JTextArea圆角落

Question

我想让JTextArea有一个圆角，我做了这个代码：

public BPosTxtArea() {
    super();
    setOpaque(false);
}

@Override
protected void paintComponent(Graphics g) {
    Graphics2D g2 = (Graphics2D) g.create();
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    g2.setColor(getBackground());
    g2.fillRoundRect(0, 0, getWidth() - 1, getHeight() - 1, 15, 15);
    super.paintComponent(g);
}

@Override
protected void paintBorder(Graphics g) {
    Graphics2D g2 = (Graphics2D) g.create();
    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
    g2.setColor(new Color(102, 102, 102));
    g2.drawRoundRect(0, 0, getWidth() - 1, getHeight() - 1, 15, 15);
}

但它仍然有一个方形边框，如下图所示：

任何人都可以帮助我吗？

Answer 1

首先看一下How to Use Borders

这是一个非常简单的例子：

public class RoundBorder implements Border {

    private int radius;

    public RoundBorder(int radius) {
        this.radius = radius;
    }

    public int getRadius() {
        return radius;
    }

    @Override
    public void paintBorder(Component c, Graphics g, int x, int y, int width, int height) {
        Graphics2D g2d = (Graphics2D) g.create();
        g2d.draw(new RoundRectangle2D.Double(x, y, width - 1, height - 1, getRadius(), getRadius()));
        g2d.dispose();
    }

    @Override
    public Insets getBorderInsets(Component c) {
        int value = getRadius() / 2;
        return new Insets(value, value, value, value);
    }

    @Override
    public boolean isBorderOpaque() {
        return false;
    }

}

import java.awt.Component;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.geom.RoundRectangle2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.border.Border;

public class Example {

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

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

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

    public class TestPane extends JPanel {

        public TestPane() {
            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridwidth = GridBagConstraints.REMAINDER;

            JTextArea ta = new JTextArea(10, 20);
            ta.setBorder(new RoundBorder(20));

            JScrollPane sp = new JScrollPane(new JTextArea(10, 20));
            sp.setBorder(new RoundBorder(20));

            add(ta, gbc);
            add(sp, gbc);
        }

    }

    public class RoundBorder implements Border {

        private int radius;

        public RoundBorder(int radius) {
            this.radius = radius;
        }

        public int getRadius() {
            return radius;
        }

        @Override
        public void paintBorder(Component c, Graphics g, int x, int y, int width, int height) {
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.draw(new RoundRectangle2D.Double(x, y, width - 1, height - 1, getRadius(), getRadius()));
            g2d.dispose();
        }

        @Override
        public Insets getBorderInsets(Component c) {
            int value = getRadius() / 2;
            return new Insets(value, value, value, value);
        }

        @Override
        public boolean isBorderOpaque() {
            return false;
        }

    }

}

问题是，边框被绘制在“组件填充区域”内，这意味着角落将与填充区域颜色相同。使用Border无法绕过它。

诀窍是创建第二个组件，您可以在其上绘制边框（通过paintComponent，填充边框内与文本区域颜色相同的区域），然后将组件添加到其中

<强>更新

根据您的代码示例，您不会覆盖getInsets，这将非常重要，另一方面，您的JTextArea似乎在JScrollPane范围内...

public class BPosTextArea extends JTextArea {

    private int radius;

    public BPosTextArea() {
        super(10, 20);
        setOpaque(false);
        setBorder(null);
        setRadius(20);
    }

    @Override
    protected void paintComponent(Graphics g) {
        Graphics2D g2 = (Graphics2D) g.create();
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setColor(getBackground());
        g2.fillRoundRect(0, 0, getWidth() - 1, getHeight() - 1, getRadius(), getRadius());
        super.paintComponent(g);
    }

    @Override
    protected void paintBorder(Graphics g) {
        Graphics2D g2 = (Graphics2D) g.create();
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setColor(new Color(102, 102, 102));
        g2.drawRoundRect(0, 0, getWidth() - 1, getHeight() - 1, getRadius(), getRadius());
    }

    public void setRadius(int radius) {
        this.radius = radius;
        repaint();
    }

    public int getRadius() {
        return radius;
    }

    @Override
    public Insets getInsets() {
        int value = getRadius() / 2;
        return new Insets(value, value, value, value);
    }

}

解决方案是为border

设置null到JScrollPane