为什么将我的点添加到场景时看不到任何点？

Question

我已经为 java fx 创建了一个程序来输入数组中的点。这些点将用在最大点之间绘制的线来显示。此外，如果您单击鼠标左键，它会添加一个点并重新计算最大点。如果右键单击，则会从显示中删除该点。我遇到的问题是我正在读取带有点的文件，但显示屏上没有显示任何内容。我什至尝试手动添加点，但显示屏上仍然没有显示任何内容。我错过了什么？

我已尽我所能来理解为什么没有显示任何点并且不知所措。我知道这很简单，但我无法弄清楚。 应从文本文件添加的点是 这是最初运行时的样子 这就是它实际的样子 我已经更正了鼠标事件，因此如果我单击左上角，它将添加点

Point.java

package application;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

public final class Point implements Comparable<Point> {
    private final double x;
    private final double y;

    public Point(double x, double y) {
        this.x = x;
        this.y = y;
    }

    public double getX() {
        return x;
    }

    public double getY() {
        return y;
    }

    public boolean isBelowAndLeftOf(Point other) {
        return this.x <= other.getX() && this.y <= other.getY();
    }

    @Override
    public int compareTo(Point other) {
        return Double.compare(this.x, other.getX());
    }
}

MaximalPointsPane.java

package application;

import javafx.scene.input.MouseEvent;
import javafx.scene.layout.Pane;
import javafx.scene.shape.Line;
import javafx.scene.input.MouseButton;
import java.util.Collections;
import java.util.ArrayList;

public class MaximalPointsPane extends Pane {
    private final ArrayList<Point> points;
    private final ArrayList<Point> maximalPoints;

    public MaximalPointsPane(ArrayList<Point> points) {
        this.points = points;
        this.maximalPoints = new ArrayList<>();
        findMaximalPoints();
        drawMaximalLines();
        this.setOnMouseClicked(this::handleMouseClick);
    }

    private void findMaximalPoints() {
        maximalPoints.clear();
        for (Point p1 : points) {
            boolean isMaximal = true;
            for (Point p2 : points) {
                if (p1 != p2 && p2.isBelowAndLeftOf(p1)) {
                    isMaximal = false;
                    break;
                }
            }
            if (isMaximal) {
                maximalPoints.add(p1);
            }
        }
    }

    private void drawMaximalLines() {
        getChildren().clear();
        for (int i = 0; i < maximalPoints.size() - 1; i++) {
            Point p1 = maximalPoints.get(i);
            Point p2 = maximalPoints.get(i + 1);
            Line line = new Line(p1.getX(), p1.getY(), p2.getX(), p2.getY());
            getChildren().add(line);
        }
    }

    private void handleMouseClick(MouseEvent event) {
        if (event.isPrimaryButtonDown()) {
            // Left click
            double x = event.getX();
            double y = event.getY();
            points.add(new Point(x, y));
            findMaximalPoints();
            drawMaximalLines();
        } else if (event.isSecondaryButtonDown()) {
            // Right click
            double x = event.getX();
            double y = event.getY();
            Point pointToRemove = null;
            for (Point p : points) {
                if (Math.abs(p.getX() - x) < 5 && Math.abs(p.getY() - y) < 5) {
                    pointToRemove = p;
                    break;
                }
            }
            if (pointToRemove != null) {
                points.remove(pointToRemove);
                findMaximalPoints();
                drawMaximalLines();
            }
        }
    }
}

Main.java

package application;

import javafx.application.Application;

import javafx.scene.Scene;
import javafx.stage.Stage;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;

public class Main extends Application {
    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage stage) {
        ArrayList<Point> points = new ArrayList<>();
        try {
            File file = new File("points.txt");
            Scanner scanner = new Scanner(file);
            while (scanner.hasNext()) {
                double x = scanner.nextDouble();
                double y = scanner.nextDouble();
                points.add(new Point(x, y));
            }
            scanner.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
            
        }
       
        
        MaximalPointsPane pane = new MaximalPointsPane(points);
        Scene scene = new Scene(pane, 500, 500);
        stage.setTitle("Maximal Points");
        stage.setScene(scene);
        stage.show();
    }
}

Answer 1

方法

isPrimaryButtonDown()

（还有

isSecondaryButtonDown()

）是这里使用的错误方法。请参阅文档。

基本上，按下并释放鼠标按钮时会发生鼠标单击。由于鼠标单击事件发生在释放之后，因此此时不会按下鼠标按钮。

而是使用

if (event.getButton() == MouseButton.PRIMARY)

等：

    private void handleMouseClick(MouseEvent event) {
        if (event.getButton() == MouseButton.PRIMARY) {
            // Left click
            double x = event.getX();
            double y = event.getY();
            points.add(new Point(x, y));
            findMaximalPoints();
            drawMaximalLines();
        } else if (event.getButton() == MouseButton.SECONDARY) {
            // Right click
            double x = event.getX();
            double y = event.getY();
            Point pointToRemove = null;
            for (Point p : points) {
                if (Math.abs(p.getX() - x) < 5 && Math.abs(p.getY() - y) < 5) {
                    pointToRemove = p;
                    break;
                }
            }
            if (pointToRemove != null) {
                points.remove(pointToRemove);
                findMaximalPoints();
                drawMaximalLines();
            }
        }
    }

或者，等效地，使用 switch 语句：

    private void handleMouseClick(MouseEvent event) {
        switch (event.getButton()) {
            case PRIMARY -> {
                // Left click
                double x = event.getX();
                double y = event.getY();
                points.add(new Point(x, y));
                findMaximalPoints();
                drawMaximalLines();                
            }
            case SECONDARY -> {
                // Right click
                double x = event.getX();
                double y = event.getY();
                Point pointToRemove = null;
                for (Point p : points) {
                    if (Math.abs(p.getX() - x) < 5 && Math.abs(p.getY() - y) < 5) {
                        pointToRemove = p;
                        break;
                    }
                }
                if (pointToRemove != null) {
                    points.remove(pointToRemove);
                    findMaximalPoints();
                    drawMaximalLines();
                }
            }
        }
    }

我不相信你计算“最大点”的逻辑。由于您没有提供“最大点”的定义或测试文件，因此无法说明为什么您没有从文件中看到任何点。上述更改在单击窗格后在某些情况下确实会显示一些点和线。