On Fri, 1 Jul 2022 15:16:24 GMT, John Hendrikx <jhendr...@openjdk.org> wrote:
>> This is an implementation of the proposal in >> https://bugs.openjdk.java.net/browse/JDK-8274771 that me and Nir Lisker >> (@nlisker) have been working on. It's a complete implementation including >> good test coverage. >> >> This was based on https://github.com/openjdk/jfx/pull/434 but with a smaller >> API footprint. Compared to the PoC this is lacking public API for >> subscriptions, and does not include `orElseGet` or the `conditionOn` >> conditional mapping. >> >> **Flexible Mappings** >> Map the contents of a property any way you like with `map`, or map nested >> properties with `flatMap`. >> >> **Lazy** >> The bindings created are lazy, which means they are always _invalid_ when >> not themselves observed. This allows for easier garbage collection (once the >> last observer is removed, a chain of bindings will stop observing their >> parents) and less listener management when dealing with nested properties. >> Furthermore, this allows inclusion of such bindings in classes such as >> `Node` without listeners being created when the binding itself is not used >> (this would allow for the inclusion of a `treeShowingProperty` in `Node` >> without creating excessive listeners, see this fix I did in an earlier PR: >> https://github.com/openjdk/jfx/pull/185) >> >> **Null Safe** >> The `map` and `flatMap` methods are skipped, similar to `java.util.Optional` >> when the value they would be mapping is `null`. This makes mapping nested >> properties with `flatMap` trivial as the `null` case does not need to be >> taken into account in a chain like this: >> `node.sceneProperty().flatMap(Scene::windowProperty).flatMap(Window::showingProperty)`. >> Instead a default can be provided with `orElse`. >> >> Some examples: >> >> void mapProperty() { >> // Standard JavaFX: >> label.textProperty().bind(Bindings.createStringBinding(() -> >> text.getValueSafe().toUpperCase(), text)); >> >> // Fluent: much more compact, no need to handle null >> label.textProperty().bind(text.map(String::toUpperCase)); >> } >> >> void calculateCharactersLeft() { >> // Standard JavaFX: >> >> label.textProperty().bind(text.length().negate().add(100).asString().concat(" >> characters left")); >> >> // Fluent: slightly more compact and more clear (no negate needed) >> label.textProperty().bind(text.orElse("").map(v -> 100 - v.length() + >> " characters left")); >> } >> >> void mapNestedValue() { >> // Standard JavaFX: >> label.textProperty().bind(Bindings.createStringBinding( >> () -> employee.get() == null ? "" >> : employee.get().getCompany() == null ? "" >> : employee.get().getCompany().getName(), >> employee >> )); >> >> // Standard JavaFX + Optional: >> label.textProperty().bind(Bindings.createStringBinding( >> () -> Optinal.ofNullable(employee.get()) >> .map(Employee::getCompany) >> .map(Company::getName) >> .orElse(""), >> employee >> )); >> >> // Fluent: no need to handle nulls everywhere >> label.textProperty().bind( >> employee.map(Employee::getCompany) >> .map(Company::getName) >> .orElse("") >> ); >> } >> >> void mapNestedProperty() { >> // Standard JavaFX: >> label.textProperty().bind( >> Bindings.when(Bindings.selectBoolean(label.sceneProperty(), >> "window", "showing")) >> .then("Visible") >> .otherwise("Not Visible") >> ); >> >> // Fluent: type safe >> label.textProperty().bind(label.sceneProperty() >> .flatMap(Scene::windowProperty) >> .flatMap(Window::showingProperty) >> .orElse(false) >> .map(showing -> showing ? "Visible" : "Not Visible") >> ); >> } >> >> Note that this is based on ideas in ReactFX and my own experiments in >> https://github.com/hjohn/hs.jfx.eventstream. I've come to the conclusion >> that this is much better directly integrated into JavaFX, and I'm hoping >> this proof of concept will be able to move such an effort forward. > > John Hendrikx has updated the pull request with a new target base due to a > merge or a rebase. The incremental webrev excludes the unrelated changes > brought in by the merge/rebase. The pull request contains 27 additional > commits since the last revision: > > - Merge branch 'openjdk:master' into feature/fluent-bindings > - Add null checks in Subscription > - Update copyrights > - Move private binding classes to com.sun.javafx.binding package > - Add note to Bindings#select to consider ObservableValue#flatMap > - Fix bug invalidation bug in FlatMappedBinding > > Also fixed a secondary issue where the indirect source of the binding > was unsubscribed and resubscribed each time its value was recomputed. > > Add additional comments to clarify how FlatMappedBinding works. > > Added test cases for these newly discovered issues. > - Fix typos in LazyObjectBinding > - Rename observeInputs to observeSources > - Expand flatMap javadoc with additional wording from Optional#flatMap > - Add since tags to all new API > - ... and 17 more: https://git.openjdk.org/jfx/compare/cdb2f0a8...d66f2ba6 > Let's say we introduce a marker interface that represents a thread-safety > guarantee with regards to `addListener` and `removeListener`: > > ```java > interface ConcurrentListenerAccess {} > ``` > > Now we can use the existing `Disposer` mechanism to automatically schedule > listeners to be removed from `ConcurrentListenerAccess` implementations when > the bound property is eligible for collection. > > It's sufficient to implement `ConcurrentListenerAccess` for > `LazyObjectBinding` to make `map` and `flatMap` work the way I'd expect it to > work. You mean by `Disposer` something like `com.sun.prism.impl.Disposer`? I see that it has a `ReferenceQueue` in it, so I'm guessing that's the mechanism you are referring to. How would you want this triggered? I think a thread blocking on the queue might be best. I think this is a very nice idea to potentially tackle this problem. ------------- PR: https://git.openjdk.org/jfx/pull/675
