如何在 Java (JavaFX) 中使用来自另一个 class 的 Label

Question

I need to use a Label that was created in another class in my JavaFx application

This is my code: Main Class

import javafx.application.Application;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.util.Scanner;

public class Main extends Application {
    Stage window;
    Scene scene1, scene2, scene3;
    private Scanner x;
    @Override
    public void start(Stage primaryStage) throws Exception {
        readTutor r = new readTutor();
        window = primaryStage;
        window.setTitle("Tutor Finder");
        Label labelA1 = new Label("Welcome to the best online tutor\nproviding service in the world");
        Button buttonA2 = new Button("Find a tutor!");
        Button buttonA1 = new Button("Become a tutor!");
        Button buttonB1 = new Button("Click here to go back");
        Button buttonB2 = new Button("Submit");
        Button buttonC1 = new Button("Click here to go back");
        buttonB1.setOnAction(e -> window.setScene(scene1));
        buttonC1.setOnAction(e -> window.setScene(scene1));
        buttonA1.setOnAction(e -> window.setScene(scene2));
        buttonA2.setOnAction(e -> window.setScene(scene3));
        Label labelB1 = new Label("First Name:");
        TextField textB1 = new TextField();
        Label labelB2 = new Label("Last Name:");
        TextField textB2 = new TextField();
        Label labelB3 = new Label("Subject:");
        TextField textB3 = new TextField();
        Label labelB4 = new Label("Age:");
        TextField textB4 = new TextField();
        Label labelB5 = new Label("Contact No#:");
        TextField textB5 = new TextField();
        Label labelB6 = new Label("Country: ");
        TextField textB6 = new TextField();
        VBox layout = new VBox(20);
        layout.setAlignment(Pos.CENTER);
        layout.getChildren().addAll(labelA1, buttonA1, buttonA2);
        scene1 = new Scene(layout, 300, 300);
        VBox layout2 = new VBox(20);
        layout2.getChildren().addAll(labelB1, textB1, labelB2, textB2, labelB3,
                textB3, labelB4, textB4, labelB5, textB5, labelB6, textB6, buttonB2, buttonB1);
        buttonB2.setOnAction(l -> {
            try {
                BufferedWriter bw = new BufferedWriter(
                        new FileWriter("C:\\Users\\Salman\\Desktop\\Tutor Details\\output.txt", true));
                bw.write(textB1.getText()+" ");
                bw.write(textB2.getText()+" ");
                bw.write(textB3.getText()+" ");
                bw.write(textB4.getText()+" ");
                bw.write(textB5.getText()+" ");
                bw.write(textB6.getText()+" \n");
                bw.close();
                textB1.clear();
                textB2.clear();
                textB3.clear();
                textB4.clear();
                textB5.clear();
                textB6.clear();
            } catch (Exception e) {
                return;
            }
            r.openFile();
            r.readFile();
            r.closeFile();
        });
        scene2 = new Scene(layout2, 400, 600);
        VBox layout3 = new VBox(20);
        layout3.setAlignment(Pos.CENTER);
        layout3.getChildren().addAll(buttonC1);
        scene3 = new Scene(layout3, 300, 300);
        window.setScene(scene1);
        window.show();
    }
        public static void main (String[]args){
            launch(args);
        }
}

readTutor Class

import javafx.scene.control.Label;

import java.io.*;
import java.util.*;

public class readTutor {

    private Scanner x;
    public Label tutorLabel;

    public void openFile(){

        try {
            x = new Scanner(new File("C:\\Users\\Salman\\Desktop\\Tutor Details\\output.txt"));
        }
        catch(Exception e){
            System.out.println("couldn't find file");
        }
    }

    public void readFile(){
        while(x.hasNext()){
            String a = x.next();
            String b = x.next();
            String c = x.next();
            String d = x.next();
            String e = x.next();
            String f = x.next();
            System.out.printf("%s %s %s %s %s %s\n", a, b, c, d, e, f);
            tutorLabel = new Label(a+b+c+d+e+f);
        }
    }


    public void closeFile(){
        x.close();
    }
}

What I want is to use the Label created in the readFile method in the readTutor Class, in scene3 and display that label there. But I can't figure out how to use that label from the Main class.

Answer 1

You should make an Object to store you're data or pass them to the target location.

Answer 2

There is much that is very, very wrong about the structure of code in the question. Mostly that it does all kinds of file handling and I/O on the FXAT, which will cause havoc with the GUI if there is any kind of lag with those operations.

Also, the idea of having a file handling helper class with a JavaFX screen Node in it is really not a good design. @Kleopatra's comment about using a data model is totally on point.

