java - 如何在 javaFX 中将光标更改为 WAIT 的同时线程化后台任务？

Question

我有一个应用程序，在登录时通过接口(interface)类访问数据库。登录过程导致应用程序在访问数据库时一段时间内没有响应，因此我一直在研究线程和等待游标以使其顺利运行。我尝试通过网络上的许多示例和堆栈溢出来使用线程，但我的方法似乎不起作用，我收到 java.lang.IllegalStateException: Not on FX application thread; currentThread = Thread-4 异常，我不确定如何从这里继续。我试图做的是在后台线程运行 loginLoadEverything() 方法时将光标更改为 WAIT 模式(尽管我没有在其中包含代码，因为它太长了)。这是我的 Controller 类:

package main.java.gui;

import javafx.application.Platform;
import javafx.concurrent.Service;
import javafx.concurrent.Task;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.scene.Cursor;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.stage.Stage;
import main.java.databaseInterface.BackendInterface;
import java.net.URL;
import java.util.ResourceBundle;
import java.util.concurrent.CountDownLatch;

public class LoginController implements Initializable {


    private BackendInterface backendInterface;
    private DashboardController dashboardController;
    private StudentsController studentsController;
    private ConsultationController consultationController;
    private CreateStudentController createStudentController;
    private CreateConsultationController createConsultationController;

    @FXML
    TextField username;

    @FXML
    PasswordField password;

    @FXML
    Button loginButton;

    @FXML
    Label loginLabel;

    @FXML
    public void loginButtonPress(ActionEvent event) {

        Service<Void> service = new Service<Void>() {
            @Override
            protected Task<Void> createTask() {
                return new Task<Void>() {
                    @Override
                    protected Void call() throws Exception {

                        loginLoadEverything();

                        final CountDownLatch latch = new CountDownLatch(1);
                        Platform.runLater(new Runnable() {
                            @Override
                            public void run() {
                                try {

                                    Scene s1 = loginLabel.getScene();
                                    s1.setCursor(Cursor.WAIT);

                                } finally {
                                    latch.countDown();
                                }
                            }
                        });
                        latch.await();
                        return null;
                    }
                };
            }
        };
        service.start();

    }

    public void loginLoadEverything() {

         //chance to true when complete
    if (username.getText().isEmpty() == false || password.getText().isEmpty() == false) {

        loginLabel.setText("Please enter data in the fields below");

    } else {

        username.setText("-----");
        password.setText("-----");
        //initialises backend interface with username and password
        backendInterface = new BackendInterface(username.getText(), password.getText().toCharArray());

        // Open a connection to the database

        if (backendInterface.openConnection()) {

            //return and print response
            System.out.println(backendInterface.getConnectionResponse());

            //directs the user to the dashboard after successful login
            try {
                if (backendInterface.getAllStudents() &&
                        backendInterface.getAllConsultations() &&
                        backendInterface.getCourses() &&
                        backendInterface.getConsultationCategories() &&
                        backendInterface.getConsultationPriorities()) {


                    FXMLLoader loader1 = new FXMLLoader();
                    loader1.setLocation(getClass().getResource("/main/res/dashboard.fxml"));
                    loader1.load();
                    Parent p = loader1.getRoot();
                    Stage stage = new Stage();
                    stage.setScene(new Scene(p));
                    stage.show();

                    //set instances to the dashboard controller
                    dashboardController = loader1.getController();
                    dashboardController.setBackendInterface(backendInterface); //pass backendInterface object to controller
                    dashboardController.setDashboardController(loader1.getController()); //pass dashboard as reference

                    //load images
                    Image logoutImage = new Image(getClass().getResourceAsStream("images/logout.png"));
                    Image userImage = new Image(getClass().getResourceAsStream("images/users.png"));
                    Image calendarImage = new Image(getClass().getResourceAsStream("images/calendar.png"));
                    Image leftArrowImage = new Image(getClass().getResourceAsStream("images/leftArrow.png"));
                    Image notepadImage = new Image(getClass().getResourceAsStream("images/notepad.png"));

                    //set images
                    dashboardController.studentLabel.setGraphic(new ImageView(userImage));
                    dashboardController.logoutLabel.setGraphic(new ImageView(logoutImage));
                    dashboardController.consultationLabel.setGraphic(new ImageView(notepadImage));

    } else {
           system.out.println(backendInterface.getExceptionMessage);
    }


    @Override
    public void initialize(URL location, ResourceBundle resources) {



}

Answer 1

这里您可能不需要Service:您只需要一个Task。

call()方法是在后台线程上执行的方法。它应该执行需要很长时间才能执行的工作(即连接到数据库并从中获取数据)，并且不得执行任何 UI 工作，因为对 UI 的更改必须 在 FX 应用程序线程上进行。您收到异常的原因是您正在从后台线程创建并显示一个 Stage。

所以基本思想是让任务从数据库获取数据并返回；然后使用任务的 onSucceeded 处理程序来显示 UI，并使用任务的结果。 (onSucceeded 处理程序在 FX 应用程序线程上执行，允许您安全地修改此处的 UI。)

我不知道你的类是如何实现的，等等，但以下内容可能会起作用。重要的是，您不要在与 UI 交互的后台线程中执行任何操作。

@FXML
public void loginButtonPress(ActionEvent event) {

    if (( ! username.getText().isEmpty()) || (! password.getText().isEmpty()) ) {

        loginLabel.setText("Please enter data in the fields below");

    } else {

        // I assume you want these values before you set them to "-----", no???
        final String uName = username.getText();
        final char[] pw = password.getText().toCharArray();

        username.setText("-----");
        password.setText("-----");

        // create task for retrieving data:

        Task<BackendInterface> loadDataTask = new Task<BackendInterface>() {

            @Override
            public BackendInterface call() throws Exception {

                BackendInterface backendInterface = new BackendInterface(uName, pw);
                if (backendInterface.openConnection()) {

                    if (backendInterface.getAllStudents() &&
                        backendInterface.getAllConsultations() &&
                        backendInterface.getCourses() &&
                        backendInterface.getConsultationCategories() &&
                        backendInterface.getConsultationPriorities()) {

                        return backendInterface ;
                    }
                 }

                 // maybe throw an exception here, depending on your requirements...
                 return null ;
            }

        };

        // show UI on task completion:

    loadDataTask.setOnSucceeded(e -> {

        BackendInterface backendInterface = loadDataTask.getValue();

        if (backendInterface == null) {
            // something went wrong... bail, or probably show error message...
            return ;
        }

        FXMLLoader loader1 = new FXMLLoader();
        loader1.setLocation(getClass().getResource("/main/res/dashboard.fxml"));
        Parent p = loader1.load();
        DashboardController controller = loader.getController();
        controller.setBackendInterface(backendInterface);

        Stage stage = new Stage();
        stage.setScene(new Scene(p));
        stage.show();

        // etc etc with your Images, etc (not sure why this isn't done in DashboardController though...)

        // set cursor back to default:
        loginLabel.getScene().setCursor(Cursor.DEFAULT);
    });

    loadDataTask.setOnFailed(e -> {
        // show error message or otherwise handle database exception here
    });

    // set cursor to WAIT:
    loginLabel.getScene().setCursor(Cursor.WAIT);

    // and run task in a background thread:
    Thread t = new Thread(loadDataTask);
    t.start();

}