I just wanted to draw some attention to a recent proof of concept I made
in this pull request: https://github.com/openjdk/jfx/pull/434
It is based on the work I did in
https://github.com/hjohn/hs.jfx.eventstream which is in part based on
work done in ReactFX by Tomas Mikula. The PR itself however shares no
code with ReactFX and is
completely written by me.
If there is interest, I'm willing to invest more time in smoothing out
the API and documentation, investigating further how this would interact
with the primitive types and adding unit test coverage (I have extensive
tests, but thesea are written in JUnit 5, so they would require
conversion or JavaFX could move to support JUnit 5).
What follows below is the text of the PR for easy reading. Feedback is
appreciated.
================
This is a proof of concept of how fluent bindings could be introduced to
JavaFX. The main benefit of fluent bindings are ease of use, type safety
and less surprises. Features:
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: #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 or orElseGet.
Conditional Bindings
Bindings can be made conditional using the conditionOn method. A
conditional binding retains its last value when its condition is false.
Conditional bindings donot observe their source when the condition is
false, allowing developers to automatically stop listening to properties
when a certain condition is met. A major use of this feature is to have
UI components that need to keep models updated which may outlive the UI
conditionally update the long lived model only when the UI is showing.
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")
);
}
void updateLongLivedModelWhileAvoidingMemoryLeaks() {
// Standard JavaFX: naive, memory leak; UI won't get garbage collected
listView.getSelectionModel().selectedItemProperty().addListener(
(obs, old, current) ->
longLivedModel.lastSelectedProperty().set(current)
);
// Standard JavaFX: no leak, but stops updating after a while
listView.getSelectionModel().selectedItemProperty().addListener(
new WeakChangeListener<>(
(obs, old, current) ->
longLivedModel.lastSelectedProperty().set(current)
)
);
// Standard JavaFX: fixed version
listenerReference = (obs, old, current) ->
longLivedModel.lastSelectedProperty().set(current);
listView.getSelectionModel().selectedItemProperty().addListener(
new WeakChangeListener<>(listenerReference)
);
// Fluent: naive, memory leak... fluent won't solve this...
listView.getSelectionModel().selectedItemProperty()
.subscribe(longLivedModel.lastSelectedProperty()::set);
// Fluent: conditional update when control visible
// Create a property which is only true when the UI is visible:
ObservableValue<Boolean> showing = listView.sceneProperty()
.flatMap(Scene::windowProperty)
.flatMap(Window::showingProperty)
.orElse(false);
// Use showing property to automatically disconnect long lived model
// allowing garbage collection of the UI:
listView.getSelectionModel().selectedItemProperty()
.conditionOn(showing)
.subscribe(longLivedModel.lastSelectedProperty()::set);
// Note that the 'showing' property can be provided in multiple ways:
// - create manually (can be re-used for multiple bindings though)
// - create with a helper: Nodes.showing(Node node) ->
ObservableValue<Boolean>
// - make it part of the Node class; as the fluent bindings only bind
themselves
// to their source when needed (lazy binding), this won't create
overhead
// for each node in the scene
}
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
