我是 Java 新手，我想創建一個非常簡單的繪圖 GUI，其中用戶繪制簡單的表單，單擊面板并在滑鼠在一個位置按下并在另一個位置釋放時用一條線連接不同的點（拖動-和-下降）。點和線應存盤在兩個 ArrayList 中。單擊時我設法在面板上找到了點，但是每次放下滑鼠并創建另一個點時，線條都會改變坐標。我嘗試了很多次，但我不知道如何使線條保留在面板上并“跟蹤”拖放活動。
預先感謝您的每一個提示！
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
}
}
}
uj5u.com熱心網友回復：
我重新創建了您要執行的操作，并添加了代碼注釋以幫助您完成整個程序。
該程式從一組點開始，您可以將這些點與線連接起來，也可以通過右鍵單擊添加更多點。
您需要實作 MouseMotionListener 和 MouseListener（如下所示），因為這將允許您跟蹤滑鼠的所有操作。
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) {}
}
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