JavaFX - Cancel Task doesn't work - multithreading

In a JavaFX application, I have a method which takes a long time on large input. I'm opening a dialog when it is loading and I'd like the user to be able to cancel/close out the dialog and the task will quit. I created a task and added its cancellation in the cancel button handling. But the cancellation doesn't happen, the task doesn't stop executing.
Task<Void> task = new Task<Void>() {
#Override
public Void call() throws Exception {
// calling a function that does heavy calculations in another class
};
task.setOnSucceeded(e -> {
startButton.setDisable(false);
});
}
new Thread(task).start();
cancelButton.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent e) {
System.out.println("Button handled");
task.cancel();
}
);
Why isn't the task getting canceled when the button clicked?

You have to check on the cancel state (see Task's Javadoc). Have a look at this MCVE:
public class Example extends Application {
#Override
public void start(Stage primaryStage) throws Exception {
Task<Void> task = new Task<Void>() {
#Override
protected Void call() throws Exception {
new AnotherClass().doHeavyCalculations(this);
return null;
}
};
Button start = new Button("Start");
start.setOnMouseClicked(event -> new Thread(task).start());
Button cancel = new Button("Cancel");
cancel.setOnMouseClicked(event -> task.cancel());
primaryStage.setScene(new Scene(new HBox(start, cancel)));
primaryStage.show();
}
private class AnotherClass {
public void doHeavyCalculations(Task<Void> task) {
while (true) {
if (task.isCancelled()) {
System.out.println("Canceling...");
break;
} else {
System.out.println("Working...");
}
}
}
}
}
Note that…
You should use Task#updateMessage(String) rather than printing to System.out, here it's just for demonstration.
Directly injecting the Task object creates a cyclic dependency. However, you can use a proxy or something else that fits your situation.

Related

Javafx Updating UI from a Thread Java 8

I interested in one interesting task. I have UI in JavaFx with another thread which updates UI. I started updates from Platform.runLater. Code:
private void startUpdateDaemon() {
updateUserStatus();
updateTable();
}
private void startUpdateDaemonTask() {
Task task = new Task<Void>() {
#Override
protected Void call() throws Exception {
while (true) {
Platform.runLater(() -> {
startUpdateDaemon();
});
Thread.sleep(1000);
}
}
};
Thread th = new Thread(task);
th.setDaemon(true);
th.start();
}
#Override
public void initialize(URL location, ResourceBundle resources) {
startUpdateDaemonTask();
}
Also I have place in another class where I updates UI:
private void startUpdateDaemonTask() {
Task task = new Task<Void>() {
#Override
protected Void call() throws Exception {
while (true) {
Platform.runLater(new Runnable() {
#Override
public void run() {
updateGameStatus();
}
});
Thread.sleep(1000);
}
}
};
Thread th = new Thread(task);
th.setDaemon(true);
th.start();
}
So, finally I have two places with call "Platform.runLater" and different methods inside.
My question is Can I create only "one" method with one time call "Platform.runLater" and send to this method different methods which will be call ?? May be I can write finish method with consumers and send to him methods 'startUpdateDaemon()' and 'updateGameStatus()'?
Thanks a lot.
You can add a Runnable parameter to your method. This parameter is given to you Platform.runLater:
private void startUpdateDaemonTask(Runnable runner) {
Task task = new Task<Void>() {
#Override
protected Void call() throws Exception {
while (true) {
Platform.runLater(runner);
Thread.sleep(1000);
}
}
};
Thread th = new Thread(task);
th.setDaemon(true);
th.start();
}
Now you can invoke this method with your method references:
startUpdateDaemonTask(this::startUpdateDaemon);
startUpdateDaemonTask(this::updateGameStatus);

