java - 如何使 JButtons 在以图像为背景的 JPanel 上可见

Question

我制作了一个以图像作为背景的 JPanel。但是在第一次加载 JPanel 时，其余添加的组件但图像不可见。将鼠标悬停在图像上后，按钮就会变得可见。如何在加载面板时使 JButtons 与作为背景的图像一起可见。

这是我的代码片段:

    contentPane = new JPanel();
    contentPane.setBorder(new SoftBevelBorder(BevelBorder.LOWERED, null, null, null, null));
    setContentPane(contentPane);
    contentPane.setLayout(null);

    homePanel.setBounds(10, 11, 959, 620);
    homePanel.setLayout(null);

    JPanel wizardPanel = new JPanel();
    wizardPanel.setBounds(10, 295, 545, 336);
    wizardPanel.setLayout(null);
    homePanel.add(wizardPanel);

    JLabel backgroundLabel;
    try {
        backgroundLabel = new JLabel(new ImageIcon(ImageIO.read(new File("images/nature.jpg"))));
        backgroundLabel.setBounds(0, 0, 545, 336);
        wizardPanel.add(backgroundLabel);
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }


    JButton btnNewButton = new JButton("New button");
    btnNewButton.setBounds(309, 95, 89, 23);
    wizardPanel.add(btnNewButton);

    JButton btnNewButton_1 = new JButton("New button");
    btnNewButton_1.setBounds(309, 150, 89, 23);
    wizardPanel.add(btnNewButton_1);

    JButton btnNewButton_2 = new JButton("New button");
    btnNewButton_2.setBounds(309, 212, 89, 23);
    wizardPanel.add(btnNewButton_2);

Answer 1

把按钮放在标签上是个坏主意。更好的方法是将图像绘制为面板背景或使用 JLayer。这是第一个解决方案的示例:

import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.LayoutManager;
import java.util.Objects;

import javax.imageio.ImageIO;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;

public class JImagePanel extends JPanel {

    private final Image image;

    private boolean scale;

    public JImagePanel(Image anImage) {
        image = Objects.requireNonNull(anImage);
    }

    public JImagePanel(Image anImage, LayoutManager aLayout) {
        super(aLayout);
        image = Objects.requireNonNull(anImage);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        final Image toDraw = scale? image.getScaledInstance(getWidth(), getHeight(), Image.SCALE_SMOOTH) : image;
        g.drawImage(toDraw, 0, 0, this);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Dimension getPreferredSize() {
        if (isPreferredSizeSet()) {
            return super.getPreferredSize();
        } else {
            return new Dimension(image.getWidth(this), image.getHeight(this));
        }
    }

    public boolean isScale() {
        return scale;
    }

    public void setScale(boolean scale) {
        this.scale = scale;
    }


    public static void main(String[] args) throws Exception {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                try {
                    final JImagePanel p = 
                            new JImagePanel(ImageIO.read(JImagePanel.class.getResource("myImage.png")), new FlowLayout());
                    p.setScale(true);
                    p.add(new JButton("Button"));
                    final JFrame frm = new JFrame("Image test");
                    frm.add(p);
                    frm.pack();
                    frm.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
                    frm.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

}