java - JPanel 上的 Graphics2D 并将 JPanel 添加到 JFrame

Question

我正在尝试在 JPanel 上绘图并将其添加到我的 createAndShowGui 方法中的 JFrame 中。我尝试了一些不同的事情:在 createAndShowGui 方法中创建 JPanel、将绘图添加到 JFrame 等...最常见的一件事是，我看不到任何图形!

注意:我能够让图形显示在 JTabbedPane 中，但不能显示在 JPanel 上，这正是我真正希望它们显示的内容，以使代码更加面向对象。

编辑:这是工作概念独立示例:

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Ellipse2D;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

public class DrawPanelMain extends JPanel {

    /*
    * Variables used to set the value of preferred height and width
    */
    public static final double version = 0.0;
    JPanel switchPanel = new JPanel();
    JPanel testPanel = new JPanel();
    JPanel btnPanel = new JPanel();
    DrawEllipses drawEllipses = new DrawEllipses(POINT_LIST);

    public static void main(String[] args) {

        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                initializePointList();
                createAndShowGui();
            }
        });
    }

    public static java.util.List<Point> POINT_LIST = new ArrayList<>();

    /*
    * This loop will initialize POINT_LIST with the set of points for drawing the ellipses.
    * The for each loop initializes points for the top row and the second for loop draws the
    * right triangle.
    */
    public static void initializePointList() {

        int ellipsePointsYCoordinate[] = {140, 200, 260, 320, 380, 440, 500, 560, 620};
        int ellipsePointsXCoordinate[] = {140, 200, 260, 320, 380, 440, 500, 560, 620, 680};
        int xx = 80;

        for (int aXt : ellipsePointsXCoordinate) {
            POINT_LIST.add(new Point(aXt, xx));
        }

        for (int i = 0; i < ellipsePointsYCoordinate.length; i++) {
            for (int j = i; j < ellipsePointsYCoordinate.length; j++) {
                POINT_LIST.add(new Point(ellipsePointsXCoordinate[i], ellipsePointsYCoordinate[j]));
            }
        }
    }

    public DrawPanelMain() {

        testPanel.setBackground(Color.RED);
        switchPanel.add(drawEllipses);

        setLayout(new BorderLayout());
        add(switchPanel, BorderLayout.CENTER);
        add(testPanel, BorderLayout.EAST);
        add(btnPanel, BorderLayout.SOUTH);
        getPreferredSize();

        btnPanel.add(new JButton(new AddSwitchAction("Add Switch Panel")));
    }

    public static void createAndShowGui() {

        JFrame frame = new JFrame("RF Connection Panel " + version);

        frame.setLayout(new BorderLayout());
        frame.add(new DrawPanelMain());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationByPlatform(false);
        //frame.setLocationRelativeTo(null);
        frame.pack();
        frame.setVisible(true);
    }

    /*
    * AddSwitchAction will add a new pane to the tabbedPane when the add switch button is clicked
    */
    private class AddSwitchAction extends AbstractAction {
        public AddSwitchAction(String name) {
            super(name);
            int mnemonic = (int) name.charAt(0);
            putValue(MNEMONIC_KEY, mnemonic);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            int index = 0;
            DrawEllipses tabComponent = new DrawEllipses(POINT_LIST);
            switchPanel.add(tabComponent, index++);

        }
    }

}

@SuppressWarnings("serial")
class DrawEllipses extends JPanel {
    private final int PREF_W = 750; //Window width
    private final int PREF_H = 750; //Window height
    private static final int OVAL_WIDTH = 30;
    private static final Color INACTIVE_COLOR = Color.RED;
    private static final Color ACTIVE_COLOR = Color.green;
    private java.util.List<Point> points;
    private java.util.List<Ellipse2D> ellipses = new ArrayList<>();
    private Map<Ellipse2D, Color> ellipseColorMap = new HashMap<>();

    /*
     * This method is used to populate "ellipses" with the initialized ellipse2D dimensions
     */
    public DrawEllipses(java.util.List<Point> points) {
        this.points = points;
        for (Point p : points) {
            int x = p.x - OVAL_WIDTH / 2;
            int y = p.y - OVAL_WIDTH / 2;
            int w = OVAL_WIDTH;
            int h = OVAL_WIDTH;
            Ellipse2D ellipse = new Ellipse2D.Double(x, y, w, h);
            ellipses.add(ellipse);
            ellipseColorMap.put(ellipse, INACTIVE_COLOR);
        }

        MyMouseAdapter mListener = new MyMouseAdapter();
        addMouseListener(mListener);
        addMouseMotionListener(mListener);
    }

