How to update the value of Event handler in thread? - javafx

Question

I'd like to update the value of text in thread(ScheduledService) when I push the button. I can update the value of text in GUI but the value isn't capable of updating it in thread(ScheduledService).
How should I do to update the value of text in thread(ScheduledService) area?
[Procesure]
(1)when I input the value of text and push the button,the value is shown in GUI
by the following code(in EventHandler)
label.setText(text);
Value = Integer.parseInt( text);
(2)I want to pass the value of "Value" to thread by the following
recieve(Value);
(3) the value of "Value" is shown by the following code
System.out.println(a);
But , the value of "Value" is not update .it is still "0".
the value of "0" is the initial value of "Value".
public Integer Value = 0;
My Code is the following:
package javafxapplication16;
import java.io.IOException;
import javafx.application.Application;
import javafx.concurrent.ScheduledService;
import javafx.concurrent.Task;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.ButtonBuilder;
import javafx.scene.control.Label;
import javafx.scene.control.LabelBuilder;
import javafx.scene.control.TextField;
import javafx.scene.control.TextFieldBuilder;
import javafx.scene.layout.HBox;
import javafx.scene.layout.HBoxBuilder;
import javafx.scene.text.Font;
import javafx.scene.text.FontPosture;
import javafx.stage.Stage;
import javafx.stage.StageBuilder;
public class JavaFXApplication16 extends Application {
public Label label;
public Integer Value = 0;
public Button bt_co;
public TextField tx;
#Override
public void start(Stage stage) throws Exception{
tx = TextFieldBuilder.create().text("").build();
Font font = Font.font("Arial",FontPosture.ITALIC,20);
label = LabelBuilder.create().text("value")
.alignment(Pos.CENTER)
.font(font)
.prefWidth(200).build();
bt_co = ButtonBuilder.create().text("")
.prefWidth(200)
.alignment(Pos.CENTER)
.id("")
.build();
HBox root = HBoxBuilder.create().spacing(100).children(tx,label,bt_co).build();
Scene scene = new Scene(root);
scene.addEventHandler(ActionEvent.ACTION,actionHandler);
recieve(Value); // pass the value of "Value" to thread
stage = StageBuilder.create().width(640).height(640).scene(scene).title(" ").build();
stage.show();
}
/* thread */
private void recieve(int a ) throws IOException {
ScheduledService<Boolean> ss = new ScheduledService<Boolean>()
{
#Override
protected Task<Boolean> createTask()
{
Task<Boolean> task = new Task<Boolean>()
{
#Override
protected Boolean call() throws Exception
{
System.out.println(a);
return true;
};
};
return task;
}
};
ss.start();
}
/* Event Handler */
EventHandler<ActionEvent> actionHandler = new EventHandler<ActionEvent>(){
public void handle (ActionEvent e){
Button src =(Button)e.getTarget();
String text = tx.getText();
label.setText(text);
Value = Integer.parseInt( text);
}
};
public static void main(String[] args) {
launch(args);
}
}

Answer 1

Parameter values are evaluated right before the method is invoked. It's that value that is passed, not some value that may be written to some field involved in the expression used as function parameter.
This means what happens is
UI is build.
Event handler is added
receive is executed and the value currently stored in the Value field is passed as parameter, which is 0 at this time.
(ScheduledService prints 0 repeatedly)
At some time the event handler is executed writing a new value to the Value field
(ScheduledService continues printing 0, since this is the value of a)
For any different behavior you'd need to use a expression inside the task that actually changes it's value, e.g.
volatile Integer Value;
...
receive();
...
private void recieve() /* throws IOException */ {
ScheduledService<Boolean> ss = new ScheduledService<Boolean>()
{
#Override
protected Task<Boolean> createTask()
{
Task<Boolean> task = new Task<Boolean>()
{
#Override
protected Boolean call() throws Exception
{
System.out.println(a);
return true;
};
};
return task;
}
};
ss.start();
}
BTW: You should get rid of those uses of builders. They are all deprecated in JavaFX 8, not even documented in the javadocs and will probably be removed in JavaFX 9.