Binding Properties and using them during lengthy operations

In my JavaFX Application I want to disable a couple of Buttons during a refresh of the data from a database.
I am using the disableProperty of the Buttons I want to disable.
Here is the basic JavaFX Application, modefied to illustrate my point:
public class BindLengthy extends Application {
BooleanProperty disable = new SimpleBooleanProperty(false);
#Override
public void start(Stage primaryStage) {
Button btn = new Button();
btn.setText("Say 'Hello World'");
btn.disableProperty().bind(disable);
btn.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent event) {
disable.set(true);
try {
Thread.sleep(5000);
} catch (InterruptedException ex) {
Logger.getLogger(BindLengthy.class.getName()).log(Level.SEVERE, null, ex);
}
btn.setText("Done");
}
});
//Do all the other stuff that needs to be done to launch the application
//Like adding btn to the scene and so on...
primaryStage.show();
}
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
launch(args);
}
When executed, on the click the Button stays in the "fired" mode, waits for 5 Seconds and then changes text and disables. While I want the text to change later, I want to disableProperty Change to take effect immediately!
I tried putting the lengthy operation, represented by Thread.sleep(5000) into a task and start it on a new Thread(task), but then obviously the text is changes before the Thread awakens.
I can't put the btn.setText("Done")into the Threadas it wouldn't be executed on the JavaFX-Thread(which it needs to). So I tried joining the Thread, yet that gives the same result as not putting it into an extra Thread as well.
How can I force the diableProperty to register the new value before executing my long operation?
Use a Task and use its onSucceeded handler to update the UI:
public class BindLengthy extends Application {
BooleanProperty disable = new SimpleBooleanProperty(false);
#Override
public void start(Stage primaryStage) {
Button btn = new Button();
btn.setText("Say 'Hello World'");
btn.disableProperty().bind(disable);
btn.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent event) {
disable.set(true);
Task<String> task = new Task<String>() {
#Override
public String call() throws Exception {
Thread.sleep(5000);
return "Done" ;
}
});
task.setOnFailed(e ->
Logger.getLogger(BindLengthy.class.getName())
.log(Level.SEVERE, null, task.getException()));
task.setOnSucceeded(e -> {
btn.setText(task.getValue());
disable.set(false);
});
Thread t = new Thread(task);
t.setDaemon(true);
t.start();
}
});
//Do all the other stuff that needs to be done to launch the application
//Like adding btn to the scene and so on...
primaryStage.show();
}
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
launch(args);
}
}

Concurrency in JavaFX - task is not finished

I have two tasks, one to change screen opacity, the other to perform a complex computation. I wanted the computation to begin only after the screen fading has actually changed so I wrote the following:
Task<Void> task = new Task<Void>() {
#Override
protected Void call() throws Exception {
stage.getScene().getRoot().setOpacity(0.2);
stage.show();
return null;
}
};
Task<Void> task2 = new Task<Void>() {
#Override
protected Void call() throws Exception {
// Complex computation
return null;
}
};
task.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
#Override
public void handle(WorkerStateEvent paramT) {
// this busy waiting line was added in attempt to force the
// fading before beginning second task
while (stage.getScene().getRoot().getOpacity() != 0.2) {}
stage.show();
Platform.runLater(task2);
}
});
task2.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
#Override
public void handle(WorkerStateEvent paramT) {
stage.getScene().getRoot().setOpacity(1);
stage.show();
}
});
task.run();
However, sometimes I see the computation beginning and the screen fading only after it's done. Sometimes it does work. So I think there's a threading issue here. Note: When I'm on debug mode and stop at each task it really works everytime. What can be done to force the screen fade before the second task begins?
EDIT:
As suggested, I changed the code to the following:
Task<Void> task1 = new Task<Void>() {
#Override
protected Void call() throws Exception {
// Long computation
return null;
}
};
Task<Void> task = new Task<Void>() {
#Override
protected Void call() throws Exception {
FadeTransition ft = new FadeTransition(Duration.millis(1), stage.getScene().getRoot());
ft.setFromValue(1.0);
ft.setToValue(0.1);
ft.setCycleCount(1);
//ft.setAutoReverse(true);
ft.play();
ft.setOnFinished(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent event) {
new Thread(task1).run();
}
});
return null;
}
};
task1.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
#Override
public void handle(WorkerStateEvent paramT) {
FadeTransition ft1 = new FadeTransition(new Duration(0.1), stage.getScene().getRoot());
ft1.setFromValue(0.1);
ft1.setToValue(1.0);
ft1.setCycleCount(1);
//ft.setAutoReverse(true);
ft1.play();
//stage.show();
}
});
new Thread(task).run();
Still I see the same behavior.
Replace
new Thread(task).run();
with
new Thread(task).start();

