Read the free eBook Learning RxJava with JavaFX to get started!

Learn more about RxJava on the Wiki Home and the Netflix TechBlog post where RxJava was introduced.

RxJavaFX is a simple API to convert JavaFX events into RxJava Observables and vice versa. It also has a scheduler to safely move emissions to the JavaFX Event Dispatch Thread.

NOTE: To use with Kotlin, check out RxKotlinFX to leverage this library with extension functions and additional operators.

##Documentation Learning RxJava with JavaFX (EAP)

• Google Group: RxJava
• Twitter: @RxJava
• GitHub Issues

Binaries and dependency information for Maven, Ivy, Gradle and others can be found at http://search.maven.org.

Example for Maven:

<dependency>
    <groupId>io.reactivex</groupId>
    <artifactId>rxjavafx</artifactId>
    <version>x.y.z</version>
</dependency>

Gradle:

dependencies {
	compile 'io.reactivex:rxjavafx:x.y.z'
}

Ivy:

<dependency org="io.reactivex" name="rxjavafx" rev="x.y.z" />

To build:

$ git clone git@github.com:ReactiveX/RxJavaFX.git
$ cd RxJavaFX/
$ ./gradlew build

RxJavaFX has a comprehensive set of features to interop RxJava with JavaFX:

• Factories to turn Node, ObservableValue, ObservableList, and other component events into an RxJava Observable
• Factories to turn an RxJava Observable into a JavaFX Binding.
• A scheduler for the JavaFX dispatch thread

###Node Events You can get event emissions by calling JavaFxObservable.eventsOf() and pass the JavaFX Node and the EventType you are interested in. This will return an RxJava Observable.

Button incrementBttn = new Button("Increment");

Observable<ActionEvent> bttnEvents =
        JavaFxObservable.eventsOf(incrementBttn, ActionEvent.ACTION);

###Action Events Action events are common and do not only apply to Node types. They also emit from MenuItem and ContextMenu instances, as well as a few other types.

Therefore, a few overloaded factories are provided to emit ActionEvent items from these controls

#####Button ActionEvents

Button incrementBttn = new Button("Increment");

Observable<ActionEvent> bttnEvents =
        JavaFxObservable.actionEventsOf(incrementBttn);

#####MenuItem ActionEvents

MenuItem menuItem = new MenuItem("Select me");

Observable<ActionEvent> menuItemEvents = 
        JavaFxObservable.actionEventsOf(menuItem);

###Other Event Factories

There are also factories provided to convert events from a Dialog, Window or Scene into an Observable. If you would like to see factories for other components and event types, please let us know or put in a PR.

####Dialogs and Alerts

Alert alert = new Alert(AlertType.CONFIRMATION);
alert.setTitle("Confirmation");
alert.setHeaderText("Please confirm your action");
alert.setContentText("Are you ok with this?");

JavaFxObservable.fromDialog(alert)
    .filter(response -> response.equals(ButtonType.OK))
    .subscribe(System.out::println,Throwable::printStackTrace);

#####Emitting Scene Events

Observable<MouseEvent> sceneMouseMovements =
     JavaFxObservable.eventsOf(scene, MouseEvent.MOUSE_MOVED);

sceneMouseMovements.subscribe(v -> System.out.println(v.getSceneX() + "," + v.getSceneY()));

#####Emitting Window Hiding Events

 Observable<WindowEvent> windowHidingEvents =
    JavaFxObservable.eventsOf(primaryStage,WindowEvent.WINDOW_HIDING);

windowHidingEvents.subscribe(v -> System.out.println("Hiding!"));

###ObservableValue Not to be confused with the RxJava Observable, the JavaFX ObservableValue can be converted into an RxJava Observable that emits the initial value and all value changes.

TextField textInput = new TextField();

Observable<String> textInputs =
        JavaFxObservable.valuesOf(textInput.textProperty());

Note that many Nodes in JavaFX will have an initial value, which sometimes can be null, and you might consider using RxJava's skip() operator to ignore this initial value.

