paintComponent()正在其他组件上绘制。

Question

我正在使用一个自定义类，基于这个答案中的代码，来绘制形状像对话气泡的背景。每当我调整窗口大小使得组件顶部或底部露出时，该组件的轮廓就会绘制在JScrollPane之外并覆盖其他组件，此时是JPanel。

在左侧图像中，由于组件仍然可见，因此绘制了JScrollPane底部的组件边框；而在右侧图像中，该组件不再可见，一切看起来都很正常。

我认为这与我使用JScrollPane来容纳组件有关，从而允许组件滑动到JPanel下方。如何防止这种情况发生？

主要：

public class Main {
    public static void main(String[] args) {
        JPanel panel = new JPanel(), panelbar = new JPanel();
        panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
        panelbar.setLayout(new FlowLayout());

        JScrollPane scroll = new JScrollPane(panel,
                JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
                JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);

        JFrame frame = new JFrame("");
        frame.setLayout(new BorderLayout());
        frame.setSize(200, 223);

        for (int i = 0; i < 6; i++) {
            JLabel label = new JLabel("JLabel");
            label.setBorder(new CustomBorder());
            label.setOpaque(true);
            label.setBackground(Color.ORANGE);
            panel.add(label);
        }

        panelbar.add(new JLabel("JPanel"));

        frame.add(scroll, BorderLayout.CENTER);
        frame.add(panelbar, BorderLayout.SOUTH);

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

自定义类：

public class CustomBorder extends AbstractBorder {
    private static final long serialVersionUID = 1L;
    Insets i;

    CustomBorder() {
        i = new Insets(10, 20, 10, 20);
    }

    @Override
    public void paintBorder(Component c, Graphics g, int x, int y, int width, int height) {
        super.paintBorder(c, g, x, y, width, height);

        Polygon bubble = new Polygon();
        bubble.addPoint(x + 10, y + 5);
        bubble.addPoint(x + width - 10, y + 5);
        bubble.addPoint(x + width - 10, y + height / 3);
        bubble.addPoint(x + width, y + height / 2);
        bubble.addPoint(x + width - 10, y + height * 2 / 3);
        bubble.addPoint(x + width - 10, y - 5 + height);
        bubble.addPoint(x + 10, y - 5 + height);

        Graphics2D g2d = (Graphics2D) g;
        Area rect = new Area(new Rectangle(x, y, width, height));
        rect.subtract(new Area(bubble));
        g2d.setClip(rect);
        g2d.setColor(c.getParent().getBackground());
        g2d.fillRect(0, 0, width, height);
        g2d.setClip(null);
        g2d.setColor(Color.BLACK);
        g2d.draw(bubble);
    }

    @Override
    public Insets getBorderInsets(Component c) {
        return i;
    }

    @Override
    public Insets getBorderInsets(Component c, Insets insets) {
        return i;
    }
}

- Spitz

---

这个 g2d.setClip(rect); 会引起问题，因为您已更改了原始的 Graphics 上下文的剪辑，现在允许您在不应该绘制的位置绘画，这就是为什么我不玩剪辑的原因。相反，制作一个与您试图生成的形状匹配的 Shape 并 draw/fill它。 - MadProgrammer

知道吗：在调用paintComponent后，Border被绘制，这意味着它们覆盖内容...这意味着如果您填充边框，则会覆盖内容... - MadProgrammer

@MadProgrammer draw/fill 会在文本上方绘制，而不是在文本后面，使 JLabel 内部的文本无法阅读。 - Spitz

这就是我的观点，边框本来就不应该被填充。 - MadProgrammer

我正在回复你的第一条评论。 - Spitz

Answer 1

这段剪切代码存在两个问题：

1. 在减去气泡时没有从原始剪辑开始（导致组件被绘制在滚动面板外部）
2. 在绘制气泡之前没有恢复原始剪辑：

修改后的代码应该是：

@Override
public void paintBorder(Component c, Graphics g, int x, int y, int width, int height) {
    super.paintBorder(c, g, x, y, width, height);

    Polygon bubble = new Polygon();
    bubble.addPoint(x + 10, y + 5);
    bubble.addPoint(x + width - 10, y + 5);
    bubble.addPoint(x + width - 10, y + height / 3);
    bubble.addPoint(x + width, y + height / 2);
    bubble.addPoint(x + width - 10, y + height * 2 / 3);
    bubble.addPoint(x + width - 10, y - 5 + height);
    bubble.addPoint(x + 10, y - 5 + height);

    Graphics2D g2d = (Graphics2D) g;
    //Area rect = new Area(new Rectangle(x, y, width, height));
    Shape clip = g2d.getClip();
    Area rect = new Area(clip);
    rect.subtract(new Area(bubble));
    g2d.setClip(rect);
    g2d.setColor(c.getParent().getBackground());
    g2d.fillRect(0, 0, width, height);
    //g2d.setClip(null);
    g2d.setClip(clip);
    g2d.setColor(Color.BLACK);
    g2d.draw(bubble);
}

- camickr

Answer 2

您的基本问题是，您正在更改剪辑区域，该区域在组件被绘制之前设置为某些其他内容，这使得您可以在组件边界之外进行绘制...

正如在这里和这里所讨论的那样，边框并不意味着要填充，也不会影响由paintComponent所填充的区域。

如果您查看深入了解绘图机制，您将会看到在调用paintBorder方法之前会调用paintComponent方法...

javax.swing.JComponent扩展了这个类，并将paint方法进一步分解成三个单独的方法，按以下顺序调用它们：

• protected void paintComponent(Graphics g)
• protected void paintBorder(Graphics g)
• protected void paintChildren(Graphics g)

那么，解决办法是什么？ 模拟吧！

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.Polygon;
import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.border.EmptyBorder;

public class BorderCheat {

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

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

                JPanel panel = new JPanel(), panelbar = new JPanel();
                panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
                panelbar.setLayout(new FlowLayout());

                JScrollPane scroll = new JScrollPane(panel,
                        JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
                        JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);

                for (int i = 0; i < 6; i++) {
                    BubblePane bp = new BubblePane();
                    bp.setBackground(Color.ORANGE);
                    JLabel label = new JLabel("JLabel");
                    bp.add(label);
                    panel.add(bp);
                }

                panelbar.add(new JLabel("JPanel"));

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(scroll);
                frame.add(panelbar, BorderLayout.SOUTH);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class BubblePane extends JPanel {

        public BubblePane() {
            setLayout(new GridBagLayout());
            setBorder(new EmptyBorder(10, 20, 10, 30));
            setOpaque(false);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            Insets insets = getInsets();
            int x = 0;
            int y = 0;
            int width = getWidth();
            int height = getHeight();
            Polygon bubble = new Polygon();
            bubble.addPoint(x, y);
            bubble.addPoint(x + width - insets.right + 10, y);
            bubble.addPoint(x + width - insets.right + 10, y + height / 3);
            bubble.addPoint(x + width, y + height / 2);
            bubble.addPoint(x + width - insets.right + 10, y + height * 2 / 3);
            bubble.addPoint(x + width - insets.right + 10, y + height);
            bubble.addPoint(x, y + height);

            g2d.setColor(getBackground());
            g2d.fill(bubble);
            g2d.setColor(Color.BLACK);
            g2d.draw(bubble);
            g2d.dispose();
        }

    }

}

好的，“但它们之间没有间隙”你说。那么，使用CompoundBorder或布局，允许您指定组件之间的垂直或水平间距...

- MadProgrammer