java - 在嵌套的 JPanel 上绘制组件 (Java)

Question

有人知道如何在 JPanel 中的 JPanel 上绘制圆圈吗？

基本上我在另一个 JPanel 中创建了一个新的 Circle 类，它扩展了 JComponent。然后我将其添加到其中一个面板并尝试重新绘制但没有显示任何内容。有任何想法吗？这是我的代码:

      class Circle extends JComponent 
{       
    @Override     public void paintComponent(Graphics g)
{
        super.paintComponent(g);
        g.drawOval(10,10, 11, 11);
        g.setColor(Color.RED);
        g.fillOval(10,10, 11, 11);                  
  } 
}


public void drawTest()
{
    Circle circle = new Circle();
    circle.setOpaque(false);
    circle.setSize(22, 22);
    circle.setVisible(true);
    circle.setBounds(11,11,11,5);
    jpanel.add(circle); 
    jpanel.repaint();

当我将圆圈添加到主面板 [add(circle) ] 但拒绝任何子面板时，代码有效。

Answer 1

您需要覆盖 getPreferredSize(...)方法就像你用 paintComponent(...) 方法一样，让它像这样:

public Dimension getPreferredSize()
{
    return (new Dimension(300, 300));
}

这里有一个示例程序可以为您提供进一步的帮助:

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

public class TwoButtons
{
    private int x;
    private int y;
    private int count = 0;

    private Timer timer;

    private ActionListener actionTimer; 

    public static void main(String args[])
    {
        Runnable runnable = new Runnable()
        {
            public void run()
            {
                TwoButtons gui = new TwoButtons();
                gui.go();
            }
        };      
        SwingUtilities.invokeLater(runnable);
    }

    public void go()
    {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel contentPane = new JPanel();

        /*
         * Class Name : 
         * Java Naming Convention says that class names 
         * should be in Pascal Case, i.e. the first
         * letter of the class name should be capitalized
         * and every new word must start with a capitalized 
         * Alphabet.
         * For Example : 
         * public class ClassName{...}
         * ----------------------------------------------------------
         * Variable Name : 
         * Java Naming Convention says that the variable name
         * should be in Camel Case, i.e. the first letter of 
         * the variable name should be small case or _ (underscore)
         * and every new word must start with a capitalized
         * Alphabet.
         * ---------------------------------------------------------
         */
        final MyDraw drawPanel = new MyDraw(70, 70);
        x = drawPanel.getXValue();
        y = drawPanel.getYValue();
        contentPane.add(drawPanel);

        actionTimer = new ActionListener()
        {
            public void actionPerformed(ActionEvent ae)
            {               
                x++;
                y++;
                if (count < 100)
                    drawPanel.setXYValues(x, y, count);
                else if (count == 100)
                    timer.stop();
                count++;
            }
        };

        frame.getContentPane().add(contentPane);
        frame.setSize(300,300);
        frame.setVisible(true);        

        timer = new Timer(40, actionTimer);
        timer.start();
    }
    class MyDraw extends JComponent
    {
        private int x;
        private int y;
        private int count = 0;
        private Timer timer;

        public MyDraw(int x, int y)
        {
            this.x = x;
            this.y = y;
        }

        public int getXValue()
        {
            return x;
        }

        public int getYValue()
        {
            return y;
        }

        public void setXYValues(int x, int y, int count)
        {
            this.x = x;
            this.y = y;
            this.count = count;
            repaint();
        }

        public Dimension getPreferredSize()
        {
            return (new Dimension(300, 300));
        }

        public void paintComponent(Graphics g)
        {
            g.setColor(Color.green);
            g.fillOval(x, y, 40, 40);
        }
    }
}