#####ObservableValue Changes

For every change to an ObservableValue, you can emit the old value and new value as a pair. The two values will be wrapped up in a Change class and you can access them via getOldVal() and getNewVal(). Just call the JavaFxObservable.valuesOfChanges() factory.

SpinnerValueFactory<Integer> svf = new SpinnerValueFactory.IntegerSpinnerValueFactory(0, 100);
Spinner spinner = new Spinner<>();
spinner.setValueFactory(svf);
spinner.setEditable(true);

Label spinnerChangesLabel = new Label();
Subscription subscription = JavaFxObservable.changesOf(spinner.valueProperty())
        .map(change -> "OLD: " + change.getOldVal() + " NEW: " + change.getNewVal())
        .subscribe(spinnerChangesLabel::setText);

###ObservableList, ObservableMap, and ObservableSet

There are several factories to emit many useful ObservableList, ObservableMap, and ObservableSet events as Observables. These all can be found as static factory methods in the JavaFxObservable static class.

###Binding You can convert an RxJava Observable into a JavaFX Binding by calling the JavaFxSubscriber.toBinding() factory. Calling the dispose() method on the Binding will handle the unsubscription from the Observable. You can then take this Binding to bind other control properties to it.

Button incrementBttn = new Button("Increment");
Label incrementLabel =  new Label("");

Observable<ActionEvent> bttnEvents =
        JavaFxObservable.eventsOf(incrementBttn, ActionEvent.ACTION);
        
Observable<String> accumulations = bttnEvents.map(e -> 1)
        .scan(0,(x, y) -> x + y)
        .map(Object::toString);
        
Binding<String> binding = JavaFxSubscriber.toBinding(accumulations);

incrementLabel.textProperty().bind(binding);

//do stuff, then dispose Binding
binding.dispose();

It is usually good practice to specify an onError to the Binding, just like a normal Subscriber so you can handle any errors that are communicated up the chain.

incrementLabel.textProperty().bind(binding, e -> e.printStackTrace());

###Lazy Binding

The toBinding() factory above will eagerly subscribe the Observable to the Binding implementation. But if you want to delay the subscription to the Observable until the Binding is actually used (specifically when its getValue() is called), use toLazyBinding() instead.

Binding<String> lazyBinding = JavaFxSubscriber.toLazyBinding(myObservable);

This can be handy for data controls like TableView, which will only request values for records that are visible. Using the toLazyBinding() to feed column values will cause subscriptions to only happen with visible records.

###CompositeBinding

You also have the option to use a CompositeBinding to group multiple Bindings together, and dispose() them all at once. It is the JavaFX equivalent to CompositeSubscription.

Binding<Long> binding1 = ...
bindings.add(binding1);

Binding<Long> binding2 = ... 
bindings.add(binding2);

//do stuff on UI, and dispose() both bindings
bindings.dispose();

###CompositeObservable

In UI development, it is not uncommon to have an event triggered in multiple places, or have inputs coming from multiple UI controls.b You may also want to leverage code separation patterns like MVC, and have the Observables completely separated from their Subscribers in modular fashion. Let's say you want to make a refresh() operation callable from a Button, a MenuItem, and a CTRL + R hotkey combination.

//make refresh Button
Button button = new Button("Refresh");
Observable<ActionEvent> buttonClicks = JavaFxObservable.actionEventsOf(button);

//make refresh MenuItem 
MenuItem menuItem = new MenuItem("Refresh");
Observable<ActionEvent> menuItemClicks = JavaFxObservable.actionEventsOf(menuItem);

//CTRL + R hotkeys on a TableView
TableView<MyType> tableView = new TableView<>();
Observable<ActionEvent> hotKeyPresses =
		JavaFxObservable.eventsOf(tableView, KeyEvent.KEY_PRESSED)
			.filter(ke -> ke.isControlDown() && ke.getCode().equals(KeyCode.R))
			.map(ke -> new ActionEvent());
			

If you have all three components accessible in advance, you could use Observable.merge() to merge them all together.

