Reacting to mouse events on a TreeCell. Is it supposed to be this awkward?

[Scott Palmer]

FYI.. my first test with Java 8 I get the following exception when I try to
do:

Bindings.select(this.sceneProperty(), "window", "showing").addListener(...

(which may not be necessary on JavaFX 8, but I think I need it for 7u40)

10-08 16:07:22 INFO beans [JavaFX Application Thread]: Property 'window' in
ReadOnlyObjectProperty [bean: BrowserTreeCell at 63eb8c04[styleClass=cell
indexed-cell tree-cell]'null', name: scene, value: null] is null
java.lang.NullPointerException
        at
com.sun.javafx.binding.SelectBinding$SelectBindingHelper.getObservableValue(Unknown
Source)
        at
com.sun.javafx.binding.SelectBinding$AsObject.computeValue(Unknown Source)
        at javafx.beans.binding.ObjectBinding.get(Unknown Source)
        at javafx.beans.binding.ObjectExpression.getValue(Unknown Source)
        at
com.sun.javafx.binding.ExpressionHelper$SingleChange.<init>(Unknown Source)
        at
com.sun.javafx.binding.ExpressionHelper$SingleChange.<init>(Unknown Source)
        at com.sun.javafx.binding.ExpressionHelper.addListener(Unknown
Source)
        at javafx.beans.binding.ObjectBinding.addListener(Unknown Source)


On Tue, Oct 8, 2013 at 4:00 PM, Scott Palmer <swpalmer at gmail.com> wrote:

> Will do.
>
> I also just noticed (after using Bindings.select(this.sceneProperty(),
> "window", "showing") to try to trigger my "diconnecting") that in 7u40
> TreeCells seem to remain connected to the scene until I force the tree to
> repaint.
> In my app every time I open a document I rebuild a tree.  even when
> listening to the above mentioned binding, nothing was triggering as I
> loaded new documents until I resized my UI.  Then suddenly all those unused
> TreeCells were "let go".
>
>
> Scott
>
>
> On Tue, Oct 8, 2013 at 3:48 PM, Jonathan Giles <jonathan.giles at oracle.com>wrote:
>
>> I note right at the end you say you're using 7u40. In the JavaFX 2.x
>> series of releases it is true that TreeView misbehaved a bit around cell
>> reuse. This should no longer be the case in JavaFX 8.0. In any case, the
>> best option is to file a bug report and discuss it further in there,
>> especially so if you can reproduce the issue in JavaFX 8.0.
>>
>> One thing that sticks out: you don't say if you're using
>> WeakEventHandler or EventHandler instances. If you're using EventHandler
>> you could consider using WeakEventHandler. This may help to alleviate
>> some of the memory leak.
>>
>> -- Jonathan
>>
>> On 9/10/2013 8:37 a.m., Scott Palmer wrote:
>> > I'm investigating a memory leak and it seems that the culprit is event
>> > listeners attached to TreeCells
>> >
>> > The GC roots of my leaks are deep in the JavaFX window/event system
>> >
>> > In a class extending TreeCell,  am calling methods on such as:
>> >
>> > setOnContextMenuRequested(contextMenuRequestHandler);
>> > setOnMouseClicked(mouseEventHandler);
>> > setOnDragDetected(dragDetectedHandler);
>> >
>> > All of the event handlers in this case will have a reference to the
>> > TreeCell, either via the implicit reference of the anonymous inner
>> class,
>> > or an explicit member
>> >
>> > I do this in updateItem when the cell is not empty and has a non-null
>> item.
>> > If updateItem is called and the cell is empty or has a null item then I
>> > clear the event handlers with:
>> >
>> > setOnContextMenuRequested(null);
>> > setOnMouseClicked(null);
>> > setOnDragDetected(null);
>> >
>> > The problem is that TreeView doesn't seem to reuse TreeCells very much.
>>  It
>> > mostly creates new ones.  This means that many TreeCells are
>> disconnected
>> > from the scene graph and "lost" while there is still an event handler
>> > connected to it.
>> >
>> > Am I doing something wrong?
>> > This seemed like the correct way to deal with dragging and double
>> clicking
>> > on tree nodes.
>> >
>> > The tutorial here:
>> > http://docs.oracle.com/javafx/2/ui_controls/tree-view.htm#BABDEADA
>> >
>> > only goes so far as to add a context menu. (My context menu needs to be
>> > constructed dynamically.)  So I'm not sure if I'm "allowed" to connect
>> > event handlers to TreeCells in this way, but I don't know what the
>> > alternative is.
>> >
>> > I suppose I would have to listen to something to ensure the TreeCell is
>> > still part of the scene graph and disconnect the listeners when that
>> > changes.  It seems a bit awkward.
>> >
>> >
>> > Scott
>> > (I'm using 7u40)
>>
>>
>