety is provided, and you miss out on the compiler refactoring capabilities provided with modern IDEs.

Back to our example, in the page template we define an HTML link and have the myLink control render the link's href attribute:

<html>
  <head>
    <link type="text/css" rel="stylesheet" href="style.css"></link>
  </head>
  <body>
  
  Click myLink control <a href="$myLink.href">here</a>.

  #if ($msg)
    <div id="msgDiv"> $msg </div>
  #end

  </body>
</html>

At runtime this page would be rendered as:

Click myLink control here.

When a user clicks on the link the onLinkClick() method is invoked. This method then creates the msg model value, which is rendered in the page as:

Click myLink control here.

ControlListenerPage#12767107 object method onLinkClick() invoked.