On Fri, 15 Jul 2022 09:23:20 GMT, John Hendrikx <jhendr...@openjdk.org> wrote:
>> This PR adds a new (lazy*) property on `Node` which provides a boolean which >> indicates whether or not the `Node` is currently part of a `Scene`, which in >> turn is part of a currently showing `Window`. >> >> It also adds a new fluent binding method on `ObservableValue` dubbed `when` >> (open for discussion, originally I had `conditionOn` here). >> >> Both of these together means it becomes much easier to break strong >> references that prevent garbage collection between a long lived property and >> one that should be shorter lived. A good example is when a `Label` is bound >> to a long lived property: >> >> >> label.textProperty().bind(longLivedProperty.when(label::isShowingProperty)); >> >> The above basically ties the life cycle of the label to the long lived >> property **only** when the label is currently showing. When it is not >> showing, the label can be eligible for GC as the listener on >> `longLivedProperty` is removed when the condition provided by >> `label::isShowingProperty` is `false`. A big advantage is that these >> listeners stop observing the long lived property **immediately** when the >> label is no longer showing, in contrast to weak bindings which may keep >> observing the long lived property (and updating the label, and triggering >> its listeners in turn) until the next GC comes along. >> >> The issue in JBS also describes making the `Subscription` API public, but I >> think that might best be a separate PR. >> >> Note that this PR contains a bugfix in `ObjectBinding` for which there is >> another open PR: https://github.com/openjdk/jfx/pull/829 -- this is because >> the tests for the newly added method would fail otherwise; once it has been >> integrated to jfx19 and then to master, I can take the fix out. >> >> (*) Lazy means here that the property won't be creating any listeners unless >> observed itself, to avoid problems creating too many listeners on >> Scene/Window. > > John Hendrikx has updated the pull request incrementally with one additional > commit since the last revision: > > Rename showing property to shown as it is already used in subclasses modules/javafx.graphics/src/main/java/javafx/scene/Node.java line 1422: > 1420: } > 1421: > 1422: public final ReadOnlyBooleanProperty shownProperty() { Discussion: Note I had to wrap the ObservableValue<Boolean> to become a ReadOnlyBooleanProperty, even though ObservableValue is already read-only and quite usable without the wrapper. I would have preferred to just have the shown property signature be: ObservableValue<Boolean> shownProperty(); Or even better: ObservableValue<Boolean> shown(); However, I think it would not be detected as a JavaFX property then, and it would also break with the tradition that properties are, well, properties. Thoughts? ------------- PR: https://git.openjdk.org/jfx/pull/830
