[news.eclipse.platform] Re: Does jface databinding support treeviewer?

[Matthew Hall <matthall@xxxxxxxxxxxxxxxxx>]

hao wrote:
> > The input is contentProvider.getKnownElements().
> I do not see the elements returned by contentProvider.getKnownElements() 
> are used in the implementation of PersonGroupLabelProvider. It looks 
> like the PersonGroupLabelProvider has not relation with the content 
> provider at all.

contentProvider.getKnownElements is passed to the ListeningLabelProvider 
constructor.  If you look at the code in that constructor, you will see 
that it is calling addListenerTo for each element in the set.  It also 
adds an ISetChangeListener to the set so that future additions / 
removals in the set will result in a call to addListenerTo() / 
removeListenerFrom(), respectively.

This is useful because the set of known elements tells the label 
provider exactly what elements are in the viewer.  The label provider in 
turn adds property change listeners (in the case of beans) to every 
element in the set, so that when those properties change it can update 
the labels in the viewer.  This is the point of the known elements set.

> > You need to implement ITableLabelProvider so that the tree viewer will 
> recognize that your label provider supports columns.
> Why does PersonGroupLabelProvider need to extends 
> ListeneingLabelProvider? Is only implementing ITableLabelProvider enough?
>
> Your explanation is very helpful. Thanks a lot.
>
> Hao

The DataBinding label providers automatically take care of updating 
labels in the viewer when the underlying model changes.  You could 
certainly implement ITableLabelProvider directly, but then you have to 
take care of all these details manually.  In this case, subclassing 
ListeningLabelProvider is convenient because there is already API for 
monitoring the known elements set and there is a clear way to be 
notified of added and removed elements (addListenerTo / removeListenerFrom).

Matthew