The new operation returns a new ObservableValue that is only meaningfully "exists" when the condition holds. If the condition doesn't hold, the effect is as if the operation wasn't invoked at all, i.e. it doesn't meaningfully exist.
With this in mind, here's another option: label.textProperty().bind(longLivedProperty.withScope(container::isShownProperty)); On Mon, Nov 14, 2022 at 3:53 PM John Hendrikx <john.hendr...@gmail.com> wrote: > > Hi, > > I'm working on https://github.com/openjdk/jfx/pull/830 where I asked for > some opinions on the naming of a new method I'd like to introduce in > ObservableValue. > > I wrote a (perhaps too large) comment about the possible names and > rationales: https://github.com/openjdk/jfx/pull/830#issuecomment-1304846220 > > I'd like to ask what others think what would be a good name for this new > method (Observable#when in the PR) in order to move the PR forward, as I > think it offers a very compelling feature to JavaFX (moving from weak > reference to deterministic behavior when it comes to listener > management). My opinion has always been that using weak listeners for > listener management is a crutch that relies far too much on the internal > workings of the JVM and Garbage Collector which offer no guarantees as > to the timely clean up of these references and the listeners related to > them. > > Leading contenders are (but not limited to these, if you have a better > name): > > 1) conditionOn > > 2) updateWhen > > 3) when > > 4) whenever > > Usage in code is nearly always going to be something like these constructs: > > // keeps text property in sync with longLivedProperty when label > is shown: > label.textProperty().bind(longLivedProperty.**when**(label::isShownProperty)); > > // keeps text property in sync with longLivedProperty when > container is shown: > label.textProperty().bind(longLivedProperty.**when**(container::isShownProperty)); > > > It can also be used to make a listener only actively listen when a > condition is met (the listener is added/removed immediately when the > condition changes, facilitating GC): > > // listen to changes of longLivedProperty when container is shown: > longLivedProperty.when(container::isShownProperty) > .addListener((obs, old, current) -> { ... change listener > ... }); > > Or it can be used to disable updates temporarily (or permanently): > > BooleanProperty allowUpdates = new SimpleBooleanProperty(true) > > // keeps text property in sync when updates are allowed: > name.textProperty().bind(model.title.when(allowUpdates)); > detail.textProperty().bind(model.subtitle.when(allowUpdates)); > asyncImageProperty.imageHandleProperty().bind(model.imageHandle.when(allowUpdates)); > > This last example can be useful in Skin#dispose, but has uses outside of > skins as well, for example when you want to prevent updates until things > have settled down. > > Thanks for reading! > > --John > >
