Question

我有一个JPanel（imagePanel），上面有一个图像。我将imagePanel放在另一个JPanel（scrollPanel）里面，用GridBagLayout默认约束来居中它。 scrollPanel是JScrollPane的视口。我需要在事后更改imagePanel的大小并仍然保持居中。（图像类是我自己制作的一个）

public class ImageView extends View {
private static final long serialVersionUID = -1745026846891845769L;

private JScrollPane scrollPane;
private JPanel scrollPanel;
public JPanel imagePanel;

public int zoom = 1;

public Image image;

public ImageView(Image image) {
    setLayout(new BorderLayout());
    setDoubleBuffered(true);

    this.image = image;

    imagePanel = new JPanel() {
        private static final long serialVersionUID = 2127374649591395224L;

        @Override
        public void paint(Graphics g) {
            super.paint(g);
            ImageView.this.image.paintImage(g, 0, 0, zoom);
        }
    };
    imagePanel.setDoubleBuffered(true);

    scrollPanel = new JPanel(new GridBagLayout());
    scrollPanel.add(imagePanel);

    scrollPane = new JScrollPane(scrollPanel);
    add(scrollPane, BorderLayout.CENTER);
}

public void zoom(int zoom) {
    if(zoom < 1) 
        this.zoom = 1;
    else
        this.zoom = zoom;

    int imageWidth = image.WIDTH * this.zoom;
    int imageHeight = image.HEIGHT * this.zoom;

    imagePanel.setPreferredSize(new Dimension(imageWidth, imageHeight));
    //What do I do here???
}

编辑：这是我为其他任何有相同问题的人更新的代码

public class ImageView extends View {
private static final long serialVersionUID = -1745026846891845769L;

public class ImagePanel extends JPanel {
    private static final long serialVersionUID = 2127374649591395224L;

    public int zoom = 1;

    public void setZoom(int zoom) {
        if(zoom < 1) 
            this.zoom = 1;
        else
            this.zoom = zoom;
    }

    @Override
    public Dimension getPreferredSize() {
        int imageWidth = ImageView.this.image.WIDTH * this.zoom;
        int imageHeight = ImageView.this.image.HEIGHT * this.zoom;
        return new Dimension(imageWidth, imageHeight);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        ImageView.this.image.paintImage(g, 0, 0, zoom);
    }

}

private JScrollPane scrollPane;
private JPanel scrollPanel;
public ImagePanel imagePanel;

public Image image;

public ImageView(Image image) {
    setLayout(new BorderLayout());
    setDoubleBuffered(true);

    this.image = image;

    imagePanel = new ImagePanel();
    imagePanel.setDoubleBuffered(true);

    scrollPanel = new JPanel(new GridBagLayout());
    scrollPanel.add(imagePanel);

    scrollPane = new JScrollPane(scrollPanel);
    add(scrollPane, BorderLayout.CENTER);
}

public void zoom(int zoom) {
    imagePanel.setZoom(zoom);
    scrollPanel.revalidate();
    scrollPanel.repaint();
}

Answer 1

不要调用setPreferredSize（）。

您应该覆盖类的getPreferredSize()方法来进行大小计算。所以基本上应该在该方法中定义缩放逻辑。

然后在zoom（..）方法中调用：

revalidate();
repaint();

zoom()方法应该是绘制图像的面板的一部分，因为缩放系数是此面板的属性。这将导致调用布局管理器，并且将在组件的布局中使用新的首选大小。

此外，您应该覆盖paintComponent(...)方法，而不是paint（...）方法来绘制图像。

Answer 2

根据此链接：http://www.coderanch.com/t/333435/GUI/java/Whats-exact-difference-paint-repaint 调用setPreferedSize

后，您可能需要调用validate

事实之后setPreferredSize发生了变化，但GridBagLayout没有更新

2 个答案: