On 11/07/2013 11:58 AM, John Hendrikx wrote:
On 7/11/2013 09:20, Martin Sladecek wrote:
On 11/06/2013 07:31 PM, John Hendrikx wrote:
On 5/11/2013 20:10, Jonathan Giles 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'm not sure in which circumstances layoutChildren() will be called
or if I can mark my control as needing layout, since the properties
I want to trigger on are not directly attached to anything that
JavaFX will be monitoring. The ScenePulseListener therefore seems
like a good choice -- the reason I'm asking about is that I cannot
find any examples and the documentation for it is also pretty lean.
If you call requestLayout(), the layoutChildren() will be called on
the next pulse. The ScenePulseListener is not a public API and the
layout is the only way how Controls can react on pulse. Can you be
more specific on what you need to do on pulse? If it's not related to
the layout, maybe it would be reasonable to introduce some API that
would allow you to execute code on each pulse.
Hm, I found it googling, and since it showed up here:
http://docs.oracle.com/javafx/2/api/javafx/scene/Scene.ScenePulseListener.html
I figured it was public, but I just noticed the class is defined
package private.
Anyway, what I need to do:
1) I have two listeners that keep an eye on two properties,
expandTopLevel and nodes:
expandTopLevel.addListener(new InvalidationListener() {
@Override
public void invalidated(Observable observable) {
buildTree();
}
});
mediaNodes.addListener(new ListChangeListener<MediaNode>() {
@Override
public void onChanged(ListChangeListener.Change<? extends
MediaNode> change) {
buildTree();
}
});
2) buildTree() will call TreeView#setRoot() directly/indirectly in
both cases, either with the full list of nodes or a subtree, depending
on expandTopLevel state. The other possible subtree choices are moved
into a tab-like control, which will have either 1 tab (if not
expandTopLevel) or multiple tabs (one for each top level node).
Now, TreeView itself might be smart enough now to actually draw the
sets of Nodes twice when both properties change, however buildTree
will still get called twice, which itself is doing quite some work
(although not enough to move it off the event thread), but also can
cause things like selection to change.
None of this will affect the size of these controls, which I assumed
would mean layoutChildren() does not get called (definitely not on the
Pane containing both the tab-like control and the TreeView control).
Also, if I donot call buildTree, but "wait", I'd at the very least
would need to change something to trigger a layout -- requestLayout()
would work me there.
The layout is not only about different preferred size. In your custom
Control, stable preferred size just means, the parent of this control
doesn't need to relayout. But internally, I would recommend you to
modify the properties of children in layoutChildren() method. This
means, instead of buildTree, call requestLayout() and call buildTree()
inside of layoutChildren(). Since, as you say, no changes to preferred
size will happen, you don't need to do any special computation in
compute* methods.
-Martin
--John
-Martin
I'll experiment with a ScenePulseListener and see how it pans out,
it looks like it would be an elegant solution.
Thanks Jonathan!
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
