JavaFX游戏开发：优化按键事件处理与AnimationTimer的正确实践

// 错误示例：Game类中的handleInput方法
private void handleInput() {
    ArrayList<String> input = new ArrayList<String>(); // 每次调用都创建新的空列表
    this.scene.setOnKeyPressed( // 每次调用都重新注册监听器
        new EventHandler<KeyEvent>() {
            public void handle(KeyEvent e) {
                String code = e.getCode().toString();
                if (!input.contains(code)) {
                    input.add(code);
                }
            }
    });
    this.scene.setOnKeyReleased(
        new EventHandler<KeyEvent>() {
            public void handle(KeyEvent e) {
                String code = e.getCode().toString();
                input.remove(code);
            }
    });
    System.out.println(input); // 总是打印空的或短暂的列表
}

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
import javafx.animation.AnimationTimer;
import javafx.event.EventHandler;
import javafx.scene.input.KeyEvent;
import javafx.scene.input.KeyCode; // 推荐使用KeyCode

import java.util.ArrayList;
import java.util.List; // 使用List接口

public class Main extends Application {
    private static Game game;

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

    @Override
    public void start(Stage stage) {
        game = new Game(stage);

        final long startNanoTime = System.nanoTime();
        new AnimationTimer() {
            public void handle(long currentNanoTime) {
                double t = (currentNanoTime - startNanoTime) / 1000000000.0;
                game.update(t);
                game.render();
            }
        }.start();
    }
}

class Game {
    private Stage stage;
    private Group root;
    private Scene scene;
    private Canvas canvas;
    private GraphicsContext gc;
    final static int WINDOW_WIDTH = 800;
    final static int WINDOW_HEIGHT = 600;

    // 将input列表声明为类的成员变量，用于持久化按键状态
    private List<KeyCode> input = new ArrayList<>();

    public Game(Stage stage) {
        this.stage = stage;
        this.root = new Group();
        this.scene = new Scene(this.root);
        this.canvas = new Canvas(WINDOW_WIDTH, WINDOW_HEIGHT);
        this.gc = this.canvas.getGraphicsContext2D();

        this.stage.setTitle("Pong");
        this.stage.setScene(this.scene);
        this.root.getChildren().add(this.canvas);

        // 在构造函数中一次性注册事件监听器
        this.scene.setOnKeyPressed(
            new EventHandler<KeyEvent>() {
                public void handle(KeyEvent e) {
                    KeyCode code = e.getCode(); // 直接使用KeyCode
                    if (!input.contains(code)) { // 避免重复添加
                        input.add(code);
                    }
                }
        });
        this.scene.setOnKeyReleased(
            new EventHandler<KeyEvent>() {
                public void handle(KeyEvent e) {
                    KeyCode code = e.getCode();
                    input.remove(code);
                }
        });
    }

    public void update(double time) {
        this.handleInput(); // 现在handleInput只负责处理和打印当前的input列表

        // 示例：根据按键输入执行游戏逻辑
        if (input.contains(KeyCode.W)) {
            System.out.println("W is pressed!");
            // 执行向上移动逻辑
        }
        if (input.contains(KeyCode.S)) {
            System.out.println("S is pressed!");
            // 执行向下移动逻辑
        }

        this.gc.setFill(Color.RED);
        this.gc.fillRect(0,0, WINDOW_WIDTH, WINDOW_HEIGHT);
    }

    public void render() {
        this.stage.show();
    }

    private void handleInput() {
        // 现在这里打印的是持久化的input列表，会显示当前按下的所有键
        System.out.println("Current pressed keys: " + input);
    }
}