JsOrb

Event Listeners

Each property of your POJOs has listener support. That is, for a property foo there's a method addFooListener(js.mvc.Listener) and removeFooListener(js.mvc.Listener). You can use these methods in your JavaScript to perform business logic, validations, etc. The event listeners form the foundation of the HTML Bindings code.

js.mvc.Listener

The js.mvc.Listener class is useful for quickly creating a listener that can be called by:

• A POJO when a property is changed
• The remote proxy when a method completes

Creating a listener is easy, and can be done in a number of ways:

Creating a listener with a function

function handleFooChanged() {
        alert("Hey! Who changed foo?");
}

var fooChangedListener = new js.mvc.Listener(handleFooChanged);
var bar = new com.foo.Bar();
bar.addFooChangedListener(fooChangedListener);

In the above example, we simply declare a function handleFooChanged() which is called when the foo attribute is changed. If any state information is required (like which Bar object we're listening to), that state can be added to the listener instance through something like fooChangedListener.bar = bar.

Creating a listener with a closure

var bar = new com.foo.Bar();
bar.addFooChangedListener(new js.mvc.Listener(function() {
    alert("The foo property has changed: " + bar.getFoo());
}));

In this example, our listener can access the bar variable because JavaScript sets up a closure in our anonymous function declaration. Closures are somewhat similar to anonymous inner classes, especially in that they can be the cause of memory leaks if you're not careful how you use them. However, most of the time closures are a wonderful thing.