Thursday, July 10, 2008

Metawidget and Rebinding

One of the cool features of Metawidget is automatic binding between the business model and the UI, using whatever technologies the underlying platform supports (such as BeansBinding).

Up until now, however, there has been a bit of a 'gotcha' with this.

For Metawidgets that don't use automatic binding, the general approach is to call setToInspect and then setValue to populate the generated UI from business model values. This technique has an implicit side effect: the values can also be repopulated as many times as you like with new source objects, without re-calling setToInspect. This allows the Metawidget to be generated once and reused many times, mitigating the performance cost of generation.

For Metawidgets that do use automatic binding, however, setValue is never used. Setting new values requires re-calling setToInspect (and re-running generation) for every new source object.

To avoid this the new release of Metawidget supports a second, lightweight version of setToInspect called rebind. This function is only relevant when using automatic binding. Using rebind, a Metawidget can update the values in its generated widgets without re-running generation. This allows the Metawidget to be generated once and reused many times.

The downside of rebind is that the rebound source object must have exactly the same set of field names as the original object, else the call will fail. It becomes the responsibility of the caller to ensure this consistency.

For an example of rebinding, see the GWT Address Book sample application.

2 comments:

Kyle said...

Does this rebinding still work in metawidget 3.7?

Richard Kennard said...

Yes! The GWT Address Book example is still using rebinding in 3.7. There are no plans to change that.