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出于某种原因，当我将 ClockComponent 对象添加到 JPanel 对象时，它没有显示出来。当我将它添加到 JFrame 对象而不是 JPanel 对象时，它确实会显示出来......我不明白为什么，我在这里发布这个问题之前已经查过了，但无济于事。有什么方法可以让我的从 JComponent 继承的 ClockComponent 对象显示在 JPanel 上？非常感谢您提前提供的帮助。

这是我的 ClockViewer 类，它在运行时不会显示时钟：

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

            public class ClockViewer
            {
                public static void main(String[] args)
                {
                    JFrame frame = new JFrame();
                    frame.setTitle("Clock viewer");
                    frame.setSize(500, 500);
                    JPanel panel = new JPanel();

                    ClockComponent comps = new ClockComponent(7, 40);

                    panel.add(comps);
                    frame.add(panel);

                    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                    frame.setVisible(true);
                }
            }

这是我的 ClockComponent 类供参考：

            import java.awt.Graphics;
            import java.awt.Graphics2D;
            import java.awt.geom.Ellipse2D;
            import java.awt.geom.Line2D;

            import javax.swing.JComponent;

            public class ClockComponent extends JComponent
            {
                final int CENTER = 150;
                final double HOUR_HAND_LENGTH = 20;
                final double MINUTE_HAND_LENGTH = 40;

                private Line2D.Double hourHand;
                private Line2D.Double minuteHand;

                public ClockComponent(double hour, double minute)
                {
                    hourHand = new Line2D.Double(CENTER, CENTER, 
                            CENTER, CENTER - HOUR_HAND_LENGTH);
                    minuteHand = new Line2D.Double(CENTER, CENTER, 
                            CENTER, CENTER - MINUTE_HAND_LENGTH);

                    final int HOURS_ON_CLOCK = 12;
                    final int MINUTES_IN_HOUR = 60;
                    final double HOURS_TO_RADIANS = 2 * Math.PI / HOURS_ON_CLOCK;
                    final double MINUTES_TO_RADIANS = 2 * Math.PI / MINUTES_IN_HOUR;

                    hourHand.setLine(CENTER, CENTER, CENTER + HOUR_HAND_LENGTH * 
                            Math.sin((hour + minute / MINUTES_IN_HOUR) * HOURS_TO_RADIANS), 
                            CENTER - HOUR_HAND_LENGTH * 
                            Math.cos((hour + minute / MINUTES_IN_HOUR) * HOURS_TO_RADIANS));
                    minuteHand.setLine(CENTER, CENTER,
                            CENTER + MINUTE_HAND_LENGTH * Math.sin(minute * MINUTES_TO_RADIANS),
                            CENTER - MINUTE_HAND_LENGTH * Math.cos(minute * MINUTES_TO_RADIANS));
                }

                public void paintComponent(Graphics g)
                {
                    final int DIAMETER = 100;
                    final int POS_X_Y = CENTER - DIAMETER / 2;

                    Graphics2D g2 = (Graphics2D) g;

                    Ellipse2D.Double clockFace = 
                            new Ellipse2D.Double(POS_X_Y, POS_X_Y, DIAMETER, DIAMETER);

                    g2.draw(clockFace);
                    g2.draw(hourHand);
                    g2.draw(minuteHand);
                }
            }
4

2 回答 2

3

在面板中，您可以使用使时钟组件填充面板的整个区域的布局，例如GridLayout：

JPanel panel = new JPanel(new GridLayout(1, 0));

面板的默认设置FlowLayout不会展开任何子组件。

于 2012-11-06T00:10:43.903 回答
2

ClockComponent应该设置或覆盖首选大小。如果组件不可调整大小，许多人更喜欢覆盖它。这个例子只是设置它。

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

public class ClockComponent extends JComponent
{
    final int CENTER = 150;
    final double HOUR_HAND_LENGTH = 20;
    final double MINUTE_HAND_LENGTH = 40;

    private Line2D.Double hourHand;
    private Line2D.Double minuteHand;

    public ClockComponent(double hour, double minute)
    {
        setPreferredSize(new Dimension(300,300));
        hourHand = new Line2D.Double(CENTER, CENTER, 
                CENTER, CENTER - HOUR_HAND_LENGTH);
        minuteHand = new Line2D.Double(CENTER, CENTER, 
                CENTER, CENTER - MINUTE_HAND_LENGTH);

        final int HOURS_ON_CLOCK = 12;
        final int MINUTES_IN_HOUR = 60;
        final double HOURS_TO_RADIANS = 2 * Math.PI / HOURS_ON_CLOCK;
        final double MINUTES_TO_RADIANS = 2 * Math.PI / MINUTES_IN_HOUR;

        hourHand.setLine(CENTER, CENTER, CENTER + HOUR_HAND_LENGTH * 
                Math.sin((hour + minute / MINUTES_IN_HOUR) * HOURS_TO_RADIANS), 
                CENTER - HOUR_HAND_LENGTH * 
                Math.cos((hour + minute / MINUTES_IN_HOUR) * HOURS_TO_RADIANS));
        minuteHand.setLine(CENTER, CENTER,
                CENTER + MINUTE_HAND_LENGTH * Math.sin(minute * MINUTES_TO_RADIANS),
                CENTER - MINUTE_HAND_LENGTH * Math.cos(minute * MINUTES_TO_RADIANS));
    }

    public void paintComponent(Graphics g)
    {
        final int DIAMETER = 100;
        final int POS_X_Y = CENTER - DIAMETER / 2;

        Graphics2D g2 = (Graphics2D) g;

        Ellipse2D.Double clockFace = 
                new Ellipse2D.Double(POS_X_Y, POS_X_Y, DIAMETER, DIAMETER);

        g2.draw(clockFace);
        g2.draw(hourHand);
        g2.draw(minuteHand);
    }

    public static void main(String[] args)
    {
        JFrame frame = new JFrame();
        frame.setTitle("Clock viewer");
        // bad practice
        //frame.setSize(500, 500);
        JPanel panel = new JPanel();

        ClockComponent comps = new ClockComponent(7, 40);

        panel.add(comps);
        frame.add(panel);
        // Good practice.
        frame.pack();

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}
于 2012-11-06T00:16:59.853 回答