Question

我是jave的新手，我的第一个项目是绘制，并从JPanel保存图像，我的绘图已经完成，但是在我绘制JPanel之后我无法保存它:(，那么你可以帮我修复它吗当我在绘制后打开图像时，它不包含任何东西:( 在这里我的代码：

package image;
import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Graphics;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.nio.file.Path;
import javax.imageio.ImageIO;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;


public class paint extends JFrame{
private Point points[] = new Point[10000];
private Point pointends[] = new Point[10000];
private int pointCount = 0;
private JButton save_btn;
public paint()
{
    panel paint2 = new panel();
    add(paint2,BorderLayout.CENTER);
}
private class panel extends JPanel
{   
    private paint my_paint;
    public panel()
    {   
        setBackground(Color.WHITE);
        save_btn = new JButton();
        save_btn.setText("123");
        this.add(save_btn);
        ButtonHandler handler1 = new ButtonHandler();
        save_btn.addActionListener(handler1);
        MouseHandler handler = new MouseHandler();
        this.addMouseMotionListener(handler);

        this.addMouseListener(handler);
    }
    private class ButtonHandler implements ActionListener
    {

        @Override
        public void actionPerformed(ActionEvent arg0) {
            // TODO Auto-generated method stub
            savefile();
        }

    }
    @Override
    protected void paintComponent(Graphics g) 
    {
        // TODO Auto-generated method stub
        super.paintComponent(g);
        for(int i = 0;i <pointCount;i++)
        {   
            g.setColor(Color.RED);
            g.drawLine(points[i].x, points[i].y, pointends[i].x, pointends[i].y);
        }           
    }



private class MouseHandler extends MouseAdapter
{  
    @Override
    public void mouseDragged(MouseEvent e) 
    {
        // TODO Auto-generated method stub
            pointends[ pointCount-1] = e.getPoint();
            repaint();


    }
    @Override
    public void mousePressed(MouseEvent e) {
        // TODO Auto-generated method stub
        super.mousePressed(e);
        if(pointCount < points.length)
        {
            points[ pointCount ] = e.getPoint();
            pointends[ pointCount ] = e.getPoint();
            pointCount++; 
            repaint();
        }
    }
    @Override
    public void mouseReleased(MouseEvent e) {
        // TODO Auto-generated method stub
        super.mouseReleased(e);
        /*pointends[pointCount]=e.getPoint();
        repaint();
        pointCount++;
    */
    }

    }

}
public void savefile()
{
    BufferedImage image2 = new BufferedImage(panel.WIDTH, panel.HEIGHT,     BufferedImage.TYPE_INT_RGB);
    JFileChooser jFile = new JFileChooser();
    jFile.showSaveDialog(null);
    Path pth = jFile.getSelectedFile().toPath();
    JOptionPane.showMessageDialog(null, pth.toString());
    Graphics2D graphics2D = image2.createGraphics();
    try {
        ImageIO.write(image2, "", new File(pth.toString()));
    } catch (IOException ox) {
        // TODO: handle exception
        ox.printStackTrace();

}
}
}

Answer 1

创建BufferedImage以存储您的绘画。在绘画时，在BufferedImage上绘画。

当你需要在JPanel上显示绘画时，在JPanel上绘制BufferedImage。

这样，您可以将绘画加载/保存到文件中。

这样的事情：

import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JPanel;

public class Paint extends JPanel{
    private BufferedImage paintImage = new BufferedImage(500, 400, BufferedImage.TYPE_3BYTE_BGR);

    @Override
    protected void paintComponent(Graphics g){
        super.paintComponent(g);
        g.drawImage(paintImage, 0, 0, null);
    }

    // draw painting
    public void updatePaint(){
        Graphics g = paintImage.createGraphics();

        // draw on paintImage using Graphics

        g.dispose();
        // repaint panel with new modified paint
        repaint();
    }

    public void save() throws IOException{
        ImageIO.write(paintImage, "PNG", new File("filename.png"));
    }

    public void load() throws IOException {
        paintImage = ImageIO.read(new File("filename.png"));
        // update panel with new paint image
        repaint();
    }
}

Answer 2

有一个很好的方法：

BufferedImage image = new BufferedImage(component.getWidth(), component.getHeight(), BufferedImage.TYPE_INT_ARGB);
Graphics g = image.getGraphics();
component.paint(g);
 try {
        ImageIO.write(image, "png", new File(filename));
    } catch (IOException ex) {
        Logger.getLogger(CustomApp.class.getName()).log(Level.SEVERE, null, ex);
   }

它所做的一切：它创建一个具有可见组件大小和ARGB类型的图像，以获得透明度支持。然后它获取图形并将其传递给我们想要快照的组件。它描绘了该组件的子组件，包括在其上绘制的任何内容。

更新：您也可以使用component.print（Graphics g）：

Dimension componentSize = component.getPreferredSize();
component.setSize(componentSize); // need to make sure that both sizes are equal
BufferedImage image = new BufferedImage(comonent.getWidth(), component.getHeight(), BufferedImage.TYPE_INT_RGB);
Graphics g = image.createGraphics();
g.fillRect(0, 0, image.getWidth(), image.getHeight());
component.print(g);

但是这个函数只会绘制组件的渲染图形，而不会绘制子组件。我测试了它。

修改

您的paint extends JFrame课程名称可以很好，例如PaintFrame extends JFrame。类名不应该具有函数的名称，paint是verb，它是函数。

panel extends JPanel：我们为什么要选择带小写首字母的班级名称呢？我们可以给出我们的组件名称以反映我们正在使用它做什么：比如，我们正在绘制如此MyCanvas extends JPanel

在panel您的第一个陈述private paint my_paint;内：不必要地在这做什么？

您的saveFile()函数属于JFrame，并且您已在框架构造函数的本地创建了panel（您正在绘制的函数）。 saveFile()函数应如何访问它？在JFrame类上下文中将您的绘图面板声明为public或private。

我用有意义的方式撰写了使用getWidth()和getHeight()来阅读组件的大小但是你写的是：

BufferedImage image2 = new BufferedImage(panel.WIDTH, panel.HEIGHT, ...);

我再次完全编写了代码，如何使用png函数将图像保存为ImageIO.write(image, "png", "myFile.png")。 请仔细阅读答案。

以下资源可能会有所帮助：

A closer look at painting mechanism.

Writing and saving images

Answer 3

private void saveImage(){
    BufferedImage imagebuf=null;
    try {
        imagebuf = new Robot().createScreenCapture(panel.bounds());
    } catch (AWTException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }  
     Graphics2D graphics2D = imagebuf.createGraphics();
     panel.paint(graphics2D);
     try {
        ImageIO.write(imagebuf,"jpeg", new File("save1.jpeg"));
    } catch (Exception e) {
        // TODO Auto-generated catch block
        System.out.println("error");
    }
}

result example of snippet code

Answer 4

Screen Image允许您保存任何组件的图像。

绘制后从JPanel保存图像

4 个答案: