Binding a JavaFX variable to a Java class instance variable

Question

Hi,
I am pretty new to JavaFX but have been developing in Java for many years. I am trying to develop a JavaFX webservice client. What I am doing is creating a basic scene that displays the data values that I am polling with a Java class that extends Thread. The Java class is reading temperature and voltage from a remote server and storing the response in an instance variable. I would like to bind a JavaFx variable to the Java class instance variable so that I can display the values whenever they change.
var conn: WebserviceConnection; // Java class that extends Thread
var response: WebserviceResponse;
try {
conn = new WebserviceConnection("some_url");
conn.start();
Thread.sleep(10000);
} catch (e:Exception) {
e.printStackTrace();
def bindTemp = bind conn.getResponse().getTemperature();
def bindVolt = bind conn.getResponse().getVoltage();
The WebserviceConnection class is opening a socket connection and reading some data in a separate thread. A regular socket connection is used because the server is not using HTTP.
When I run the application, the bindTemp and bindVolt are not updated whenever new data values are received.
Am I missing something with how bind works? Can I do what I want to do with 'bind'. I basically want to run a separate thread to retrieve data and want my UI to be updated when the data changes.
Is there a better way to do this than the way I am trying to do it?
Thanks for any help in advance.
-Richard

Answer 1

Hi,
If you don't want to constantly poll for value change, you can use the observer design pattern, but you need to modify the classes that serve the values to javafx.
Heres a simple example:
The Thread which updates a value in every second:
// TimeServer.java
public class TimeServer extends Thread {
    private boolean interrupted = false;
    public ValueObject valueObject = new ValueObject();
    @Override
    public void run() {
        while (!interrupted) {
            try {
                valueObject.setValue(Long.toString(System.currentTimeMillis()));
                sleep(1000);
            } catch (InterruptedException ex) {
                interrupted = true;
}The ValueObject class which contains the values we want to bind in javafx:
// ValueObject.java
import java.util.Observable;
public class ValueObject extends Observable {
    private String value;
    public String getValue() {
        return this.value;
    public void setValue(String value) {
        this.value = value;
        fireNotify();
    private void fireNotify() {
        setChanged();
        notifyObservers();
}We also need an adapter class in JFX so we can use bind:
// ValueObjectAdapter.fx
import java.util.Observer;
import java.util.Observable;
public class ValueObjectAdapter extends Observer {
    public-read var value : String;
    public var valueObject : ValueObject
        on replace { valueObject.addObserver(this)}
    override function update(observable: Observable, arg: Object) {
         // We need to run every code in the JFX EDT
         // do not change if the update method can be called outside the Event Dispatch Thread!
         FX.deferAction(
             function(): Void {
                value = valueObject.getValue();
}And finally the main JFX code which displays the canging value:
// Main.fx
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.text.Text;
import javafx.scene.text.Font;
import threadbindfx.TimeServer;
var timeServer : TimeServer;
var valueObjectAdapter : ValueObjectAdapter = new ValueObjectAdapter();
timeServer = new TimeServer();
valueObjectAdapter.valueObject = timeServer.valueObject;
timeServer.start();
Stage {
    title: "Time Application"
    width: 250
    height: 80
    scene: Scene {
        content: Text {
            font : Font {
                size : 24
            x : 10, y : 30
            content: bind valueObjectAdapter.value;
}This approach uses less cpu time than constant polling, and changes aren't dependent on the polling interval.
However this cannot be applied to code which you cannot change obviously.
I hope this helps.