javafx background Task is not running more than once

The following is my Task initialization
final Task<Void> vt=voiceTask();
Button btn = new Button();
btn.setText("Say");
btn.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent event) {
new Thread(vt).start();
}
});
And here is the task coding
public Task<Void> voiceTask() {
return new Task<Void>(){
#Override
protected Void call() throws Exception {
HelloWorld hw=new HelloWorld();// HelloWorld is simple .java class getting voice through sphinx
updateMessage(hw.Hello());
return null;
}
};
}
Now on clicking the btn Button for the first time,the task functions normally, but on clicking for subsequent times the task is not called.
I want task to be called on every click.
Please advice me how to modify my code to do so...
See the JavaDocs.
As with FutureTask, a Task is a one-shot class and cannot be reused.
You need to create a new Task each time the button is pressed.
final Button btn = new Button();
btn.setText("Say");
btn.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent event) {
final Task<Void> vt=voiceTask();
vt.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
#Override
public void handle(WorkerStateEvent event) {
btn.setDisable(false);
}
});
btn.setDisable(true);
new Thread(vt).start();
}
});

JavaFX: How to disable a button for a specific amount of time?

I want to disable a button for a specific time in JavaFX application. Is there any option to do this? If not, is there any work around for this?
Below is my code in application. I tried Thread.sleep, but i know this is not the good way to stop the user from clicking on next button.
nextButton.setDisable(true);
final Timeline animation = new Timeline(
new KeyFrame(Duration.seconds(delayTime),
new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent actionEvent) {
nextButton.setDisable(false);
}
}));
animation.setCycleCount(1);
animation.play();
You could use the simple approach of a thread that provides the relevant GUI calls (through runLater() of course):
new Thread() {
public void run() {
Platform.runLater(new Runnable() {
public void run() {
myButton.setDisable(true);
}
}
try {
Thread.sleep(5000); //5 seconds, obviously replace with your chosen time
}
catch(InterruptedException ex) {
}
Platform.runLater(new Runnable() {
public void run() {
myButton.setDisable(false);
}
}
}
}.start();
It's perhaps not the neatest way of achieving it, but works safely.
You could also be using the Timeline:
final Button myButton = new Button("Wait for " + delayTime + " seconds.");
myButton.setDisable(true);
final Timeline animation = new Timeline(
new KeyFrame(Duration.seconds(delayTime),
new EventHandler<ActionEvent>() {
#Override public void handle(ActionEvent actionEvent) {
myButton.setDisable(false);
}
}));
animation.setCycleCount(1);
animation.play();
The method to disable a JavaFX control is:
myButton.setDisable(true);
You can implement the time logic programmatically in any way you wish, either by polling a timer or by having this method invoked in response to some event.
If you have created this button instance through FXML in SceneBuilder, then you should assign the button an fx:id so that its reference is automatically injected into your controller object during the loading of the scene graph. This will make it easier for you to work with in your controller code.
If you have created this button programmatically, then you'll already have its reference available in your code.
Or you could use a Service and bind the running property to the disableProperty of the button do you want to disable.
public void start(Stage stage) throws Exception {
VBox vbox = new VBox(10.0);
vbox.setAlignment(Pos.CENTER);
final Button button = new Button("Your Button Name");
button.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent event) {
Service<Void> service = new Service<Void>() {
#Override
protected Task<Void> createTask() {
return new Task<Void>() {
#Override
protected Void call() throws Exception {
Thread.sleep(5000);//Waiting time
return null;
}
};
}
};
button.disableProperty().bind(service.runningProperty());
service.start();
}
});
vbox.getChildren().addAll(button);
Scene scene = new Scene(vbox, 300, 300);
stage.setScene(scene);
stage.show();
}
But the Timeline solution given by Uluk Biy, looks more elegant.

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