删除 java 个图形中的绘制线

Question

我有一个列表，其中包含我在 gui 上绘制的线条。我希望能够 select 一行并通过单击该行将其删除。我可以 select 并删除，但问题是重绘方法会在我这样做时擦除所有绘制的线条。当我开始绘制新线时，减去先前删除的线的线重新出现。

我觉得可能是因为迭代器，但我不完全确定。任何人都可以帮助解决这个问题吗？还是我做错了？

这是我的代码：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.RenderingHints;
import java.awt.Shape;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.awt.geom.Line2D;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class LinesDemo extends JPanel {

private List<Line2D> linesList = new ArrayList<>();
private List<Line2D> lineCollection = new ArrayList<>();
private Line2D line = null;
Point pointStart = null;
Point pointEnd   = null;
// Width and height of rectangular region around mouse
// pointer to use for hit detection on lines
private static final int HIT_BOX_SIZE = 4;

/**
 * Create the panel.
 */
public LinesDemo() {

    addMouseListener(new MouseAdapter() {
        @Override
        public void mousePressed(MouseEvent e) {
            pointStart = e.getPoint();
            line = new Line2D.Double(e.getPoint(), e.getPoint());
            linesList.add(line);
        }

        @Override
        public void mouseReleased(MouseEvent e) {
            pointStart = null;
        }

        @Override
        public void mouseClicked(MouseEvent e) {
            int x = e.getX();
            int y = e.getY();
            getClickedLine(x, y);
        }
    });

    addMouseMotionListener(new MouseMotionAdapter() {
        @Override
        public void mouseMoved(MouseEvent e) {
            pointEnd = e.getPoint();
        }

        @Override
        public void mouseDragged(MouseEvent e) {
            pointEnd = e.getPoint();
            line.setLine(pointStart, pointEnd);
            lineCollection.add(line);
            repaint();
        }
    });
}

private Shape getClickedLine(int x, int y) {

    int boxX = x - HIT_BOX_SIZE / 2;
    int boxY = y - HIT_BOX_SIZE / 2;

    int width = HIT_BOX_SIZE;
    int height = HIT_BOX_SIZE;

    for(Line2D selectedLine:lineCollection) {
        if (selectedLine.intersects(boxX, boxY, width, height)) {
            System.out.println("intersects!");
            removeLine(selectedLine);
            return selectedLine;
        }
    }
    return null;
}

private void removeLine(Line2D line) {
    Iterator<Line2D> it = lineCollection.iterator();
    while(it.hasNext()) {
        Line2D selectedLine = it.next();
        if(selectedLine.equals(line)) {
            it.remove();
            repaint();
        }
    }
}

@Override
public void paintComponent(Graphics g){
    super.paintComponent(g);
    Graphics2D g2d = (Graphics2D) g;
    if(pointStart != null) {
        g2d.setPaint(Color.RED);
        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        for(Shape content : lineCollection){
            g2d.draw(content);
        }
        g2d.dispose();

    }
}

@Override
public Dimension getPreferredSize() {
    return new Dimension(300, 300);
}

public static void main(String[] args) {
    JFrame frame = new JFrame("Moving and Scaling");
    LinesDemo m = new LinesDemo();
    frame.add(m);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(300, 300);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
}
}

Answer 1

UPD2:

您的代码已修复。还有很多其他问题，例如：每次拖动鼠标时都会在列表中添加一个点，等等。它远非完美，但已经有足够的变化供您分析。

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.RenderingHints;
import java.awt.Shape;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.awt.geom.Line2D;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class LinesDemo extends JPanel {

private List<Line2D> linesList = new ArrayList<>();
private Line2D line = new Line2D.Double();
Point pointStart = null;
Point pointEnd   = null;
// Width and height of rectangular region around mouse
// pointer to use for hit detection on lines
private static final int HIT_BOX_SIZE = 4;

/**
 * Create the panel.
 */
public LinesDemo() {

    addMouseListener(new MouseAdapter() {
        @Override
        public void mousePressed(MouseEvent e) {
            pointStart = e.getPoint();
            pointEnd = e.getPoint();
            line = new Line2D.Double(pointStart, pointEnd);
            linesList.add(line);
        }

        @Override
        public void mouseReleased(MouseEvent e) {
            line.setLine(pointStart, pointEnd);
            pointStart = null;
        }

        @Override
        public void mouseClicked(MouseEvent e) {
            int x = e.getX();
            int y = e.getY();
            getClickedLine(x, y);
        }
    });

    addMouseMotionListener(new MouseMotionAdapter() {
        @Override
        public void mouseMoved(MouseEvent e) {
            pointEnd = e.getPoint();
        }

        @Override
        public void mouseDragged(MouseEvent e) {
            pointEnd = e.getPoint();
            line.setLine(pointStart, pointEnd);
            repaint();
        }
    });
}

private Shape getClickedLine(int x, int y) {

    int boxX = x - HIT_BOX_SIZE / 2;
    int boxY = y - HIT_BOX_SIZE / 2;

    int width = HIT_BOX_SIZE;
    int height = HIT_BOX_SIZE;

    for(Line2D selectedLine:linesList) {
        if (selectedLine.intersects(boxX, boxY, width, height)) {
            System.out.println("intersects!");
            removeLine(selectedLine);
            return selectedLine;
        }
    }
    return null;
}

private void removeLine(Line2D line) {
    Iterator<Line2D> it = linesList.iterator();
    while(it.hasNext()) {
        Line2D selectedLine = it.next();
        if(selectedLine.equals(line)) {
            it.remove();
            repaint();
        }
    }
}

@Override
public void paintComponent(Graphics g){
    super.paintComponent(g);
    Graphics2D g2d = (Graphics2D) g;
    g2d.setPaint(Color.RED);
    g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    for(Shape content : linesList){
        g2d.draw(content);
    }
    g2d.dispose();
}

@Override
public Dimension getPreferredSize() {
    return new Dimension(300, 300);
}

public static void main(String[] args) {
    JFrame frame = new JFrame("Moving and Scaling");
    LinesDemo m = new LinesDemo();
    frame.add(m);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(300, 300);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
}
}

原文：我不能运行你的程序，但你可以尝试替换

while(it.hasNext()) {
    Line2D selectedLine = it.next();
    if(selectedLine.equals(line)) {
        it.remove();
        repaint();
    }
}

和

boolean repaintNeeded = false;
while(it.hasNext()) {
    Line2D selectedLine = it.next();
    if(selectedLine.equals(line)) {
        it.remove();
        repaintNeeded = true;
    }
}
if (repaintNeeded) {
  repaint();
}

UPD1：我能够运行你的代码。其实有很多地方需要改进。具体针对您的问题，这两件事导致您的线条未被绘制：

    @Override
    public void mouseReleased(MouseEvent e) {
        pointStart = null;
    }

和

if(pointStart != null) {

所以每次松开鼠标，你的代码都不会绘制任何东西。

Answer 2

线条消失的原因是您在 paintComponent():

中明确抑制了它们的绘制

if (pointStart != null) {

pointStart 已在 mouseReleased 中设置为 null，因此绘制了 none 条线。删除该检查，您的代码将按预期工作。

附带说明一下，您应该在 event dispatch thread 中创建 GUI。

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