在JPanel中添加JPanel - 不会显示嵌套的JPanel

Question

新规范

package test;

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


public class TestWindow extends JFrame{
//------------------------------------------------------------------------------
    public static void main(String[] args) {
        new TestWindow();
    }
//------------------------------------------------------------------------------
    public TestWindow(){
        setSize(300,300);
        this.setUndecorated(true);
        add(new Background());
        setVisible(true);
    }
//------------------------------------------------------------------------------

    private class Background extends JPanel{
        public Background(){
            add(b);
            repaint();
        }
//------------------------------------------------------------------------------    
        Bubble b = new Bubble();
        @Override
        public void paintComponent(Graphics g){
            super.paintComponent(g);
            Color c = Color.cyan;
            g.setColor(c);
            g.fillRect(0, 0,getWidth(), getHeight());
        }
//------------------------------------------------------------------------------
        private class Bubble extends JPanel{
            @Override
            public void paintComponent(Graphics g){
                super.paintComponent(g);
                g.setColor(Color.green);
                g.drawOval(0, 0, Background.this.getWidth(), Background.this.getHeight());
            }
        }
//------------------------------------------------------------------------------
    }
}  

产量

问题

目的是在其上绘制一个带有绿色圆圈的青色窗口.稍后我会将组件添加到绿色圆圈,这样看起来就像有一个带有青色背景的窗口和一个带有组件的绿色圆圈.
然而输出只是青色背景.没有圈子.

我尝试将XOR模式设置为青色,但这也不起作用.我是否错误地嵌套了这些类？

Answer 1

主要问题是......

    public void paintComponent(Graphics g){
        super.paintComponent(g);
        Color c = Color.cyan;
        g.setColor(c);
        g.fillRect(0, 0,getWidth(), getHeight());
        add(b);
        repaint();
    }

不仅在你的paint方法中向你的容器添加组件,你也在调用repaint,所有这些都将密谋反对你.

对于Mehta来说,当需要更新组件时,由reapint管理器调用Paint.你永远不应该调用任何可能使它无效的方法,否则需要重新绘制组件,这样做会让你失去CPU消耗的滑坡.

代替.

1. 在Bubble组件的构造函数中添加Background组件
2. 覆盖getPreferredSize这两个组件的方法并提供有用的提示,以便布局管理器了解组件可能实际使用的空间大小

您面临的主要问题(除了糟糕的绘画之外)是组件报告自己不需要高度或宽度,这意味着当布局管理器将它们布局时,它们实际上是不可见的

更新

我建议你看看

• 使用Swing创建GUI,特别注意布局管理器部分
• 定制绘画
• 在AWT和Swing中绘画

复活节彩蛋

为了获得建议和努力,让我给你一点帮助......

我建议你做的是阅读代码,回到Java Docs和教程并尝试弄清楚发生了什么;)

public class CircleControl {

    public static void main(String[] args) {
        new CircleControl();
    }

    public CircleControl() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setLayout(new GridBagLayout());
            add(new Bubble());
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 300);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);

            Graphics2D g2d = (Graphics2D) g.create();

            Color startColor = brighten(Color.CYAN, 0.75f);
            Color endColor = brighten(Color.CYAN, 0.5f);

            LinearGradientPaint lgp = new LinearGradientPaint(
                            new Point(0, 0),
                            new Point(0, getHeight()),
                            new float[]{0f, 1f},
                            new Color[]{startColor, endColor});

            g2d.setPaint(lgp);
            g2d.fill(new Rectangle(getWidth(), getHeight()));
            g2d.dispose();

        }
    }

    public class Bubble extends JPanel {

        public Bubble() {
            Font font = UIManager.getFont("Label.font");
            setFont(font.deriveFont(Font.BOLD, 48));
            setForeground(Color.WHITE);
            setBackground(darken(Color.CYAN, 0.3f));
            setOpaque(false);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(150, 150);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.setRenderingHint(RenderingHints.KEY_ALPHA_INTERPOLATION, RenderingHints.VALUE_ALPHA_INTERPOLATION_QUALITY);
            g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            g2d.setRenderingHint(RenderingHints.KEY_COLOR_RENDERING, RenderingHints.VALUE_COLOR_RENDER_QUALITY);
            g2d.setRenderingHint(RenderingHints.KEY_DITHERING, RenderingHints.VALUE_DITHER_ENABLE);
            g2d.setRenderingHint(RenderingHints.KEY_FRACTIONALMETRICS, RenderingHints.VALUE_FRACTIONALMETRICS_ON);
            g2d.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
            g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
            g2d.setRenderingHint(RenderingHints.KEY_STROKE_CONTROL, RenderingHints.VALUE_STROKE_PURE);
            g2d.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING, RenderingHints.VALUE_TEXT_ANTIALIAS_ON);

            int x = (getWidth() - 150) / 2;
            int y = (getHeight() - 150) / 2;

            Color startColor = brighten(getBackground(), 0.05f);
            Color endColor = getBackground();

            LinearGradientPaint lgp = new LinearGradientPaint(
                            new Point(x, y),
                            new Point(x, y + 150),
                            new float[]{0f, 1f},
                            new Color[]{startColor, endColor});
            g2d.setPaint(lgp);
            g2d.fill(new Ellipse2D.Double(x, y, 150, 150));

            FontMetrics fm = g2d.getFontMetrics();
            x = x + ((150 - fm.stringWidth("22")) / 2);
            y = y + ((150 / 2) + fm.getAscent());
            g2d.setColor(getForeground());
            g2d.drawString("22", x, y);

        }
    }

    public static Color brighten(Color color, double fraction) {
        int red = (int) Math.round(Math.min(255, color.getRed() + 255 * fraction));
        int green = (int) Math.round(Math.min(255, color.getGreen() + 255 * fraction));
        int blue = (int) Math.round(Math.min(255, color.getBlue() + 255 * fraction));
        int alpha = color.getAlpha();
        return new Color(red, green, blue, alpha);
    }

    public static Color darken(Color color, double fraction) {
        int red = (int) Math.round(Math.max(0, color.getRed() - 255 * fraction));
        int green = (int) Math.round(Math.max(0, color.getGreen() - 255 * fraction));
        int blue = (int) Math.round(Math.max(0, color.getBlue() - 255 * fraction));
        int alpha = color.getAlpha();
        return new Color(red, green, blue, alpha);
    }
}