如何在框架中显示图像？

Question

我正在编写一个gui,我想使用嵌入一些图片,但在将它嵌入我的主程序之前,我编写了该代码来测试它:

    public class guikopie extends javax.swing.JFrame{
        public guikopie() {
            a = new javax.swing.JLabel();
            setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
            a.setIcon(new javax.swing.ImageIcon("C:\\Users\\Public\\Pictures\\Sample Pictures\\Tulpen.jpg"));       
            add(a);//here i add it to the jlabel
            pack();
        }

        public static void main(String args[]){
            java.awt.EventQueue.invokeLater(new Runnable() {
                public void run() {
                    new guikopie().setVisible(true);
                }
            });
        }

        private javax.swing.JLabel a;
    }

我的问题是:为什么这段代码不显示图片？

Answer 1

我想人们可能会因为重复这个而讨厌我:P:

• 不要扩展JFrame类
• 类名以首字母开头即 Guikopie

还取决于背景的用途,即如果它的徽标将被添加到JPanel当时使用a 的特定位置JLabel是好的,但是,如果它被用作背景则不是; 因为它会随着更多组件的添加而移动,因此我们不应该将背景添加为组件而是在组件上绘制背景.

至于你的问题:

我的问题是:为什么这段代码不显示图片？

您的代码对我来说非常合适,因此您的图片位置必须不正确.

我没有展示如何将添加一个简单的例子Image来JPanel的背景,然后添加JPanel到JFrame,还包括类ImgUtils调整大小的图片:

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.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class JFrameWithPicture {

    public JFrameWithPicture() throws MalformedURLException, IOException {
        initComponents();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    new JFrameWithPicture();
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            }
        });
    }

    private void initComponents() throws MalformedURLException, IOException {
        JFrame frame = new JFrame("Frame with JPanel and background");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        final Image background = ImageUtils.scaleImage(300, 300, ImageIO.read(new URL("http://images2.layoutsparks.com/1/98191/naruto-14-red-design.jpg")));
        final Dimension jpanelDimensions = new Dimension(new ImageIcon(background).getIconWidth(), new ImageIcon(background).getIconHeight());

        frame.add(new JPanel() {
            @Override
            protected void paintComponent(Graphics grphcs) {
                super.paintComponent(grphcs);
                grphcs.drawImage(background, 0, 0, this);
            }

            @Override
            public Dimension getPreferredSize() {
                return jpanelDimensions;
            }
        });

        frame.setResizable(false);
        frame.pack();
        frame.setVisible(true);
    }
}

class ImageUtils {

    public static BufferedImage scaleImage(int width, int height, String filename) {
        BufferedImage bi;
        try {
            ImageIcon ii = new ImageIcon(filename);
            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(ii.getImage(), 0, 0, width, height, null);
        } catch (Exception e) {
            return null;
        }
        return bi;
    }

    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;
    }
}

或者你可能想要使用Image#getScaledInstance(int width,int height,int hints)调整大小,但这有其危险,主要问题是:

Image.getScaledInstance()不会返回完成的缩放图像.当使用图像像素时,它将大部分缩放工作留在以后的时间.