What is the best way to manage multithreading in JavaFX 8?
Solution 1
In addition to using the low-level Thread
API and Platform.runLater(...)
to schedule code to be executed on the FX Application Thread, as in Tomas' answer, another option is to use the FX concurrency API. This provides Service
and Task
classes, which are intended to be executed on background threads, along with callback methods which are guaranteed to be executed on the FX Application Thread.
For your simple example, this looks like a bit too much boilerplate code, but for real application code it is quite nice, providing a clean separation between the background task and the UI update that is performed on completion. Additionally, Task
s can be submitted to Executor
s.
import javafx.application.Application;
import javafx.concurrent.Task ;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;
public class ClassApplication extends Application {
private Pane pane;
public Parent createContent() {
/* layout */
BorderPane layout = new BorderPane();
/* layout -> center */
pane = new Pane();
pane.setMinWidth(250);
pane.setMaxWidth(250);
pane.setMinHeight(250);
pane.setMaxHeight(250);
pane.setStyle("-fx-background-color: #000000;");
/* layout -> center -> pane */
Circle circle = new Circle(125, 125, 10, Color.WHITE);
/* add items to the layout */
pane.getChildren().add(circle);
layout.setCenter(pane);
return layout;
}
@Override
public void start(Stage stage) throws Exception {
stage.setScene(new Scene(createContent()));
stage.setWidth(300);
stage.setHeight(300);
stage.show();
Task<Void> task = new Task<Void>() {
@Override
public Void call() throws Exception {
Thread.sleep(2000);
return null ;
}
};
task.setOnSucceeded(event -> {
Circle circle = new Circle(50, 50, 10, Color.RED);
pane.getChildren().setAll(circle);
});
new Thread(task).run();
}
public static void main(String args[]) {
launch(args);
}
}
If all you are doing is pausing, you can even get away with using (or abusing?) the animation API. There's a PauseTransition
that pauses for a specified time, and you can use its onFinished
handler to execute the update:
import javafx.application.Application;
import javafx.animation.PauseTransition ;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;
import javafx.util.Duration ;
public class ClassApplication extends Application {
private Pane pane;
public Parent createContent() {
/* layout */
BorderPane layout = new BorderPane();
/* layout -> center */
pane = new Pane();
pane.setMinWidth(250);
pane.setMaxWidth(250);
pane.setMinHeight(250);
pane.setMaxHeight(250);
pane.setStyle("-fx-background-color: #000000;");
/* layout -> center -> pane */
Circle circle = new Circle(125, 125, 10, Color.WHITE);
/* add items to the layout */
pane.getChildren().add(circle);
layout.setCenter(pane);
return layout;
}
@Override
public void start(Stage stage) throws Exception {
stage.setScene(new Scene(createContent()));
stage.setWidth(300);
stage.setHeight(300);
stage.show();
PauseTransition pause = new PauseTransition(Duration.millis(2000));
pause.setOnFinished(event -> pane.getChildren().setAll(new Circle(50, 50, 10, Color.RED)));
pause.play();
}
public static void main(String args[]) {
launch(args);
}
}
If you need to execute the pause multiple times, you can use a Timeline
, and call setCycleCount(...)
:
import javafx.application.Application;
import javafx.animation.Timeline ;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;
import javafx.util.Duration ;
public class ClassApplication extends Application {
private Pane pane;
public Parent createContent() {
/* layout */
BorderPane layout = new BorderPane();
/* layout -> center */
pane = new Pane();
pane.setMinWidth(250);
pane.setMaxWidth(250);
pane.setMinHeight(250);
pane.setMaxHeight(250);
pane.setStyle("-fx-background-color: #000000;");
/* layout -> center -> pane */
Circle circle = new Circle(125, 125, 10, Color.WHITE);
/* add items to the layout */
pane.getChildren().add(circle);
layout.setCenter(pane);
return layout;
}
@Override
public void start(Stage stage) throws Exception {
stage.setScene(new Scene(createContent()));
stage.setWidth(300);
stage.setHeight(300);
stage.show();
KeyFrame keyFrame = new KeyFrame(Duration.millis(2000),
event -> pane.getChildren().setAll(new Circle(50, 50, 10, Color.RED)));
Timeline timeline = new Timeline(keyFrame);
// Repeat 10 times:
timeline.setCycleCount(10);
timeline.play();
}
public static void main(String args[]) {
launch(args);
}
}
Solution 2
You can access the scene only from the JavaFX application thread. You need to wrap your code that accesses the scene graph in Platform.runLater()
:
Platform.runLater(() -> {
Circle circle = new Circle(50, 50, 10, Color.RED);
pane.getChildren().clear();
pane.getChildren().add(circle);
});
bluevoxel
Updated on July 24, 2022Comments
-
bluevoxel almost 2 years
I'm trying to find an efficient way to influence the shape and the content of the JavaFX GUI elements, such as simple
Pane
, with use of multithreading. Let's say I have a simplePane
, on which I display filledCircle
s at the given itervals of time, and I want to have the posibility to answer to them, e.g. by hitting the corresponding key. So far, for this purpose, I tried to use class with the implementation ofRunnable
interface and creation of classicThread
object in it, in order to add and/or remove elements from the external JavaFXPane
, which was passed to that "thread class" in its constructor parameter from the mainApplication
