I have a simple JavaFX 2 app, with 2 buttons, saying Start and Stop. When the start button is clicked, I want to create a background thread which will do some processing and update the UI (e.g a progress bar) as it goes along. If the stop button is clicked, I want the thread to terminate.
I've tried to do this using the javafx.concurrent.Task
class which I gathered from the documentation would work fine for this. But whenever I click Start, the UI freezes/hangs rather than staying normal.
Her's the code from the main Myprogram extends Application
class for showing the buttons:
public void start(Stage primaryStage)
{
final Button btn = new Button();
btn.setText("Begin");
//This is the thread, extending javafx.concurrent.Task :
final MyProcessor handler = new MyProcessor();
btn.setOnAction(new EventHandler<ActionEvent>()
{
public void handle(ActionEvent event)
{
handler.run();
}
});
Button stop = new Button();
stop.setText("Stop");
stop.setOnAction(new EventHandler<ActionEvent>()
{
public void handle(ActionEvent event)
{
handler.cancel();
}
}
);
// Code for adding the UI controls to the stage here.
}
Here's the code of MyProcessor
class:
import javafx.concurrent.Task;
public class MyProcessor extends Task
{
@Override
protected Integer call()
{
int i = 0;
for (String symbol : feed.getSymbols() )
{
if ( isCancelled() )
{
Logger.log("Stopping!");
return i;
}
i++;
Logger.log("Doing # " + i);
//Processing code here which takes 2-3 seconds per iteration to execute
Logger.log("# " + i + ", DONE! ");
}
return i;
}
}
Pretty simple, but the UI hangs whenever I click the Start button, though the console messages continue to get displayed (Logger.log
simply does System.out.println
)
What am I doing wrong?
Task
implements Runnable
, so when you call handler.run();
you actually run the call
method in the UI Thread. That will hang the UI.
You should start the task in a background thread, either via an executor or simply by calling new Thread(handler).start();
.
This is explained (maybe not very clearly) in the javadoc or in the JavaFX concurrency tutorial.