I am working on a basic Java FX task exercise. It counts from 1 to 150 on a thread. The current value is presented on a label and updates a progress bar.
There is a button to start the task, to cancel it and to view canceled status of the task.
The thing that puzzles me is as to why I cannot re run the task after having canceled the thread once(same thing happens if I let the task finnish).
I want to be able to rerun the task . Then I need to make it so that it will resume(though that shouldn't be that hard after figuring out how to rerun the task)
Source ;
public class JavaFX_Task extends Application {
#Override
public void start(Stage primaryStage) {
final Task task;
task = new Task<Void>() {
#Override
protected Void call() throws Exception {
int max = 150;
for (int i = 1; i <= max; i++) {
if (isCancelled()) {
break;
}
updateProgress(i, max);
updateMessage(String.valueOf(i));
Thread.sleep(100);
}
return null;
}
};
ProgressBar progressBar = new ProgressBar();
progressBar.setProgress(0);
progressBar.progressProperty().bind(task.progressProperty());
Label labelCount = new Label();
labelCount.textProperty().bind(task.messageProperty());
final Label labelState = new Label();
Button btnStart = new Button("Start Task");
btnStart.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent t) {
new Thread(task).start();
}
});
Button btnCancel = new Button("Cancel Task");
btnCancel.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent t) {
task.cancel();
}
});
Button btnReadTaskState = new Button("Read Task State");
btnReadTaskState.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent t) {
labelState.setText(task.getState().toString());
}
});
VBox vBox = new VBox();
vBox.setPadding(new Insets(5, 5, 5, 5));
vBox.setSpacing(5);
vBox.getChildren().addAll(
progressBar,
labelCount,
btnStart,
btnCancel,
btnReadTaskState,
labelState);
StackPane root = new StackPane();
root.getChildren().add(vBox);
Scene scene = new Scene(root, 300, 250);
primaryStage.setTitle("java-buddy.blogspot.com");
primaryStage.setScene(scene);
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}
The Task documentation is pretty clear on this.
As with FutureTask, a Task is a one-shot class and cannot be reused. See Service for a reusable Worker.
There is an example of restartable concurrent services in the Service documentation.
Related
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.
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);
}
}
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();
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();
}
});
I have this code which displays confirmation dialog to exit application.
public class DialogPanels
{
public void initClosemainAppDialog(final Stage primaryStage)
{
primaryStage.setOnCloseRequest(new EventHandler<WindowEvent>()
{
#Override
public void handle(WindowEvent event)
{
event.consume(); // Do nothing on close request
// Dialog Stage init
final Stage dialog = new Stage();
dialog.initModality(Modality.APPLICATION_MODAL);
// Frage - Label
Label label = new Label("Exit from the program");
// Button "Yes"
Button okBtn = new Button("Yes");
okBtn.setOnAction(new EventHandler<ActionEvent>()
{
#Override
public void handle(ActionEvent event)
{
//primaryStage.close();
//dialog.close();
//Platform.exit();
System.exit(0);
}
});
// Button "No"
Button cancelBtn = new Button("No");
cancelBtn.setOnAction(new EventHandler<ActionEvent>()
{
#Override
public void handle(ActionEvent event)
{
primaryStage.show();
dialog.close();
}
});
// Layout for the Button
HBox hbox = new HBox();
hbox.setSpacing(10);
hbox.setAlignment(Pos.CENTER);
hbox.getChildren().add(okBtn);
hbox.getChildren().add(cancelBtn);
// Layout for the Label and hBox
VBox vbox = new VBox();
vbox.setAlignment(Pos.CENTER);
vbox.setSpacing(10);
vbox.getChildren().add(label);
vbox.getChildren().add(hbox);
// Stage
Scene scene = new Scene(vbox);
dialog.setScene(scene);
dialog.show();
}
});
}
}
The problem is that when close the main application the dialog box is displayed and the main stage is hidden. I want to display the dialog box in front of the main stage. Can you help me to correct this?
UPDATE
I tested this code, it's working but when the dialog is displayed the mainstage is not responsible(frozen). How I an make the mainstage responsible when I display dialog?
Consume the closing event and set the owner of the stage if you do not want to see another window when the windows are minimized:
#Override
public void handle(WindowEvent event)
{
event.consume(); // Do nothing on close request
// Dialog Stage init
final Stage dialog = new Stage();
dialog.initModality(Modality.APPLICATION_MODAL);
dialog.initOwner(primaryStage);
// other stuff
}
});
You need to set the proper relationships between primaryStage and dialog stage. Here's a hint to get you going:
...
dialog.initOwner(primaryStage);
dialog.initModality(Modality.APPLICATION_MODAL);
dialog.showAndWait();
You can find more information in Oracle's JavaFX 2 JavaDocs.
More example code (edit)
I'm using setOnHiding(..) instead of setOnCloseRequest(..):
stage.setOnHiding(new AskUserIfHeReallyWantsToQuitWindowHandler(stage));
I extracted your code into a seperate event handler class and fixed the issues I mentioned (sorry, I am little short on time right now):
public class AskUserIfHeReallyWantsToQuitWindowHandler implements EventHandler<WindowEvent> {
private final Stage primaryStage;
public AskUserIfHeReallyWantsToQuitWindowHandler(final Stage primaryStage) {
Objects.requireNonNull(primaryStage);
this.primaryStage = primaryStage;
}
#Override
public void handle(final WindowEvent event) {
event.consume();
final Stage dialog = new Stage();
final Button okBtn = new Button("Yes");
okBtn.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(final ActionEvent event) {
dialog.close();
primaryStage.close();
}
});
// Button "No"
final Button cancelBtn = new Button("No");
cancelBtn.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(final ActionEvent event) {
dialog.close();
Platform.runLater(new Runnable() {
#Override
public void run() {
primaryStage.show();
}
});
}
});
// Layout for the Button
final HBox hbox = new HBox();
hbox.setSpacing(10);
hbox.setAlignment(Pos.CENTER);
hbox.getChildren().add(okBtn);
hbox.getChildren().add(cancelBtn);
// Layout for the Label and hBox
final VBox vbox = new VBox();
vbox.setAlignment(Pos.CENTER);
vbox.setSpacing(10);
vbox.getChildren().add(new Label("Do your really want to exit?"));
vbox.getChildren().add(hbox);
// Stage
final Scene scene = new Scene(vbox);
dialog.setScene(scene);
dialog.initOwner(primaryStage);
dialog.initModality(Modality.NONE);
dialog.showAndWait();
}
}