Chapter 9: Behavior Secrets - Power without inheritance

What is Behavior?

A Behavior is a reusable capability attached to a component. It lets you extend rendering and event handling without subclassing every UI element.

Lifecycle

Behaviors participate in configuration, rendering, and detachment phases. This makes them suitable for cross-cutting UI concerns.

Use behaviors to register CSS and JavaScript resources near the components that require them.

Custom Behavior

Example

component.add(new AttributeAppender("class", " highlighted"));

Design Rules

Use behaviors for reusable cross-component concerns.
Avoid storing heavy mutable state in behaviors.
Prefer explicit naming and focused scope.

Practical Pitfalls

Problem
AJAX behavior never fires.

Cause
Event names differ by version and old naming stayed in the code.

Solution
Verify event names against your Wicket version and standardize them.
Problem
Event handling is unstable across repeated interactions.

Cause
DOM timing and JavaScript issues conflict with behavior binding.

Solution
Inspect event propagation and JS errors alongside Wicket behavior code.
Problem
Visibility logic becomes slow and unpredictable.

Cause
Heavy checks are placed in high-frequency visibility evaluation paths.

Solution
Centralize expensive checks in configure phase and keep visibility checks lightweight.