单击鼠标后在JPanel上绘制圆圈

问题描述

我想在鼠标点击后才绘制圆圈。由于paintComponent方法调用自身，所以第一个圆绘制没有单击。

I want to draw circle only after mouse gets click. As paintComponent method called itself, so first circle draw without click.

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();
}

}

推荐答案

您的代码存在一些问题：

There are a few issues with your code:

1. 您永远不会调用 super.paintComponent（）;


2. 您只有一个 x 和 y


3. 请注意，当你调整框架的大小时，一些圆圈会消失，整体表现得很奇怪。


4. 我会存储所有 Point s用户点击了 ArrayList 然后在 paintComponent 方法。这样你就可以调用 super.paintComponent（）; 而不会使圆圈消失。



1. You never call super.paintComponent();
2. You only have one x and y
3. Note how when you resize the frame, some circles will disappear and it overall behaves in a strange way.
4. I would store all the Points where the user has clicked in an ArrayList and then loop through that list inside the paintComponent method. This way you can call super.paintComponent(); without the circles disappearing.

已更改，正常工作的代码：

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);
            }
        });
    }

}

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