一个在图像中滑动的 UI

Question

我正在尝试更改在我的用户界面的 JLabel 中显示的图像。

下面的class是一个非常简单的概念测试。 UI 获取一个装满图像的文件夹（字段 imageFolderPath）并在唯一的 JLabel 中显示第一张调整大小的图像；点击图片提示UI在文件夹中显示如下图片。

至少，它应该。实际上，没有显示任何图像。错误显然是方法 reloadImage()，在重新缩放图像或重新绘制 JLabel 时，但我没有设法找到或纠正问题。有什么想法吗？

public class Test extends JFrame {

    private JPanel contentPane;
    private JLabel boardImage;
    private ImageIcon icon;

    public String imageFolderPath = "C:\modify\it\to\suit\your\needs\";
    public File[] files;
    public int indexImage = 0;

    public int imageResolution = 450;



    // =========================================================            
        // TODO | Constructors

    /**
     * Create the frame.
     */
    public Test() {
        if( !new File(imageFolderPath).exists() )
            new File(imageFolderPath).mkdir();
        this.files = new File(imageFolderPath).listFiles();

        System.out.println("Can show:");
        for( File file : files )
            System.out.println("\t"+file.getName());


        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, imageResolution, imageResolution);
        contentPane = new JPanel();
        contentPane.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent arg0) {
                // Every time the image is clicked, another one is shown
                indexImage++;
                reloadImage();
            }
        });
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(null);

        boardImage = new JLabel();
        boardImage.setBounds(0, 0, imageResolution, imageResolution);

        reloadImage();

        contentPane.add(boardImage);
    }

    // =========================================================            
        // TODO | Support methods

    /** Reloads the image of the {@link ChessBoard} at its current state.       */
    public void reloadImage() {
        if( files[indexImage % files.length].exists() )
            System.out.println("The file " + files[indexImage % files.length].getName() + " exists");
        else System.out.println("The file " + files[indexImage % files.length].getName() + " doesnt exists");

        // Reload the image - resized
        BufferedImage buffer = null;
        try {
            buffer = ImageIO.read( files[indexImage % files.length] );
            } catch (IOException e) {           e.printStackTrace();        }
        Image rescaledImage = buffer.getScaledInstance(imageResolution, imageResolution, Image.SCALE_SMOOTH);
        icon = new ImageIcon(rescaledImage);

        boardImage = new JLabel(icon);
    //  boardImage.setText( files[indexImage % files.length].getName() );

        System.out.println("Is now showing " + files[indexImage % files.length].getName() );

        boardImage.repaint();
    }


    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    Test frame = new Test();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

}

Answer 1

In reality, no image is shown.

boardImage = new JLabel(icon);

不要创建新的 JLabel。该 JLabel 的实例尚未添加到框架中。

只需更改现有 JLabel 的图标即可：

//boardImage = new JLabel(icon);
boardImage.setIcon( icon );

标签将自动使用新图标重绘自身。

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