java - 自定义边框外的组件绘制

Question

在这个自定义边框类中，我定义了一个 RoundRectangle2D 形状。该对象用于绘制边框。不幸的是，由于 JComponent 的 paint 方法在 paintBorder 之前调用了 paintComponent，因此设置了 Graphics 剪辑到 RoundRectangle2D 形状没有效果；即使我发出一个 repaint。因此，该组件将在其边界外绘制，这是可以理解的，这是不可取的。

所以，我想知道:如何让组件在自定义边框内独占绘制？

我考虑的一种方法是在 paintComponent 方法中获取组件的 Border 对象。然后将此对象转换到适当的类，我在其中定义将影响剪辑的参数。但这似乎不是一个“合理”的设计。

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编辑 -

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Insets;
import java.awt.RenderingHints;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.border.AbstractBorder;

class JRoundedCornerBorder extends AbstractBorder 
{   
    private static final long serialVersionUID = 7644739936531926341L;
    private static final int THICKNESS = 2;

    JRoundedCornerBorder()
    {
        super();
    }

    @Override
    public void paintBorder(Component c, Graphics g, int x, int y, int width, int height) 
    {
        Graphics2D g2 = (Graphics2D)g.create();

        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        if(c.hasFocus())
        {
            g2.setColor(Color.BLUE);
        }
        else
        {
            g2.setColor(Color.BLACK);
        }
        g2.setStroke(new BasicStroke(THICKNESS, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));
        g2.drawRoundRect(THICKNESS, THICKNESS, width - THICKNESS - 2, height - THICKNESS - 2, 20, 20);

        g2.dispose();
    }

    @Override
    public Insets getBorderInsets(Component c) 
    {
        return new Insets(THICKNESS, THICKNESS, THICKNESS, THICKNESS);
    }

    @Override
    public Insets getBorderInsets(Component c, Insets insets) 
    {
        insets.left = insets.top = insets.right = insets.bottom = THICKNESS;
        return insets;
    }

    public boolean isBorderOpaque() {
        return false;
    }

    public static void main(String[] args) 
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            @Override
            public void run() 
            {
                final JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new FlowLayout());

                // Add button with custom border
                final JButton button = new JButton("Hello");
                button.setBorder(new JRoundedCornerBorder());
                button.setBackground(Color.YELLOW);
                button.setPreferredSize(new Dimension(200, 200));
                frame.add(button);

                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }
}

红色圆圈突出显示组件超出其边界的位置。

Answer 1

啊...终于我明白了(由于某种原因错过了 roundBorder，我的错 :-) 按钮只是遵守它的契约(Contract):它声明是不透明的，所以必须填充它的完整区域，包括边界。所以设置一个剪辑(你可以在 paintComponent 中做)会违反契约(Contract):

 // DO NOT - a opaque component violates its contract, as it will not fill
 // its complete area  
        @Override
        protected void paintComponent(Graphics g) {
            if (getBorder() instanceof JRoundedCornerBorder) {
                Shape borderShape = ((JRoundedCornerBorder) getBorder()).
                    getBorderShape(getWidth(), getHeight());
                g.setClip(borderShape);
            }
            super.paintComponent(g);
        }

丑陋但安全的方法是将自己报告为透明并自己接管背景绘画:

        @Override
        protected void paintComponent(Graphics g) {
            if (getBorder() instanceof JRoundedCornerBorder) {
                g.setColor(getBackground());
                Shape borderShape = ((JRoundedCornerBorder) getBorder())
                    .getBorderShape(getWidth(), getHeight());
                ((Graphics2D) g).fill(borderShape);
            }
            super.paintComponent(g);
        }

        @Override
        public boolean isContentAreaFilled() {
            if (getBorder() instanceof JRoundedCornerBorder) return false;
            return super.isContentAreaFilled();
        }

        // using
        button.setOpaque(false);