Observable.merge(buttonClicks, menuItemClicks, hotKeyPresses)
		.subscribe(ae -> refresh());

But this is preferable only if all the declarations are easily accessible. If they are in separate places throughout your UI code, this is problematic. Complex UI's are likely to be highly decoupled and have a model backing all the event flows. You cannot "add" and "remove" Observables in an Observable.merge() operation, and this can make designing the model rather frustrating.

At this point, you may be tempted to resort to a Subject to act as a sort of event bus accepting inputs from any number of sources and outputs to any number of subscribers. Although this is a valid use case, Subjects are prone to abuse and can introduce many antipatterns.

Introducing the CompositeObservable. It is a tighter, safer alternative to a Subject or an event bus. You can add() and remove() Observables at any time from a CompositeObservable, and this is useful to put in an event model backing the application.

class MyEventModel {
    
    private final CompositeObservable<ActionEvent> refreshRequests = new CompositeObservable<>();
    
    public CompositeObservable<ActionEvent> getRefreshRequests() {
        return refreshRequests;
    }
}

Wherever the three controls are declared, you can add() the Observable<ActionEvent> from each control to the CompositeObservable<ActionEvent>. It will then merge them. You can then call the toObservable() to subscribe wherever those events are needed.

//make refresh Button
Button button = new Button("Refresh");
Observable<ActionEvent> buttonClicks = JavaFxObservable.actionEventsOf(button);
myEventModel.getRefreshRequests().add(buttonClicks);


//make refresh MenuItem
MenuItem menuItem = new MenuItem("Refresh");
Observable<ActionEvent> menuItemClicks = JavaFxObservable.actionEventsOf(menuItem);
myEventModel.getRefreshRequests().add(menuItemClicks);


//CTRL + R hotkeys on a TableView
TableView<MyType> tableView = new TableView<>();

Observable<ActionEvent> hotKeyPresses =
    JavaFxObservable.eventsOf(tableView, KeyEvent.KEY_PRESSED)
        .filter(ke -> ke.isControlDown() && ke.getCode().equals(KeyCode.R))
        .map(ke -> new ActionEvent());

myEventModel.getRefreshRequests().add(hotKeyPresses);

//subscribe to refresh events
myEventModel.getRefreshRequests().toObservable().subscribe(ae -> refresh());

The add() method on a CompositeObservable returns a subscription which you can unsubscribe(), and this will affect all existing downstream Subscribers. For UI development, this is good because there is no sensitivity to the order of adding Observables and subscribing.

Of course, you can pass around any type T in a CompositeObservable<T> and not just ActionEvent. It can be = helpful to pass around entire data structures, such as CompositeObservable<Set<MyType>>, to relay requests and inputs between controls.

You also have the option to pass a Transformer to the CompositeObservable constructor, and this will be applied to the Observable returned from toObservable(). This is helpful to apply multicasting or replaying behaviors.

CompositeObservable<String> valueChanges = CompositeObservable<>(obs -> obs.replay(1).refCount());

When you update any JavaFX control, it must be done on the JavaFX Event Dispatch Thread. Fortunately, the JavaFxScheduler makes it trivial to take work off the JavaFX thread and put it back when the results are ready. Below we can use the observeOn() to pass text value emissions to a computation thread where the text will be flipped. Then we can pass JavaFxScheduler.getInstance() to another observeOn() afterwards to put it back on the JavaFX thread. From there it will update the flippedTextLabel.

TextField textInput = new TextField();
Label fippedTextLabel = new Label();

Observable<String> textInputs =
        JavaFxObservable.valuesOf(textInput.textProperty());

sub2 = textInputs.observeOn(Schedulers.computation())
        .map(s -> new StringBuilder(s).reverse().toString())
        .observeOn(JavaFxScheduler.getInstance())
        .subscribe(fippedTextLabel::setText);

###JavaFX Interval

There is a JavaFX equivalent to Observable.interval() that will emit on the JavaFX thread instead. Calling JavaFxObservable.interval() will push consecutive Long values at the specified Duration.

