java 制作圆圈，然后在鼠标拖动事件上移动圆圈

Make circle and then move circle on mouse dragged event

提问by Jay

How to draw circle on mouse dragged event, and then how to move that circle on mouse dragged event in Java?

如何在鼠标拖动事件上绘制圆圈，然后在 Java 中如何在鼠标拖动事件上移动该圆圈？

My code is below.

我的代码如下。

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

class r extends JPanel {

    public int x1, x2, y1, y2, r, w, h,xDist,yDist;
    public static boolean flag = false, pressFlag = false;

    public r() {
        setBackground(Color.WHITE);
        addMouseListener(new MouseAdapter() {

            public void mousePressed(MouseEvent m) {
//                pressFlag = true;
                if (r > (int) Math.sqrt(Math.abs(m.getX() - x1) * Math.abs(m.getX() - x1) + Math.abs(m.getY() - y1) * Math.abs(m.getY() - y1))) {
                    flag = true;
                    yDist=xDist=x2 = y2 = 0;
                } else {
                    x1 = y1 = 0;
                    r=x2 = y2 = 0;
                    x1 = m.getX();
                    y1 = m.getY();
                }
                 repaint();
            }

            public void mouseReleased(MouseEvent m) {
                w = x2 - x1;
                h = y2 - y1;
                r = (int) Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
                flag = false;
            }
        });
        addMouseMotionListener(new MouseMotionAdapter() {

            public void mouseDragged(MouseEvent m) {
                if (flag && (x2!=0 && y2!=0)) {
                    xDist=(m.getX()-x2);
                    yDist=(m.getY()-y2);
                }
                x2 = m.getX();
                y2 = m.getY();

                repaint();
            }
        });
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        if (flag) {
            x1=x1+xDist;
            y1=y1+yDist;
            g.drawOval(x1, y1, w, h);
        } else {
            g.drawOval(x1, y1, x2 - x1, y2 - y1);
        }

    }
}

public class q extends JFrame {

    public static void main(String[] args) {
        JFrame jFrame = new JFrame();
        jFrame.setSize(300, 300);
        jFrame.add(new r());
        jFrame.setVisible(true);
        jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}

回答by Guillaume Polet

Something along those lines works nicely for me:

沿着这些路线的东西对我来说很好用：

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Ellipse2D;

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

class DragCircle extends JPanel {

    private final class MouseDrag extends MouseAdapter {
        private boolean dragging = false;
        private Point last;

        @Override
        public void mousePressed(MouseEvent m) {
            last = m.getPoint();
            dragging = isInsideEllipse(last);
            if (!dragging) {
                x = last.x;
                y = last.y;
                width = 0;
                height = 0;
            }
            repaint();
        }

        @Override
        public void mouseReleased(MouseEvent m) {
            last = null;
            dragging = false;
            repaint();
        }

        @Override
        public void mouseDragged(MouseEvent m) {
            int dx = m.getX() - last.x;
            int dy = m.getY() - last.y;
            if (dragging) {
                x += dx;
                y += dy;
            } else {
                width += dx;
                height += dy;
            }
            last = m.getPoint();
            repaint();
        }
    }

    private int x;
    private int y;
    private int width;
    private int height;

    private MouseDrag mouseDrag;

    public DragCircle() {
        setBackground(Color.WHITE);
        mouseDrag = new MouseDrag();
        addMouseListener(mouseDrag);
        addMouseMotionListener(mouseDrag);
    }

    public boolean isInsideEllipse(Point point) {
        return new Ellipse2D.Float(x, y, width, height).contains(point);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawOval(x, y, width, height);
    }

    public static void main(String[] args) {
        JFrame jFrame = new JFrame();
        jFrame.setSize(300, 300);
        jFrame.add(new DragCircle());
        jFrame.setVisible(true);
        jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
}