But in the spirit of answering the question about exposing the layout of a screen to other classes which have a legitimate reason to access it, I've made the required changes to the code so that it should work.

First, I've added a TextField and Label to the Main screen to show the results from the readTutor class. Then I've passed the TextField to readTutor in it's constructor:

import javafx.application.Application;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.util.Scanner;

public class LabelPasser extends Application {
    Stage window;
    Scene scene1, scene2, scene3;
    private Scanner x;

    @Override
    public void start(Stage primaryStage) throws Exception {
        window = primaryStage;
        window.setTitle("Tutor Finder");
        Label labelA1 = new Label("Welcome to the best online tutor\nproviding service in the world");
        Button buttonA2 = new Button("Find a tutor!");
        Button buttonA1 = new Button("Become a tutor!");
        Button buttonB1 = new Button("Click here to go back");
        Button buttonB2 = new Button("Submit");
        Button buttonC1 = new Button("Click here to go back");
        buttonB1.setOnAction(e -> window.setScene(scene1));
        buttonC1.setOnAction(e -> window.setScene(scene1));
        buttonA1.setOnAction(e -> window.setScene(scene2));
        buttonA2.setOnAction(e -> window.setScene(scene3));
        Label labelB1 = new Label("First Name:");
        TextField textB1 = new TextField();
        Label labelB2 = new Label("Last Name:");
        TextField textB2 = new TextField();
        Label labelB3 = new Label("Subject:");
        TextField textB3 = new TextField();
        Label labelB4 = new Label("Age:");
        TextField textB4 = new TextField();
        Label labelB5 = new Label("Contact No#:");
        TextField textB5 = new TextField();
        Label labelB6 = new Label("Country: ");
        TextField textB6 = new TextField();
        Label labelTutor = new Label("Tutor: ");
        TextField tutorTF = new TextField();
        VBox layout = new VBox(20);
        layout.setAlignment(Pos.CENTER);
        layout.getChildren().addAll(labelA1, buttonA1, buttonA2);
        readTutor r = new readTutor(tutorTF);
        scene1 = new Scene(layout, 300, 300);
        VBox layout2 = new VBox(20);
        layout2.getChildren()
               .addAll(labelB1,
                       textB1,
                       labelB2,
                       textB2,
                       labelB3,
                       textB3,
                       labelB4,
                       textB4,
                       labelB5,
                       textB5,
                       labelB6,
                       textB6,
                       labelTutor,
                       tutorTF,
                       buttonB2,
                       buttonB1);
        buttonB2.setOnAction(l -> {
            try {
                BufferedWriter bw = new BufferedWriter(new FileWriter("C:\\Users\\Salman\\Desktop\\Tutor Details\\output.txt", true));
                bw.write(textB1.getText() + " ");
                bw.write(textB2.getText() + " ");
                bw.write(textB3.getText() + " ");
                bw.write(textB4.getText() + " ");
                bw.write(textB5.getText() + " ");
                bw.write(textB6.getText() + " \n");
                bw.close();
                textB1.clear();
                textB2.clear();
                textB3.clear();
                textB4.clear();
                textB5.clear();
                textB6.clear();
            } catch (Exception e) {
                return;
            }
            r.openFile();
            r.readFile();
        });
        scene2 = new Scene(layout2, 400, 600);
        VBox layout3 = new VBox(20);
        layout3.setAlignment(Pos.CENTER);
        layout3.getChildren().addAll(buttonC1);
        scene3 = new Scene(layout3, 300, 300);
        window.setScene(scene1);
        window.show();
    }

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

Then I've modified readTutor such that it no longer creates a Label, but instead updates the Text property of the TextField that it received in its constructor:

import javafx.scene.control.Label;
import javafx.scene.control.TextField;

import java.io.File;
import java.util.Scanner;

public class readTutor {

    private Scanner x;
    public Label tutorLabel;
    TextField tutorTF;

    public readTutor(TextField tutorTF) {
        this.tutorTF = tutorTF;
    }

    public void openFile() {

        try {
            x = new Scanner(new File("C:\\Users\\Salman\\Desktop\\Tutor Details\\output.txt"));
        } catch (Exception e) {
            System.out.println("couldn't find file");
        }
    }

    public void readFile() {
        while (x.hasNext()) {
            String a = x.next();
            String b = x.next();
            String c = x.next();
            String d = x.next();
            String e = x.next();
            String f = x.next();
            System.out.printf("%s %s %s %s %s %s\n", a, b, c, d, e, f);
            tutorTF.setText(a + b + c + d + e + f);
        }
    }
}

