[news.eclipse.tools.emf] Re: Stateful vs Singleton

[Ed Merks <Ed.Merks@xxxxxxxxx>]

Conor,

They're cached

Conor O'Mahony wrote:
> Hi Ed,
>
> Thanks for your help. How do I flush the cache? I tried changing the 
> getPropertyDescriptors() method in my XXXItemProvider class to clear 
> the itemProvider list but this method is still only called once when 
> the Item Provider pattern is Singleton.
It's called each time the descriptors are needed, but the value is 
cached in itemPropertyDescriptors and the code is guarded to test for 
null.  So setting itemPropertyDescriptors to null before calling super 
will force it to be recomputed.
> Many thanks,
> Conor
>
> Ed Merks wrote:
> > Conor,
> >
> > Comments below.
> >
> > Conor O'Mahony wrote:
> > > Hi,
> > >
> > > I was looking for a way to filter the properties of my emf objects 
> > > in the properties view, depending on certain conditions of the 
> > > object being shown. By editing the getPropertyDescriptors() method 
> > > in the xxxItemProvider class I was able to select which properties 
> > > descriptors I wanted to add, but this method was only being called 
> > > once per type.
> > Instead of caching it, you could recompute it each time it's called.
> > > I figured by changing the Provider Type to Stateful instead of 
> > > Singleton it would solve this problem and it did. The EMF book says 
> > > that this "doubles the number of objects in the application" 
> > > therefore presumably impacting performance, so my questions are -
> > > 1. Should I avoid doing this and if so is there an alternative 
> > > solution?
> > Yes, just don't cache the descriptors.  Or flush the cache every 
> > thing the argument object is different from the last time.
> > > 2. If I stick to this solution are there any other repercussions I 
> > > should be aware of, will it change how my application currently 
> > > works in any way?
> > Not really no.  Just more adapters...
> > > I am using
> > > Eclipse 3.3 (planning to move to 3.4)
> > > EMF 2.3
> > >
> > > Many thanks for your help,
> > > Conor