圖像繪圖適用於JFrame，但不適用於JPanel

Question

我正在通過一些簡單的應用程序來熟悉Swing並遇到問題。

我正在嘗試一個包含圖像的面板（在面板中）以及用於放大/縮小圖像的按鈕。

我已經能夠使添加了圖像的框架正常工作（盡管存在一些框架大小問題，但這是另一個故事），但是，當我調用相同的組件類將其添加到面板中時，什么也沒出現。 我希望你們中的一員可以幫助您了解情況。

碼：

鏡框-如圖所示工作

class ImageFrame extends JFrame{

public ImageFrame(){
    setTitle("Java Image Machine");

    init();
    pack();
}   

public final void init(){
    //ZoomPanel zoomPanel = new ZoomPanel();
    //ImagePanel imagePanel = new ImagePanel();
    ImageComponent component = new ImageComponent();

    //this.add(zoomPanel, BorderLayout.CENTER);
    this.add(component);
    //this.add(imagePanel, BorderLayout.SOUTH);
}
}

但是，在直接調用ImageComponent的同時使用ImagePanel或添加ZoomPanel不會：

class ImagePanel extends JPanel{    
public ImagePanel(){
    //setBorder(BorderFactory.createLineBorder(Color.black));
    ImageComponent component = new ImageComponent();
    add(component);
}   
}

組件類：

class ImageComponent extends JComponent{
public ImageComponent(){

    try{
        image = ImageIO.read(new File("test1.bmp"));
    }
    catch ( IOException e ){
        e.printStackTrace();
    }

    System.out.println("W: " + image.getWidth(this) + " H: " + image.getHeight(this));
}

public void paintComponent( Graphics g ){
    super.paintComponent(g);
    if (image == null)
        return;

    width = image.getWidth(this);
    height = image.getHeight(this);

    //System.out.println("Image should be painted");
    g.drawImage(image, 0, 0, null);
}

private Image image;
public int width;
public int height;

}

Answer 1

它對我來說很好（我剛剛測試了ImageComponent類）：

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JComponent;
import javax.swing.JFrame;

public class Test {

    /**
     * Default constructor Test.class
     */
    public Test() {
        initComponents();
    }

    public static void main(String[] args) {

        /**
         * Create GUI and components on Event-Dispatch-Thread
         */
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                Test test = new Test();
            }
        });
    }

    /**
     * Initialize GUI and components (including ActionListeners etc)
     */
    private void initComponents() {
        JFrame jFrame = new JFrame();
        jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //add ImageComponent to JFrame instance
        jFrame.add(new ImageComponent());

        //pack frame (size JFrame to match preferred sizes of added components and set visible
        jFrame.pack();
        jFrame.setVisible(true);
    }
}

class ImageComponent extends JComponent {

    private Image image;
    public int width;
    public int height;

    public ImageComponent() {
        try {
            image = ImageUtils.scaleImage(300, 300, ImageIO.read(new URL("http://harmful.cat-v.org/software/_java/java-evil-edition.png")));
            //image =  ImageIO.read(new URL("http://harmful.cat-v.org/software/_java/java-evil-edition.png"));//uses images scale
        } catch (Exception e) {
            e.printStackTrace();
        }

        //so we can set the JPanel preferred size to the image width and height
        ImageIcon ii = new ImageIcon(image);
        width = ii.getIconWidth();
        height = ii.getIconHeight();
    }

    //so our panel is the same size as image
    @Override
    public Dimension getPreferredSize() {
        return new Dimension(width, height);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);

        if (image == null) {
            return;
        }

        width = image.getWidth(this);
        height = image.getHeight(this);

        g.drawImage(image, 0, 0, null);
    }
}
//class used for scaling images
class ImageUtils {

    static Image scaleImage(int width, int height, BufferedImage filename) {
        BufferedImage bi;
        try {
            bi = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
            Graphics2D g2d = (Graphics2D) bi.createGraphics();
            g2d.addRenderingHints(new RenderingHints(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY));
            g2d.drawImage(filename, 0, 0, width, height, null);
        } catch (Exception e) {
            return null;
        }
        return bi;
    }
}

問題可能是文件的路徑，或者JPanel寬度和高度與圖片不同，因此我們重寫了JPanel getPrefferedSize(...) ，並根據Image返回正確的大小。

Answer 2

在添加適當的組件之后，您是否嘗試過添加repaint()調用？

即

class ImagePanel extends JPanel{    
    public ImagePanel(){
        //setBorder(BorderFactory.createLineBorder(Color.black));
        ImageComponent component = new ImageComponent();
        add(component);
        repaint();
    }   
}

還要仔細檢查您是否正在將ImagePanel（包含ImageComponent）添加到ImageFrame，並調用.setVisible（True）。