On Mon, 10 Jan 2022 21:09:15 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 >> )); >> >> // 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 incrementally with one additional > commit since the last revision: > > Fix grammar mistakes and did some small rephrases The `LazyObjectBindingTest` tests look good. I was thinking about adding a test that checks the `compyteValue` calls when a listener is attached (should increase) and when not attached (should not increase), but I think this behavior is already tested in `ObjectBinding` itself, so I'll leave it to you. modules/javafx.base/src/main/java/javafx/beans/value/LazyObjectBinding.java line 91: > 89: * > 90: * As the binding must be valid after it becomes observed the > first time > 91: * 'get' is called again. Maybe add an `@link` to `ExpressionHelper` where the validation happens before listener registration, for clarity. modules/javafx.base/src/test/java/test/javafx/beans/value/LazyObjectBindingTest.java line 86: > 84: * valid because it is not yet considered "observed" as the > 85: * computeValue call occurs in the middle of the listener > 86: * registration process. I would add a link to `LazyObjectBinding#updateSubcriptionAfterAdd` where the 2nd call happens. ------------- PR: https://git.openjdk.java.net/jfx/pull/675
