更改 JButton 焦点区域

Question

如何更改 JButton 上的焦点区域，以便当我将光标悬停在按钮上时，我的服装翻转图标不会在光标位于实际按钮本身之前稍微激活。

Answer 1

按钮的contains(x, y) 方法确定鼠标何时进入按钮。如果您的自定义按钮不是矩形，那么您需要重写此方法。

这是一个演示这个概念的旧示例：

// Old example code found on the internet somewhere
// to paint a Round button with hit detection

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

public class RoundButton extends JButton
{
    public RoundButton(String label)
    {
        super(label);

        // These statements enlarge the button so that it
        // becomes a circle rather than an oval.
        Dimension size = getPreferredSize();
        size.width = size.height = Math.max(size.width, size.height);
        setPreferredSize(size);
        setSize(size);

        // This call causes the JButton not to paint the background.
        // This allows us to paint a round background.
        setContentAreaFilled(false);
    }

    // Paint the round background and label.
    protected void paintComponent(Graphics g)
    {
        if (getModel().isArmed()) {
                // You might want to make the highlight color
                // a property of the RoundButton class.
                g.setColor(Color.lightGray);
            } else {
                g.setColor(getBackground());
            }
        g.fillOval(0, 0, getSize().width-1, getSize().height-1);

            // This call will paint the label and the focus rectangle.
        super.paintComponent(g);
    }

    // Paint the border of the button using a simple stroke.
    protected void paintBorder(Graphics g)
    {
        g.setColor(getForeground());
        g.drawOval(0, 0, getSize().width-1, getSize().height-1);
    }

    // Hit detection.
    Shape shape;

    public boolean contains(int x, int y)
    {
        // If the button has changed size, make a new shape object.
        if (shape == null || !shape.getBounds().equals(getBounds())) {
            shape = new Ellipse2D.Float(0, 0, getWidth(), getHeight());
        }
        return shape.contains(x, y);
    }

    private static void createAndShowUI()
    {
        // Create buttons that overlap one another

        JButton button = new RoundButton("Jackpot");
        button.setBackground(Color.green);
        button.setLocation(0, 0);

        JButton button2 = new RoundButton("Jackpot2");
        button2.setBackground(Color.red);
        button2.setLocation(40, 40);

        // Create a frame in which to show the button.
        JFrame frame = new JFrame("Round Button");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setBackground(Color.yellow);
        frame.setLayout(null);
        frame.add(button);
        frame.add(button2);
        //frame.setLayout(new FlowLayout());
        frame.setLocationByPlatform( true );
        frame.setSize(250, 200);
        frame.setVisible(true);

        MouseListener mouseListener = new MouseAdapter()
        {
            public void mouseEntered( MouseEvent e ) {}

            public void mouseExited( MouseEvent e ) {}

            public void mouseClicked( MouseEvent e )
            {
                System.out.println( "clicked " );
            }

            public void mousePressed( MouseEvent e )
            {
                System.out.println( "pressed " );
            }

            public void mouseReleased( MouseEvent e )
            {
                System.out.println( "released " );
            }
        };

        button.addMouseListener( mouseListener );
    }

    public static void main(String[] args)
    {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                createAndShowUI();
            }
        });
    }
}