Swing Netbeans构建器中不显示背景图像

Question

我在JFrame类上使用netbeans builder"design".我有传统的JFrame,我在其中添加了一个JPanel(使用构建器).

现在在代码中,我想为这个面板添加一个背景,如下所示:

public class NewJFrame extends javax.swing.JFrame {

    public NewJFrame() {
        initComponents();
        addBackground();
    }

    private void addBackground()
    {
        Image bgImage;
        try {
            bgImage = ImageIO.read(new File("src/general/Mockup.png"));
            jPanel1.add(new NewJFrame.ImagePanel(bgImage));
            jPanel1.repaint();
        } catch (IOException ex) {
            Logger.getLogger(NewJFrame.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    public static void main(String args[]) {

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new NewJFrame().setVisible(true);
            }
        });
    }
}

我没有看到任何东西,只是一个空的JFrame/JPanel.

顺便说一下,我将它用于ImagePanel代码

@SuppressWarnings("serial")
class ImagePanel extends JPanel {
    private Image image;

    ImagePanel(Image image) {
        this.image = image;
    };

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(image, 0, 0, getWidth(), getHeight(), this);
    }
}

Answer 1

• 你的班级ImagePanel extends JPanel {必须覆盖getPreferredSize(),

• 因为public void paintComponent(Graphics g) {(painting in Swing,Graphics(2D))没有返回任何大小的容器,简单的返回Dimmension(0, 0)

• JPanel已经在API中实现FlowLayout(仅接受PreferredSize来自其子节点的那些),然后您custom painting将永远不会在屏幕上看到