Add elements on TextFlow using external Thread in JavaFX

Question

My program sends a message to the server which is shown in a window and receives a message from a window which is also added in the window of client.

But my program doesn't show the message received from the server though i added:

textFlow.getChildren().add(text); in accept thread.

What should i do?

public class NewClient extends Application {

Thread send;
Thread accept;

DatagramPacket pack;
DatagramSocket sock;
private List<String> str;
String name , sname;
int listeningPort;
InetAddress server_ip;

String sender;
ScrollPane sp = new ScrollPane();
TextFlow textFlow = new TextFlow();
TextField userTextField = new TextField();
TextField fTextField = new TextField();

private String message;
private String recip = null;
Button button = new Button("Send");

volatile boolean st = false;
Stage theStage;

public Scene Chat_Box() {

    TextFlow textFlow = new TextFlow();
    textFlow.setPadding(new Insets(10));
    textFlow.setLineSpacing(10);
    TextField textField = new TextField();
    textField.setPrefSize(50, 30);
    Button button = new Button("Send");
    button.setPrefSize(80, 30);
    VBox container = new VBox();
    VBox box = new VBox();
    box.getChildren().addAll(sp, textFlow);
    container.setPadding(new Insets(10));
    container.getChildren().addAll(box, new HBox(textField, button));
    VBox.setVgrow(sp, Priority.ALWAYS);
    VBox.setVgrow(textFlow, Priority.ALWAYS);

    textField.prefWidthProperty().bind(container.widthProperty().subtract(button.prefWidthProperty()));

    textField.setOnKeyPressed(e -> {
        if (e.getCode() == KeyCode.ENTER) {
            button.fire();
        }
    });
    button.setOnAction(e -> {
        st = true;
        Text text;
        if (textFlow.getChildren().size() == 0) {
            text = new Text(textField.getText());
            message = textField.getText();
            System.out.println(message);
        } else {
            message = textField.getText();
            text = new Text("\n" + textField.getText());
        }
        if (textField.getText().contains(":)")) {
            ImageView imageView = new ImageView(
                    "http://files.softicons.com/download/web-icons/network-and-security-icons-by-artistsvalley/png/32x32/Regular/Friend%20Smiley.png");
            // Remove :) from text
            text.setText(text.getText().replace(":)", " "));
            textFlow.getChildren().addAll(text, imageView);
        } else {
            textFlow.getChildren().add(text);
        }
        textField.clear();
        textField.requestFocus();
    });
    VBox vb = new VBox();
    vb.getChildren().addAll(textFlow);
    sp.setVmax(440);
    sp.setPrefSize(400, 300);
    sp.setContent(vb);
    sp.vvalueProperty().bind((ObservableValue<? extends Number>) vb.heightProperty());
    Scene scene2 = new Scene(container, 400, 300);
    return scene2;
}

public void start(Stage stage) throws IOException {
    this.str = getParameters().getRaw();
    name = str.get(0);
    listeningPort = Integer.parseInt(str.get(1));
    server_ip = InetAddress.getByName(str.get(2));
    theStage = stage;
    Scene scene = Chat_Box();
    stage.setScene(scene);
    stage.show();
    send = new Thread() {

        public void run() {
            DatagramSocket sock = null;
            try {
                sock = new DatagramSocket();
            } catch (SocketException ex) {
                Logger.getLogger(NewClient.class.getName()).log(Level.SEVERE, null, ex);
            }
            while (true) {
                InetAddress host = server_ip;
                try {
                    if (st && ( message != null )) {
                        String in = message;
                        byte[] data = new byte[1024];
                        data = in.getBytes();
                        DatagramPacket sendPack = new DatagramPacket(data, data.length);
                        sendPack.setPort(5050);
                        sendPack.setAddress(host);
                        sock.send(sendPack);
                        st = false;
                    }
                } catch (Exception e) {
                    System.out.println(e);
                }
            }
        }

    };
    send.start();
    accept = new Thread() {

        public void run() {
            try {
                sock = new DatagramSocket(listeningPort);
            } catch (SocketException e) {
                e.printStackTrace();
            }
            while (true) {
                byte[] data = new byte[1024];
                pack = new DatagramPacket(data, data.length);
                try {
                    sock.receive(pack);
                } catch (IOException e) {
                    e.printStackTrace();
                }
                String incoming = null;
                try {
                    incoming = new String(data, "UTF-8");
                } catch (UnsupportedEncodingException e) {
                    e.printStackTrace();
                }
                Text text = new Text(incoming);
                textFlow.getChildren().add(text);
            }
        }
    };
    accept.start();
}

public static void main(String[] args) throws IOException {
    launch(args);
}

}

Answer 1

You should use:

Platform.runLater(()->{

 Text text = new Text(incoming);
 textFlow.getChildren().add(text);

});

The SceneGraph is not allowed to be changed from other Threads . Only JavaFX main Thread can modify the SceneGraph.

So calling this method you send this Runnable Object to a QUEUEand it will be called from the JavaFX Main Thread to modify the SceneGraph.

---

What is the SceneGraph?

The GUI in JavaFX is constructed as a scene graph. A scene graph is a collection of visual elements,called nodes, arranged in a hierarchical fashion. A scene graph is built using the public JavaFX API.

---

How events are managed in JavaFX?

In JavaFX,event queues are managed by a single, operating system–level thread called JavaFX Application Thread. All user input events are dispatched on the JavaFX Application Thread. JavaFX requires that a live scene graph must be modified only on the JavaFX Application Thread.

---

Where should i use Platform.runLater(()->{....});

Every where you are modifying a live SceneGraph from an External Thread other than JavaFX Main Thread.

Extra Links:

How JavaFX application thread works?

Platform.runLater and Task in JavaFX