Observable<Long> everySecond = JavaFxObservable.interval(Duration.millis(1000));

##Differences from ReactFX ReactFX is a popular API to implement reactive patterns with JavaFX using the EventStream. However, RxJava uses an Observable and the two are not (directly) compatible with each other.

Although ReactFX has some asynchronous operators like threadBridge, ReactFX emphasizes synchronous behavior. This means it encourages keeping events on the JavaFX thread. RxJavaFX, which fully embraces RxJava and asynchronous design, can switch between threads and schedulers with ease. As long as subscriptions affecting the UI are observed on the JavaFX thread, you can leverage the powerful operators and libraries of RxJava safely.

If you are heavily dependent on RxJava, asynchronous processing, or do not want your entire reactive codebase to be UI-focused, you will probably want to use RxJavaFX.

##Notes for Kotlin If you are building your JavaFX application with Kotlin, check out RxKotlinFX to leverage this library through Kotlin extension functions.

import javafx.application.Application;
import javafx.beans.binding.Binding;
import javafx.event.ActionEvent;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.layout.GridPane;
import javafx.stage.Stage;
import rx.Observable;
import rx.Subscription;
import rx.observables.JavaFxObservable;
import rx.subscribers.JavaFxSubscriber;

public class RxJavaFXTest extends Application {

    private final Button incrementBttn;
    private final Label incrementLabel;
    private final Binding<String> binding1;

    private final TextField textInput;
    private final Label flippedTextLabel;
    private final Binding<String> binding2;

    private final Spinner<Integer> spinner;
    private final Label spinnerChangesLabel;
    private final Subscription subscription;

    public RxJavaFXTest() {

        //initialize increment
        //demoTurns button events into Binding
        incrementBttn = new Button("Increment");
        incrementLabel =  new Label("");

        Observable<ActionEvent> bttnEvents =
                JavaFxObservable.actionEventsOf(incrementBttn);

        binding1 = JavaFxSubscriber.toBinding(bttnEvents.map(e -> 1).scan(0,(x, y) -> x + y)
                .map(Object::toString));

        incrementLabel.textProperty().bind(binding1);

        //initialize text flipper
        //Schedules on computation Scheduler for text flip calculation
        //Then resumes on JavaFxScheduler thread to update Binding
        textInput = new TextField();
        flippedTextLabel = new Label();

        Observable<String> textInputs =
                JavaFxObservable.valuesOf(textInput.textProperty());

        binding2 = JavaFxSubscriber.toBinding(textInputs.observeOn(Schedulers.computation())
                .map(s -> new StringBuilder(s).reverse().toString())
                .observeOn(JavaFxScheduler.getInstance()));

        flippedTextLabel.textProperty().bind(binding2);

        //initialize Spinner value changes
        //Emits Change items containing old and new value
        //Uses RxJava Subscription instead of Binding just to show that option
        SpinnerValueFactory<Integer> svf = new SpinnerValueFactory.IntegerSpinnerValueFactory(0, 100);
        spinner = new Spinner<>();
        spinner.setValueFactory(svf);
        spinner.setEditable(true);

        spinnerChangesLabel = new Label();
        subscription = JavaFxObservable.changesOf(spinner.valueProperty())
                .map(change -> "OLD: " + change.getOldVal() + " NEW: " + change.getNewVal())
                .subscribe(spinnerChangesLabel::setText);

    }

    @Override
    public void start(Stage primaryStage) throws Exception {

        GridPane gridPane = new GridPane();

        gridPane.setHgap(10);
        gridPane.setVgap(10);

        gridPane.add(incrementBttn,0,0);
        gridPane.add(incrementLabel,1,0);

        gridPane.add(textInput,0,1);
        gridPane.add(flippedTextLabel, 1,1);

        gridPane.add(spinner,0,2);
        gridPane.add(spinnerChangesLabel,1,2);

        Scene scene = new Scene(gridPane);


        primaryStage.setWidth(275);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    @Override
    public void stop() throws Exception {
        super.stop();

        binding1.dispose();
        binding2.dispose();
        subscription.unsubscribe();
    }
}

For bugs, questions and discussions please use the Github Issues.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.