如何正确刷新JFrame中的图像?

我个人而言，可以在将其应用于标签之前调整其大小，也可以使用JPanel进行绘画. JLabel具有很多功能.

Personally, I would either resize it before applying it to the label or use a JPanel to perform the painting. JLabel has to much functionality dragging around with it.

举例来说，您遇到的问题是您实际上是在使用setIcon设置图像，但是使用paintComponent在其顶部绘制另一个(初始)图像

Case in point, the problem you're having is you're actually using setIcon to set the image, but using paintComponent to paint another (the initial) image over the top of it

您的自定义标签将ImageIcon作为初始参数并将其绘制为这样...

Your custom label takes a ImageIcon as a inital parameter and paints it as such...

private static class MyJLabel extends JLabel {
    private ImageIcon img = null;

    public MyJLabel(ImageIcon img) {
        super();
        this.img = img;
    }

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

您可以这样初始化它...

You initialise it as such...

label = new MyJLabel(new ImageIcon(img));

应注意，如果使用JLabel的Icon支持，则此...

It should be noted that if you used the Icon support of JLabel, this...

label.setPreferredSize(dims);

无关紧要，因为JLabel会使用图标大小来确定其首选大小...但是无论如何...

Would be irrelevant as the JLabel would use the icon size to determine it's preferred size...but any way...

然后使用此图标更新图标.

Then you update the icon using this..

img = image;
if (label != null) {
    label.setIcon(new ImageIcon(img));
    label.repaint();
}

应该指出的是，根据您的示例，这实际上是在EDT之外被调用的，这很危险，并且可能导致油漆变脏

但是setIcon永远不会更改MyLabel中img的值，因此，当调用paintComponent方法时，实际上是在更新中提供的图标上绘画...

But setIcon never changes the value of img within MyLabel, so when your paintComponent method is called, you are actually painting over the icon you have supplied in the update...

// Paint the new Icon
super.paintComponent(g);
// Paint the old/initial image...
g.drawImage(img.getImage(), 0, 0, getWidth(), getHeight(), this);

已更新

个人而言，我要做的是使用JPanel之类的东西创建一个自定义组件，并根据面板的当前大小缩放原始图像，例如...

Personally, what I would do is create a custom component, using something like a JPanel and scale the original image based on the current size of the panel, for example...

现在，通常在执行图像缩放时，我更喜欢使用分而治之的方法，如

Now, normally, when performing image scaling I prefer to use a divide and conqure approach as demonstrated in Java: maintaining aspect ratio of JPanel background image, but for this example, I've simply used and AffineTransform for simplicity sake

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.HeadlessException;
import java.awt.Image;
import java.awt.geom.AffineTransform;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class ScalableImageExample {

    public static void main(String[] args) {
        new ScalableImageExample();
    }

    public ScalableImageExample() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                try {
                    ResizableImagePane pane = new ResizableImagePane();
                    pane.setImage(...);

                    JFrame frame = new JFrame("Testing");
                    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                    frame.add(pane);
                    frame.pack();
                    frame.setLocationRelativeTo(null);
                    frame.setVisible(true);
                } catch (IOException exp) {
                    exp.printStackTrace();
                }
            }
        });
    }

    public class ResizableImagePane extends JPanel {

        private Image img;

        public ResizableImagePane() {
        }

        public void setImage(Image value) {
            if (img != value) {
                Image old = img;
                this.img = value;
                firePropertyChange("image", old, img);
                revalidate();
                repaint();
            }
        }

        public Image getImage() {
            return img;
        }

        @Override
        public Dimension getPreferredSize() {
            return img == null ? new Dimension(200, 200) : new Dimension(img.getWidth(this), img.getHeight(this));
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            if (img != null) {
                Graphics2D g2d = (Graphics2D) g.create();

                int width = getWidth();
                int height = getHeight();

                double scaleFactor = getScaleFactorToFit(new Dimension(img.getWidth(this), img.getHeight(this)), getSize());

                int x = (int)((width - (img.getWidth(this) * scaleFactor)) / 2);
                int y = (int)((height - (img.getHeight(this) * scaleFactor)) / 2);

                AffineTransform at = new AffineTransform();
                at.translate(x, y);
                at.scale(scaleFactor, scaleFactor);
                g2d.setTransform(at);
                g2d.drawImage(img, 0, 0, this);
                g2d.dispose();
            }
        }

        public double getScaleFactor(int iMasterSize, int iTargetSize) {

            return (double) iTargetSize / (double) iMasterSize;

        }

        public double getScaleFactorToFit(Dimension original, Dimension toFit) {

            double dScale = 1d;

            if (original != null && toFit != null) {

                double dScaleWidth = getScaleFactor(original.width, toFit.width);
                double dScaleHeight = getScaleFactor(original.height, toFit.height);

                dScale = Math.min(dScaleHeight, dScaleWidth);

            }

            return dScale;

        }

    }

}