TableView with many columns poor ui performance

[Kevin Rushforth]

Whether or not the specification of notifying a listener multiple times 
was intentional or driven by the implementation, it is part of the spec, 
and some applications could be relying on it. I do agree that there is 
no guarantee as to the order, which might simplify things. I can think 
of two possible implementations:

1. Use a counter as you mentioned below as a possibility. If you did 
this, you would need to add an additional LinkedHashSet of objects 
containing the Listener and a count. You could initialize that set to 
null and only constructing it in the (rather unlikely) case that a 
listener is added when it is already in the set of listeners. You could 
then test for "if (countSet == null)" in the various operations and do 
the simple thing if it is.

2. Since adding a listener more than once is unlikely, you could switch 
from a LinkedHashSet to an ArrayList the first time that a listener is 
added more than once. You would keep a Collection of listeners, 
initialize it to a LinkedHashSet, and dynamically switch from a 
LinkedHashSet to an ArrayList (copying existing entries) in addListener 
if the collection contains the listener already. This would be simpler 
logic than keeping track of the count for each object.

I would lean towards the second optoin. It gives the desired speed up 
for the common case where we don't add a listener more than once, and in 
the worst case, switches back to what we have today.

-- Kevin


On 2/12/2020 4:03 AM, Danny Gonzalez wrote:
> Hi Jeanette,
>
>
> True, I hadn't read that spec in ObservableValueBase.
> Although that does seem odd behaviour to me. Obviously as the original implementation was using an array I can see how the implementation drove that specification.
>
> Non of the JavaFx unit tests test for that specific case as the unit tests all passed. It would be nice if there was a specific test case for this behaviour.
>
> I would need to store a registration count for each listener to satisfy this requirement.
>
>
>
> On 12 Feb 2020, at 11:34, Jeanette Winzenburg <fastegal at swingempire.de<mailto:fastegal at swingempire.de>> wrote:
>
>
> Zitat von Danny Gonzalez <danny.gonzalez at screamingfrog.co.uk<mailto:danny.gonzalez at screamingfrog.co.uk>>:
>
> Hi Ed,
>
> I have submitted a pull request and the branch is here:
> https://github.com/screamingfrog/jfx/tree/listeners_optimisation
>
>
>
> hmm .. the change seems to be breaking spec of add/remove listeners
>
> "If the same listener is added more than once, then it will be notified more than once".
>
> or what am I missing?
>
>