On Fri, 15 Jul 2022 09:03:35 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. modules/javafx.base/src/main/java/javafx/beans/value/ObservableValue.java line 311: > 309: * @since 20 > 310: */ > 311: default ObservableValue<T> when(ObservableValue<Boolean> condition) { Discussion: name? `when`, `conditionOn`, other suggestions? Note that this is not the same as a possible future method `filter`, as a `filter` would still keep observing its source at all times (and would use a `Predicate` as parameter). modules/javafx.graphics/src/main/java/javafx/scene/Node.java line 1422: > 1420: } > 1421: > 1422: public final ReadOnlyBooleanProperty showingProperty() { 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 showing property signature be: ObservableValue<Boolean> showingProperty(); 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
