Wicket in Action

Implement Wicket component visibility changes properly

17 November 2011, by dashorst

Igor mentioned this in a thread on our user mailing list on how to properly implement component visibility changes. I figured that this demanded a greater audience so I took the liberty of republishing his thoughts here.

If the component itself controls its own visibility the best way is to override onConfigure() and call setVisible() inside.

If an outside component controls another's visibility the best way is to override the controlling component's onConfigure() and call controlled.setVisible()

If you have a simple state toggle, like "when i click this link i want this component's visibility to change" then calling component.setVisible() is fine.

If you have a cross-cutting concern (authorization strategy, configure listener, before render listener, etc) overriding component's visibility then call component.setVisibilityAllowed(). Wicket ands this bit with the visible bit to determine final visibility; this way the cross-cutting concern won't dirty component's visibility attribute.

If all of these fail, as a last resort override component.isVisible() but be warned that this has a few pitfalls:

  • it is called multiple times per request, potentially tens of times, so keep the implementation computationally light
  • this value should remain stable across the render/respond boundary. Meaning if isVisible() returns true when rendering a button, but when the button is clicked returns false you will get an error