java - 从另一个线程控制倒计时

Question

我想在我的 JavaFX 应用程序中实现一个计数器。该行为只需通过按钮进行控制:

1. 当用户首先点击按钮时，倒计时开始倒计时 10, 9, 8, ..., 0
2. 当用户在倒计时期间点击按钮时，倒计时应该取消
3. 2. 之后，用户应该能够再次从 10 开始倒计时

在倒计时期间，会处理一些繁重的数学计算(在我的应用程序音频分析中)。

如果我以正确的方式做的话，你能看一下我的源代码吗？特别是我应该在 CountdownController 或 CountdownView 中执行 Platform.runLater 操作，我可以使用简单的 Java Thread 或者我应该使用 JavaFX Service/Task 类？欢迎提出任何建议。

该应用程序分为 3 个组件:

1. CountdownTest:创建舞台并启动 JavaFX)
2. CountdownView:单例，包含一个简单的Button，将按钮事件传递给CountdownController
3. CountdownController:单例，启动一个新的Thread。在 Thread 内执行倒计时，更新 CountdownView 以显示新的倒计时状态，并处理一些数学内容。

CountdownTest.java

package org.example;

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class CountdownTest extends Application {
    @Override
    public void start(Stage primaryStage) throws Exception {
        final Group root = new Group();
        final Scene scene = new Scene(root);
        root.getChildren().setAll(CountdownView.getInstance());
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    @Override
    public void stop() throws Exception {
        super.stop();
        CountdownController.getInstance().stop();
    }

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

CountdownView.java

package org.example;

import javafx.event.EventHandler;
import javafx.scene.Group;
import javafx.scene.control.Button;
import javafx.scene.control.Tooltip;
import javafx.scene.input.MouseEvent;

public final class CountdownView extends Group {
    private static final CountdownView instance = new CountdownView();

    private Button start;

    private CountdownView() {
        start = new Button("Start");
        start.setTooltip(new Tooltip("click to start countdown"));
        start.setOnMouseClicked(new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event) {
                CountdownController.getInstance().onStartClick();
            }
        });

        this.getChildren().setAll(start);
    }

    public void startCountdown() {
        System.out.println("startCountdown");
        start.setTooltip(new Tooltip("click to stop countdown"));
    }

    public void setCountdown(final int countdown) {
        System.out.println("setCountdown " + countdown);
        start.setText(String.valueOf(countdown));
    }

    public void reset() {
        System.out.println("reset");
        start.setText("Start");
        start.setTooltip(new Tooltip("click to start countdown"));
    }

    public static CountdownView getInstance() {
        return instance;
    }
}

CountdownController.java

package org.example;

import javafx.application.Platform;

public final class CountdownController {
    private static final CountdownController instance = new CountdownController();

    private Thread countdownThread;
    private volatile boolean running = false;

    public void onStartClick() {
        if (!running) {
            countdownThread = new Thread(new Runnable() {
                @Override
                public void run() {
                    running = true;
                    int countdown = 10;
                    Platform.runLater(new Runnable() {
                        @Override
                        public void run() {
                            CountdownView.getInstance().startCountdown();
                            CountdownView.getInstance().setCountdown(10);
                        }
                    });
                    final long start = System.currentTimeMillis();
                    int lastCountdown = countdown;
                    while (!Thread.interrupted() && countdown > 0) {
                        countdown = (int) (10 - (System.currentTimeMillis() - start) / 1000);
                        if (countdown != lastCountdown) {
                            lastCountdown = countdown;
                            final int currentCountdown = countdown;
                            Platform.runLater(new Runnable() {
                                @Override
                                public void run() {
                                    CountdownView.getInstance().setCountdown(
                                            currentCountdown);
                                }
                            });
                        }

                        // Do some heavy computing stuff
                        for (int i = 0; i < 10000000; i++) {
                            Math.sin(Math.random());
                        }
                    }
                    running = false;
                    Platform.runLater(new Runnable() {
                        @Override
                        public void run() {
                            CountdownView.getInstance().reset();
                        }
                    });
                }
            });
            countdownThread.start();
        } else {
            countdownThread.interrupt();
        }
    }

    public void stop() {
        if (countdownThread != null) {
            System.out.println("stop");
            countdownThread.interrupt();
        }
    }

    public static CountdownController getInstance() {
        return instance;
    }
}

Answer 1

别出太多汗。任务和服务类只是在执行器上构建的一些实用程序，如果您不需要它们提供的功能，那么这只是额外的工作。

我认为您使用 Controller 来决定应该在哪个线程上运行是正确的，您的 View 足以在组件和 Controller 之间路由消息。