class. Say, both classes, 1) application and 2) thread class, looks like this:import javafx.application.Application; import javafx.scene.Parent; import javafx.scene.Scene; import javafx.scene.layout.BorderPane; import javafx.scene.layout.Pane; import javafx.scene.paint.Color; import javafx.scene.shape.Circle; import javafx.stage.Stage; public class ClassApplication extends Application { private Pane pane; public Parent createContent() { /* layout */ BorderPane layout = new BorderPane(); /* layout -> center */ pane = new Pane(); pane.setMinWidth(250); pane.setMaxWidth(250); pane.setMinHeight(250); pane.setMaxHeight(250); pane.setStyle("-fx-background-color: #000000;"); /* layout -> center -> pane */ Circle circle = new Circle(125, 125, 10, Color.WHITE); /* add items to the layout */ pane.getChildren().add(circle); layout.setCenter(pane); return layout; } @Override public void start(Stage stage) throws Exception { stage.setScene(new Scene(createContent())); stage.setWidth(300); stage.setHeight(300); stage.show(); /* initialize custom Thread */ ClassThread thread = new ClassThread(pane); thread.execute(); } public static void main(String args[]) { launch(args); } }
...and the "thread class"
import javafx.scene.layout.Pane; import javafx.scene.paint.Color; import javafx.scene.shape.Circle; public class ClassThread implements Runnable { private Thread t; private Pane pane; ClassThread(Pane p) { this.pane = p; t = new Thread(this, "Painter"); } @Override public void run() { try { Thread.sleep(2000); Circle circle = new Circle(50, 50, 10, Color.RED); pane.getChildren().clear(); pane.getChildren().add(circle); } catch (InterruptedException ie) { ie.printStackTrace(); } } public void execute() { t.start(); } }
However, such a solution, where in Swing application could be possible, in JavaFX is impossible, and what's more, is the reason of the following exception:
Exception in thread "Painter" java.lang.IllegalStateException: Not on FX application thread; currentThread = Painter at com.sun.javafx.tk.Toolkit.checkFxUserThread(Unknown Source) at com.sun.javafx.tk.quantum.QuantumToolkit.checkFxUserThread(Unknown Source) at javafx.scene.Parent$2.onProposedChange(Unknown Source) at com.sun.javafx.collections.VetoableListDecorator.clear(Unknown Source) at ClassThread.run(ClassThread.java:21) at java.lang.Thread.run(Unknown Source)
...where the line "21" is:
pane.getChildren().clear();
I've concluded, that "there is a problem with influencing the main JavaFX thread from the level of another thread". But in this case, how can I change the JavaFX GUI elements shape and content dynamically, if I can't (tbh more accurately to say will be "I don't know how") bind togheter few threads?
UPDATE : 2014/08/07, 03:42
After reading given answers I tried to implement given solutions in code, in order to display 10 custom
Circle
s on different locations with specified time intervals between each display:/* in ClassApplication body */ @Override public void start(Stage stage) throws Exception { stage.setScene(new Scene(createContent())); stage.setWidth(300); stage.setHeight(300); stage.show(); Timeline timeline = new Timeline(); for (int i = 0; i < 10; i++) { Random r = new Random(); int random = r.nextInt(200) + 25; KeyFrame f = new KeyFrame(Duration.millis((i + 1) * 1000), new EventHandler<ActionEvent>() { @Override public void handle(ActionEvent ae) { pane.getChildren().add(new Circle( random, random, 10, Color.RED)); } }); timeline.getKeyFrames().add(f); } timeline.setCycleCount(1); timeline.play(); }
The solution above works just fine. Thank you very much.
-
Tomas Mikula over 9 yearsAnd if the abuse of the animation API is still too much boilerplate, ReactFX has a wrapper around it:
FxTimer.runLater(Duration.ofMillis(2000), () -> pane.getChildren().setAll(new Circle(50, 50, 10, Color.RED)));
-
bluevoxel over 9 years@James_D The problem with this solution is that, it is good for a single delayed events. But in case of displaying multiple
Circle
s in specific intervals of time it's problematic. Say, I have 10Circle
s and I want them to be displayed one-by-one in, e.g. 2000ms intervals on the samePane
. I also tried to useTimeline
and it'sKeyValue
andKeyFrame
, but the problem is, that inKeyValue
object I can't add and remove elements from thePane
. -
James_D over 9 yearsAdded an example which repeats 10 times. You can set the cycle count to
Animation.INDEFINITE
to repeat indefinitely. And @TomasMikula no doubt has a one-liner from ReactFX for the same thing ;). -
Tomas Mikula over 9 years@James_D To repeat indefinitely, just change
runLater
in my previous comment torunPeriodically
. I don't have an easier solution for a fixed number of repetitions. I imagine something like this:EventStreams.ticks(Duration.ofMillis(2000)).limit(10).subscribe(x -> pane.getChildren().setAll(new Circle(50, 50, 10, Color.RED)))
, except thelimit
operator is not there. It's just no one has asked for it yet :) -
bluevoxel over 9 years@James_D, @Tomas Mikula, I've tried to implement your solutions in some piece of code in my question update, but I have another small problem with the multiple custom
KeyFrame
initialization, adding, and execution in theTimeline
object. The problem is, that specifiedEventHandler
s works fine, but theDuration
value is respected only for one of the addedKeyFrame
. -
Tomas Mikula over 9 years@bluevoxel In your code, you are adding 10
KeyFrame
s, all of which execute at time=1000ms. If you want to use 10 key frames instead of 10 cycles, then useDuration.millis((i+1) * 1000)
. KeyFrame's duration is paradoxically not duration of the KeyFrame, but duration since the start of the animation.