It turns out that if you program the file handling the way you should, with a Task, then most of the issues about the label passing become moot. I've cleaned up the code a bit to make it easier to read, then split the file handling out into a Task:

import javafx.application.Application;
import javafx.concurrent.Task;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.util.Scanner;

public class LabelPasser extends Application {
    Stage window;
    Scene scene1, scene2, scene3;
    private Scanner x;
    private TextField textB1 = new TextField();
    private TextField textB2 = new TextField();
    private TextField textB3 = new TextField();
    private TextField textB4 = new TextField();
    private TextField textB5 = new TextField();
    private TextField textB6 = new TextField();
    private TextField tutorTF = new TextField();

    @Override
    public void start(Stage primaryStage) throws Exception {
        window = primaryStage;
        window.setTitle("Tutor Finder");
        Button buttonA2 = new Button("Find a tutor!");
        Button buttonA1 = new Button("Become a tutor!");
        Button buttonB1 = new Button("Click here to go back");
        Button buttonB2 = new Button("Submit");
        Button buttonC1 = new Button("Click here to go back");
        buttonB1.setOnAction(e -> window.setScene(scene1));
        buttonC1.setOnAction(e -> window.setScene(scene1));
        buttonA1.setOnAction(e -> window.setScene(scene2));
        buttonA2.setOnAction(e -> window.setScene(scene3));
        VBox layout = new VBox(20, new Label("Welcome to the best online tutor\nproviding service in the world"), buttonA1, buttonA2);
        layout.setAlignment(Pos.CENTER);
        scene1 = new Scene(layout, 300, 300);
        VBox layout2 = new VBox(20);
        layout2.getChildren()
               .addAll(new Label("First Name:"),
                       textB1,
                       new Label("Last Name:"),
                       textB2,
                       new Label("Subject:"),
                       textB3,
                       new Label("Age:"),
                       textB4,
                       new Label("Contact No#:"),
                       textB5,
                       new Label("Country: "),
                       textB6,
                       new Label("Tutor: "),
                       tutorTF,
                       buttonB2,
                       buttonB1);
        buttonB2.setOnAction(evt -> buttonAction());
        scene2 = new Scene(layout2, 400, 600);
        VBox layout3 = new VBox(20);
        layout3.setAlignment(Pos.CENTER);
        layout3.getChildren().addAll(buttonC1);
        scene3 = new Scene(layout3, 300, 300);
        window.setScene(scene1);
        window.show();
    }

    private void buttonAction() {
        Task<String> fileTask = new Task<String>() {
            @Override
            protected String call() throws Exception {
                try {
                    BufferedWriter bw = new BufferedWriter(new FileWriter("C:\\Users\\Salman\\Desktop\\Tutor Details\\output.txt", true));
                    bw.write(textB1.getText() + " ");
                    bw.write(textB2.getText() + " ");
                    bw.write(textB3.getText() + " ");
                    bw.write(textB4.getText() + " ");
                    bw.write(textB5.getText() + " ");
                    bw.write(textB6.getText() + " \n");
                    bw.close();
                    textB1.clear();
                    textB2.clear();
                    textB3.clear();
                    textB4.clear();
                    textB5.clear();
                    textB6.clear();
                } catch (Exception e) {
                    return "";
                }
                ReadTutor readTutor = new ReadTutor();
                readTutor.openFile();
                return readTutor.readFile();
            }
        };
        fileTask.setOnSucceeded(evt -> tutorTF.setText(fileTask.getValue()));
        Thread fileThread = new Thread(fileTask);
        fileThread.start();
    }


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

The readFile() method in ReadTutor was strange, and it looked like it was trying to create Labels in a loop, so the file reading is weird. I modified it just so that it would compile:

import java.io.File;
import java.util.Scanner;

public class ReadTutor {

    private Scanner x;

    public void openFile() {

        try {
            x = new Scanner(new File("C:\\Users\\Salman\\Desktop\\Tutor Details\\output.txt"));
        } catch (Exception e) {
            System.out.println("couldn't find file");
        }
    }

    public String readFile() {
        String results = "";
        while (x.hasNext()) {
            String a = x.next();
            String b = x.next();
            String c = x.next();
            String d = x.next();
            String e = x.next();
            String f = x.next();
            System.out.printf("%s %s %s %s %s %s\n", a, b, c, d, e, f);
            results = a + b + c + d + e + f;
        }
        return results;
    }
}

So now you can see that ReadTutor is just a file handler, and it returns a plain old Java String as a result and doesn't know anything about JavaFX at all. The Task handles the activity on a background thread and returns the String value from the read operation. When the Task completes, it will trigger the OnSucceeded event, which will update the value in the tutorTF TextField on the FXAT.