It depends on what you need to recompute. If you invalidate some
properties and the internal layout depends on these properties, then
also your pref/min size depends on these properties.
The layout (simplified) usually works in 3 steps: 1)compute the layout
using min/pref/max size of children (here the compute* methods of child
will be called)
2) children are resized to their width/height depending on the layout
3) layouChildren of a child is called, where these 3 steps are done for
the child, using the newly provided size from step 2
This has several consequences: As compute* methods are called before
layoutChildren, you need to do recomputation there. The recomputed
values can be cached and reused in layoutChildren. The other thing is
that you can't rely on getting exactly pref width/height, so you can
recompute only things that don't depend on actual size of the component.
The exact size will be known in layoutChildren() call.
It would be great to have some invalidate/recompute API that would be
called automatically before compute* and layoutChildren method. I've
filed a JIRA issue for that: https://javafx-jira.kenai.com/browse/RT-34118
-Martin
On 11/06/2013 08:43 AM, Yennick Trevels wrote:
Isn't it somewhat counter-intuitive to perform such changes in one of the
computePref*() methods? You're adding children in a method which is
supposed to compute the preferred width/height.
There should be a better way to do this. In Apache Flex for example,
there's a commitProperties() and updateDisplayList() method in which you
can do these things, which are called somewhat similar to a pulse in JavaFx
(except that you have to invalidate them yourself).
On Tue, Nov 5, 2013 at 8:10 PM, Jonathan Giles <jonathan.gi...@oracle.com>wrote:
You're right in that controls don't tend to use ScenePulseListener. This
may be due to an oversight on our part, or just that our requirements
differ (I don't honestly know).
You're also right that it is important to batch up property changes and
do them once per pulse, rather than as they come in. If this is not done
you do indeed get a severe performance hit (I remember back in the day
before I optimised many of the controls in this way, the performance
impact of not doing this was staggering).
The way I do it is simple: in places where I receive events from
properties / bindings / listeners, where I know that there is
potentially a lot of changes coming through, I create a boolean (e.g.
'refreshView' or somesuch). I then set this boolean to true, and in the
appropriate place in the code (most commonly layoutChildren(), but
sometimes in the computePref*() methods), I start the method with code
like this:
if (refreshView) {
doExpensiveOperationThatShouldHappenOnlyOncePerPulse();
refreshView = false;
}
The reason why I sometimes use layoutChildren() and sometimes the
computePref*() methods comes down to the (new) rule in JavaFX 8.0 that
you can not change the children list of a node within the
layoutChildren() method. Because of this, if I need to modify the
children list, I put the above code in the computePref*() method.
I hope that helps.
-- Jonathan
On 6/11/2013 3:58 a.m., John Hendrikx wrote:
Hi List,
I'm considering using a ScenePulseListener to avoid expensive
recalculations when multiple bindings trigger an action.
My problem is this:
I like to build Views (Controls) that are dumb and expose properties
that can be manipulated by whatever is using the View. The View
listens to its own Properties and adjusts its state accordingly. Some
of these adjustments are related (like width + height) and can be
expensive when calculated immediately. So I would like to mark the
View as "invalid" and recalculate its state (if invalid) on the next
Pulse.
My current use case I'm looking at is a View that wraps (amongst
others) a TreeView. The View exposes an ObservableList and a
BooleanProperty that decides whether the first level of the Tree
should be displayed as Tabs or as Nodes (which has an impact on what
Nodes actually are added to the TreeView, and which are added as
Tabs). User code will thus often set a new list of nodes + change the
boolean to show tabs or nodes. The View currently naively has
InvalidationListeners on both of these properties which cause
TreeNodes to be created after the first change... then discarded and
recreated after the second change by the user code, ie:
view.nodesProperty().setAll(nodes); // Recreates all
Tabs/TreeNodes with the current value of expand top level, as we donot
know another change might be incoming...
view.expandTopLevelProperty().set(false); // Recreates all
Tabs/TreeNodes again if expand top level was changed...
This specific problem might be done in a better way, but the point
remains, how do I avoid expensive calculations when multiple
properties get changed one after the other by the user code? I'm
assuming that JavaFX controls already avoid these kinds of things, and
I'd like to know whether using a ScenePulseListener is the way to go,
or that it can/should be done in a different way -- examining the code
for TreeView (and its superclasses), I couldn't find uses of
ScenePulseListener...
--John
