单击鼠标后在JPanel上绘制圆圈

Question

我只想在鼠标单击后绘制圆圈。由于paintComponent方法调用了自身，因此首先绘制圆而无需单击。

public class DrawPanel extends JPanel implements MouseListener {
private static final long serialVersionUID = 1L;
int x, y;

public DrawPanel() {
    setBackground(Color.WHITE);
    addMouseListener(this);
}

public void paintComponent(Graphics g) {
    Graphics2D g2 = (Graphics2D) g;
    g2.setColor(Color.red);
    g2.fillOval(x, y, 20, 20);
}

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

}

Answer 1

您的代码存在一些问题：

1. 你永远不会打电话 super.paintComponent();
2. 你只需要一个x和y
3. 请注意，当您调整框架大小时，某些圆圈将消失，并且总体上以奇怪的方式表现。
4. 我会将所有Points 存储在用户单击的位置ArrayList，然后在paintComponent方法内部遍历该列表。这样您就可以通话，super.paintComponent();而圈子不会消失。

更改后的工作代码：

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.RenderingHints;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;

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

public class DrawPanel extends JPanel {
    private static final long serialVersionUID = 1L;
    private ArrayList<Point> points;

    public DrawPanel() {
        points = new ArrayList<Point>();
        setBackground(Color.WHITE);
        addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                points.add(new Point(e.getX(), e.getY()));
                repaint();
            }
        });
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setColor(Color.red);
        for (Point point : points) {
            g2.fillOval(point.x, point.y, 20, 20);
        }
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.add(new DrawPanel());
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setSize(400, 400);
                frame.setVisible(true);
            }
        });
    }

}