    /*
     * paintComponent is used to paint the ellipses
     */
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                RenderingHints.VALUE_ANTIALIAS_ON);
        for (Ellipse2D ellipse : ellipses) {
            g2.setColor(ellipseColorMap.get(ellipse));
            g2.fill(ellipse);
            g2.setColor(Color.BLACK);
            g2.setStroke(new BasicStroke(2));
            g2.draw(ellipse);
        }

        /*
         * Set the font characteristics, color, and draw the row labels.
         */
        g.setFont(new Font("TimesRoman", Font.BOLD, 18));
        g.setColor(Color.BLACK);

        //Along the top row
        g.drawString("External Port", 10, 50);
        g.drawString("1", 135, 50);
        g.drawString("2", 195, 50);
        g.drawString("3", 255, 50);
        g.drawString("4", 315, 50);
        g.drawString("5", 375, 50);
        g.drawString("6", 435, 50);
        g.drawString("7", 495, 50);
        g.drawString("8", 555, 50);
        g.drawString("9", 615, 50);
        g.drawString("10", 672, 50);

        //Along the Y-axis
        g.drawString("Radio 2", 40, 145);
        g.drawString("3", 90, 205);
        g.drawString("4", 90, 265);
        g.drawString("5", 90, 325);
        g.drawString("6", 90, 385);
        g.drawString("7", 90, 445);
        g.drawString("8", 90, 505);
        g.drawString("9", 90, 565);
        g.drawString("10", 90, 625);

        //Along the X-Axis
        g.drawString("1", 135, 670);
        g.drawString("2", 195, 670);
        g.drawString("3", 255, 670);
        g.drawString("4", 315, 670);
        g.drawString("5", 375, 670);
        g.drawString("6", 435, 670);
        g.drawString("7", 495, 670);
        g.drawString("8", 555, 670);
        g.drawString("9", 615, 670);

        //Draws a 3DRect around the top row of ellipse2D objects
        g2.setColor(Color.lightGray);
        g2.draw3DRect(120, 60, 580, 40, true);
        g2.draw3DRect(121, 61, 578, 38, true);
        g2.draw3DRect(122, 62, 576, 36, true);

    }

    /*
     * MouseAdapter is extended for mousePressed Event that detects if the x, y coordinates
     * of a drawn ellipse are clicked.  If the color is INACTIVE it is changed to ACTIVE and
     * vice versa.
     */
    private class MyMouseAdapter extends MouseAdapter {
        @Override
        /*
         * When mousePressed event occurs, the color is toggled between ACTIVE and INACTIVE
         */
        public void mousePressed(MouseEvent e) {
            Color c;
            for (Ellipse2D ellipse : ellipses) {
                if (ellipse.contains(e.getPoint())) {
                    c = (ellipseColorMap.get(ellipse) == INACTIVE_COLOR) ? ACTIVE_COLOR : INACTIVE_COLOR;
                    ellipseColorMap.put(ellipse, c);
                }
            }
            repaint();
        }
    }

    /*
* This method will set the dimensions of the JFrame equal to the preferred H x W
*/
    @Override
    public Dimension getPreferredSize() {
        if (isPreferredSizeSet()) {
            return super.getPreferredSize();
        }
        return new Dimension(PREF_W, PREF_H);
    }
}

Answer 1

switchPanel.add(title, tabComponent);

默认情况下，JPanel 使用 FlowLayout，它尊重组件的首选大小。组件的首选大小是 (0, 0)，因此无需绘制任何内容。另外，您使用的“标题”字符串是不正确的(并且如已经提到的那样已过时)。该字符串表示布局管理器的约束。你不能只创建一个字符串值。在任何情况下 FlowLayout 不接受任何约束，因此您应该使用:

switchPanel.add(tabComponent);

I am trying to draw on a JPanel

进行自定义绘制时，您需要重写面板的 getPreferredSize() ，以便布局管理器可以使用该信息。如果您不重写此方法，则大小为 (0, 0)，因此无需绘制任何内容。

编辑:

首先是一些一般性评论:

1. 不要对面板的尺寸进行硬编码。您的硬编码尺寸 (1200 x 750) 对于我的显示器来说太大了。如果您想要全屏，请使用 frame.setExtendedState(JFrame.MAXIMIZED_BOTH);

2. 发布您实际测试的代码。正如已经提到的，您发布的代码甚至没有将“switchPanel”添加到框架中。

3. 您尚未更新代码来展示如何重写 getPreferredSize() 方法。

最后，我在您的代码中看到您将面板动态添加到可见的 GUI 中。在这种情况下，一般代码应该是:

panel.add(....);
panel.revalidate(); // to invoke the layout manager otherwise size is still (0, 0)
panel.repaint();