使用 javafx 创建一个从数字开始倒计时并在 0 播放音乐的程序

Question

正在尝试创建一个显示窗格的程序，用户可以在其中输入数字并按 Enter 键。

然后程序应每隔一秒从该数字开始倒计时。

一旦计数器达到 0，它应该播放声音。

我在让我的程序运行时遇到问题，并且不完全确定我在哪里搞砸了或者我做错了什么。

所以理论上，如果用户输入“30”，它应该开始倒数到 0，每次减一。 29 ... 28 ... 27 ... 等等

这是我的代码：

public class Counter extends Application {

    private static final String MEDIA_URL = "http://cs.armstrong.edu/liang/common/sample.mp4";
    private TextField text = new TextField();
    int countDown = Integer.parseInt(text.getText());

    @Override
    public void start(Stage primaryStage) {

        Media media = new Media(MEDIA_URL);
        MediaPlayer mediaPlayer = new MediaPlayer(media);


        // create a pane and add a TextField
        BorderPane pane = new BorderPane();
        pane.setCenter(text);
        text.setFont(Font.font("Times", 35));

        // create a new animation
        Timeline animation = new Timeline(
            new KeyFrame(Duration.millis(1000), e -> {
                if (countDown > 0) {
                    countDown--;
                    text.setText(Integer.toString(countDown));
                }
                else {
                    mediaPlayer.play();
                }
              }));
              animation.setCycleCount(Timeline.INDEFINITE);

        // create and register a handler
        text.setOnAction(e -> text.setText(text.getText()));
        text.setOnAction(e -> animation.play());

        // create a scene and place it in the stage
        Scene scene = new Scene(pane);
        primaryStage.setScene(scene);
        primaryStage.show();

    }

    public static void main(String args[]) {

        Application.launch(args);

    }

}

编辑：在运行之后，我得到了这一长串错误：

Exception in Application constructor
java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(Unknown Source)
    at com.sun.javafx.application.LauncherImpl.launchApplication(Unknown Source)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at sun.launcher.LauncherHelper$FXHelper.main(Unknown Source)
Caused by: java.lang.RuntimeException: Unable to construct Application instance: class Counter
    at com.sun.javafx.application.LauncherImpl.launchApplication1(Unknown Source)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication5(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication11(Unknown Source)
    at com.sun.javafx.application.PlatformImpl.lambda$runAndWait5(Unknown Source)
    at com.sun.javafx.application.PlatformImpl.lambda$null3(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl.lambda$runLater4(Unknown Source)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null8(Unknown Source)
    ... 1 more
Caused by: java.lang.NumberFormatException: For input string: ""
    at java.lang.NumberFormatException.forInputString(Unknown Source)
    at java.lang.Integer.parseInt(Unknown Source)
    at java.lang.Integer.parseInt(Unknown Source)
    at Counter.<init>(Counter.java:18)
    ... 13 more
Exception running application Counter

Answer 1

您的代码中有几个错误：

您正在读取文本字段并立即设置 countDown，即在用户输入任何内容之前。当用户在文本字段上执行操作时，您需要阅读文本。
您将动画的循环计数设置为 INDEFINITE 而不是 countDown
您设置了一次循环计数，而不是在用户提交文本字段时设置它
您将按钮的 onAction 属性设置了两次。 onAction 只是一个属性和其他任何东西一样：如果你设置它然后再次设置它，它将只保存第二个值，即第一次调用 textField.setOnAction(...) 不会有任何效果。
文本字段上的第一个操作处理程序无论如何都不做任何事情：它将文本字段的文本设置为文本字段的当前文本。

你需要这样的东西：

import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.TextField;
import javafx.scene.layout.BorderPane;
import javafx.scene.media.Media;
import javafx.scene.media.MediaPlayer;
import javafx.scene.text.Font;
import javafx.stage.Stage;
import javafx.util.Duration;

public class Counter extends Application {

    private static final String MEDIA_URL = "http://cs.armstrong.edu/liang/common/sample.mp4";
    private TextField text = new TextField();
    int countDown;

    @Override
    public void start(Stage primaryStage) {

        Media media = new Media(MEDIA_URL);
        MediaPlayer mediaPlayer = new MediaPlayer(media);

        // create a pane and add a TextField
        BorderPane pane = new BorderPane();
        pane.setCenter(text);
        text.setFont(Font.font("Times", 35));

        // create a new animation
        Timeline animation = new Timeline(new KeyFrame(Duration.millis(1000), e -> {
            if (countDown > 0) {
                countDown--;
                text.setText(Integer.toString(countDown));
            } else {
                mediaPlayer.play();
            }
        }));

        // create and register a handler
        // text.setOnAction(e -> text.setText(text.getText()));
        text.setOnAction(e -> {
            countDown = Integer.parseInt(text.getText());
            animation.setCycleCount(countDown + 1);
            animation.play();
        });

        // create a scene and place it in the stage
        Scene scene = new Scene(pane);
        primaryStage.setScene(scene);
        primaryStage.show();

    }

    public static void main(String args[]) {

        Application.launch(args);

    }

}

您可能还应该解决许多其他问题（例如，如果用户在动画正在进行时在文本字段上执行操作会发生什么，等等）但这至少会达到 "work".

使用 javafx 创建一个从数字开始倒计时并在 0 播放音乐的程序

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