等待任務完成而不會阻塞javafx中的UI

Question

我正在嘗試使用JavaFX創建測驗應用程序，因為我正在使用調用問題

Q1.invoke();
Q2.invoke();

這些問題將顯示在UI線程上

public void display(McqQuestion mcqQuestion) {
        resourceAsStream  = getClass().getResourceAsStream("/mcqview.fxml");
        fxmlLoader = new FXMLLoader();
        if (executorService==null) executorService =Executors.newSingleThreadExecutor();
        Parent root = null;
        try {
            root = fxmlLoader.load(resourceAsStream);
            Mcqview controller = fxmlLoader.getController();
            controller.setAnswer1(mcqQuestion.getAnswers().get(0));
            //controller class has setters to accept question properties.
            controller.multipleChoiceQuestionType = this;
            this.view.getBorderPane().setCenter(root);
}

顯示問題后，我需要等待直到得到答案為止，如果沒有得到答案，則應該調用下一個問題。因此，我在display方法內引入了一個線程來等待超時

submit = executorService.submit(() -> {
             try {
                    TimeUnit.SECONDS.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
             });

            try {
                submit.get(20,TimeUnit.SECONDS);
                System.out.println("waiting finished");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

從future.get(); 是一個阻塞調用，它也阻塞了UI線程，如何在不阻塞UI線程的情況下實現這一目標。

Answer 1

為此，請勿使用單獨的線程。 這只會使事情變得更困難。 JavaFX提供了無需等待並發問題的等待方式。

在這種情況下，可以從帶有onFinished處理函數的PauseTransition中進行onFinished 。 處理來自事件處理程序的用戶輸入答案。

private static class Question {

    private final String questionText;
    private final String answers[];
    private final int correctAnswerIndex;

    public Question(String questionText, String[] answers, int correctAnswerIndex) {
        if (answers.length != 3) {
            // for simplicity's sake allow only exactly 3 answers
            throw new IllegalArgumentException();
        }
        this.questionText = questionText;
        this.answers = answers;
        this.correctAnswerIndex = correctAnswerIndex;
    }

}

private VBox questionPane;
private Label questionText;
private Button[] answerButtons;
private PauseTransition pauseTransition;
private Question currentQuestion;

private void answer(int index) {
    pauseTransition.stop(); // no longer wait for timeout
    Alert alert = new Alert(Alert.AlertType.INFORMATION);
    alert.setContentText((index == currentQuestion.correctAnswerIndex)
            ? "correct answer"
            : "incorrect answer");

    // show result and exit
    alert.showAndWait();
    Platform.exit();
}

private void ask(Question question) {
    questionText.setText(question.questionText);
    for (int i = 0; i < 3; i++) {
        answerButtons[i].setText(question.answers[i]);
    }
    currentQuestion = question;
    pauseTransition.playFromStart(); // start timeout timer
}

private void timeout() {
    pauseTransition.stop();
    Alert alert = new Alert(Alert.AlertType.INFORMATION);
    alert.setContentText("your time ran out");

    // cannot use showAndWait form animation directly
    Platform.runLater(() -> {
        // show result and exit
        alert.showAndWait();
        Platform.exit();
    });
}

@Override
public void start(Stage stage) {
    pauseTransition = new PauseTransition(Duration.seconds(10));
    pauseTransition.setOnFinished(evt -> timeout());

    questionText = new Label();
    questionText.setWrapText(true);

    questionPane = new VBox(questionText);
    questionPane.setPrefSize(400, 400);
    answerButtons = new Button[3];

    for (int i = 0; i < 3; i++) {
        final int answerIndex = i;
        Button button = new Button();
        button.setOnAction(evt -> answer(answerIndex));
        answerButtons[i] = button;
        questionPane.getChildren().add(button);
    }

    Scene scene = new Scene(questionPane);

    stage.setScene(scene);
    stage.show();

    Question question = new Question(
            "What is the answer to the ultimate question of life, the universe, and everything?",
            new String[]{"Mew", "42", "Peanut butter"},
            1
    );
    ask(question);
}

您可以輕松地以不同的方式實現超時或回答問題的結果，例如，提出下一個問題或在完成最后一個問題時顯示結果。

Answer 2

對於UI更改，您應該使用

Platform.runLater(() -> {

});

對於線程，您應該使用：

Task<Void> task = new Task<Void>() {
    @Override
    protected Void call() throws Exception {
                return null;
        }
};

並將任務對象傳遞給

executorService.submit(task)

希望對您有所幫助