Java图形:通过2D线连接点

Question

我是Java新手，我想创建一个非常简单的绘图GUI，用户可以在其中绘制简单的表单，点击面板，当鼠标在一个位置按下并在另一个位置释放(拖放(时，用一条线连接不同的点。点和线应该存储在两个ArrayList中。单击时，我设法在面板上找到了点，但每次鼠标放下并创建另一个点时，线都会改变坐标。我试了很多次，但我不知道如何让线条留在面板上；trace"；拖放活动。

提前感谢您的每一个提示！

import java.util.ArrayList;
import java.util.Arrays;
import java.awt.*;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.geom.Line2D;
import java.awt.geom.Line2D.Double;
import javax.swing.JPanel;
public class PaintPanel extends JPanel {
private ArrayList<Point> pointList;
private ArrayList<Line2D.Double> lineList;
private Point point1, point2;
private Line2D line;
public PaintPanel() {
pointList = new ArrayList<Point>();
lineList = new ArrayList<Line2D.Double>();
addMouseListener(new PaintListener());
}
//takes as parameter objekt of Class Graphics
public void paintComponent(Graphics g) {
// calls constructor of SuperClass 
super.paintComponent(g);
this.setBackground(Color.white);
// color to draw
g.setColor(Color.black);
for(Point spot : pointList) {
g.fillOval(spot.x,spot.y, 10, 10);
if(point1 != null & point2 !=null) {
Graphics2D g2 =(Graphics2D) g;
line = new Line2D.Double(point1.getX(), point1.getY(), point2.getX(), point2.getY());
lineList.add((Double) line);
g2.draw(line);
}

}
}

private class PaintListener implements MouseListener{
@Override
public void mouseClicked(MouseEvent e) {
}
@Override
public void mousePressed(MouseEvent e) {
point1 = e.getPoint();
pointList.add(point1);
repaint();
}
public void mouseDragged(MouseEvent e) {
}
@Override
public void mouseReleased(MouseEvent e) {
point2 = e.getPoint();
pointList.add(point2);
repaint();
}
@Override
public void mouseEntered(MouseEvent e) {
// TODO Auto-generated method stub
}
@Override
public void mouseExited(MouseEvent e) {
// TODO Auto-generated method stub
}

}
}

Answer 1

我已经重新创建了您要做的事情，我添加了代码注释来帮助您完成这个过程。

该程序从一组点开始，您可以用线连接这些点，也可以通过右键单击添加更多点。

您需要实现MouseMotionListener和MouseListener(如下所示(，因为这将允许您跟踪鼠标的所有操作。

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.ArrayList;
import javax.swing.*;

public class PaintPanel extends JPanel implements MouseListener, MouseMotionListener {
//ARRAYLIST OF ALL POINTS
public ArrayList<Point2D.Double> points = new ArrayList<Point2D.Double>();
//ARRAYLIST OF ALL LINES
public ArrayList<Line2D.Double> lines = new ArrayList<Line2D.Double>();
//START POINT OF A NEW LINE
public Point2D.Double startPoint;
//CURRENT MOUSE LOCATION
public Point2D.Double mouse = null;
//TRUE IF USER IS DRAGGING
public boolean dragging = false;
//THE SIZE OF THE POINTS
public int pointSize = 20;
public static void main(String[] args) {
JFrame frame = new JFrame();
PaintPanel stage = new PaintPanel();
stage.setBackground(new Color(47, 47, 47));
stage.setPreferredSize(new Dimension(1000, 1000));
stage.addMouseListener(stage);
stage.addMouseMotionListener(stage);
frame.setContentPane(stage);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public PaintPanel() {
//ADDING POINTS TO THE CANVAS
for (int i = 1; i < 10; i++)
for (int j = 1; j < 10; j++)
points.add(new Point2D.Double(100 * i, j * 100));
}
public void paintComponent(Graphics graphics) {
super.paintComponent(graphics);
Graphics2D g2 = (Graphics2D) graphics;

//MAKING IT LOOK NICER
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g2.setStroke(new BasicStroke(2));
//DRAWING CURRENTLY DRAGGING LINE
if (dragging && startPoint != null) {
g2.setColor(Color.WHITE);
g2.drawLine((int) startPoint.x, (int) startPoint.y, (int) mouse.x, (int) mouse.y);
}

//DRAWING ALL THE LINES
for (int i = 0; i < lines.size(); i++) {
g2.setColor(Color.WHITE);
Line2D l = lines.get(i);
g2.drawLine((int) l.getX1(), (int) l.getY1(), (int) l.getX2(), (int) l.getY2());
}

//DRAWING ALL THE POINTS
for (int i = 0; i < points.size(); i++) {
Point2D.Double p = points.get(i);
g2.setColor(Color.WHITE);
g2.fillRoundRect((int) (p.x - (pointSize / 2)), (int) (p.y - (pointSize / 2)), pointSize, pointSize, pointSize, pointSize);
}
}
@Override
public void mousePressed(MouseEvent e) {

//ADD POINTS WITH RIGHT CLICK
if (SwingUtilities.isRightMouseButton(e)) {
mouse = new Point2D.Double(e.getX(), e.getY());
points.add(new Point2D.Double(e.getX(), e.getY()));
}
repaint();
}
@Override
public void mouseReleased(MouseEvent e) {
if (SwingUtilities.isLeftMouseButton(e)) {
mouse = new Point2D.Double(e.getX(), e.getY());

//IF THE USER HAS BEEN DRAGGING WHEN MOUSE RELEASED...
if (dragging) {
for (int i = 0; i < points.size(); i++) {
Point2D.Double p = points.get(i);
//IF THE USER FINISHED DRAGGING AT A POINT...
if (p.distance(mouse) < pointSize / 2) {
lines.add(new Line2D.Double(startPoint, p));
}
}
}
startPoint = null;
dragging = false;
}
repaint();
}
@Override
public void mouseDragged(MouseEvent e) {
if (SwingUtilities.isLeftMouseButton(e)) {
mouse = new Point2D.Double(e.getX(), e.getY());
dragging = true;
for (int i = 0; i < points.size(); i++) {
Point2D.Double p = points.get(i);
//IF THE USER STARTED DRAGGING ON A POINT...
if (p.distance(mouse) < pointSize / 2 && startPoint == null) {
startPoint = p;
}
}
}
repaint();
}
//UNUSED METHODS
@Override
public void mouseMoved(MouseEvent e) {}
@Override
public void mouseClicked(MouseEvent e) {}
@Override
public void mouseEntered(MouseEvent e) {}
@Override
public void mouseExited(MouseEvent e) {}

}