无法让我的面板另存为图像

Question

我做了一个简单的画图程序，但似乎有一些问题。首先，当我运行程序时，组件不会显示，直到我将鼠标拖到每个组件上。其次，我创建的 drawPanel 图像仅保存面板的背景，而不保存其上绘制的内容。另一个小问题是，当我通过下拉菜单更改点的大小时，在它下面绘制的任何内容都会被删除。任何关于清理我的代码或解决我的问题的建议都会很棒。

import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

public class MyPaint extends JFrame implements MouseListener, MouseMotionListener, ActionListener {

//initialize coordinates somewhere offscreen
int myX = -100, myY = -100;
private JPanel bucket = new JPanel(new GridLayout(7, 2));
private JPanel northPanel = new JPanel(new GridBagLayout());
private JPanel drawPanel = new JPanel();
GridBagConstraints c = new GridBagConstraints();
private String[] pencilSize = {"1", "5", "10", "15", "20"};
private JComboBox sizeList = new JComboBox(pencilSize);
private JButton[] buttons = new JButton[11];
private Color[] colorList = {Color.RED, Color.BLUE, Color.ORANGE, Color.CYAN, Color.YELLOW, Color.GREEN, 
                             Color.WHITE, Color.MAGENTA, Color.GRAY, Color.PINK, Color.BLACK};
private Color currentColor = Color.BLACK;
int radius = 5;
private JLabel thickness = new JLabel("Thickness");
private JButton clear = new JButton("Clear");
private JButton save = new JButton("Save");
private JButton open = new JButton("Open");
private JLabel image = new JLabel(" ");
JFileChooser fc = new JFileChooser();

// *******************  MyPaint **************

public MyPaint(){
    super("MyPaint");
    setSize(1000, 1000);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    addMouseListener(this);
    addMouseMotionListener(this);
    setVisible(true);
    setResizable(false);
    sizeList.setEditable(true);
    drawPanel.setBorder(BorderFactory.createLineBorder(Color.BLACK));

    for(int i = 0; i < buttons.length; i++){
        buttons[i] = new JButton();
        buttons[i].setBackground(colorList[i]);
        buttons[i].addActionListener(this);
        bucket.add(buttons[i]);
    }

    northPanel.add(clear);
    clear.addActionListener(this);
    northPanel.add(thickness);
    northPanel.add(sizeList);
    sizeList.addActionListener(this);
    northPanel.add(open);
    open.addActionListener(this);
    northPanel.add(save);
    save.addActionListener(this);

    add(drawPanel, BorderLayout.CENTER);
    add(bucket, BorderLayout.WEST);
    add(northPanel, BorderLayout.NORTH);
}

// *******************  Override of paint **************

//paint the oval at the current location
public void paint(Graphics g){
    g.setColor(currentColor);
    if(myX > drawPanel.getX() + 10 && myY > drawPanel.getY() + 25)
        g.fillOval(myX - radius, myY - radius, 2 * radius, 2 * radius);
}

// *******************  Mouse Events **************

public void mouseClicked(MouseEvent e){
    myX = e.getX();
    myY = e.getY();
    repaint();
}

public void mouseEntered(MouseEvent e) {
}
public void mouseExited(MouseEvent e) {
}
public void mousePressed(MouseEvent e) {
}
public void mouseReleased(MouseEvent e) {
}

public void mouseDragged(MouseEvent e){
    myX = e.getX();
    myY = e.getY();
    repaint();
}

public void mouseMoved(MouseEvent e){

}

// *******************  Actions **************

public void actionPerformed(ActionEvent e) {
    Object source = e.getSource();
    for(int i = 0; i < buttons.length; i++)
        if(source == buttons[i])
            currentColor = colorList[i];

    if(source == clear)
        super.paint(getGraphics());

    else if(source == sizeList)
        radius = Integer.parseInt((String) sizeList.getSelectedItem());

    //open a file
    else if(source == open){
         int returnValue = fc.showOpenDialog(null);
            if (returnValue == fc.APPROVE_OPTION) {
              File sf = fc.getSelectedFile();
              try {
                image.setIcon(new ImageIcon(ImageIO.read(sf)));
            } catch (IOException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
              super.paint(getGraphics());
              drawPanel.add(image);
              drawPanel.revalidate();
              drawPanel.repaint();
            }
    }

    //save a file
    else if(source == save){
        fc.setDialogTitle("Specify a file to save");   

        int userSelection = fc.showSaveDialog(drawPanel);

        if (userSelection == JFileChooser.APPROVE_OPTION) {
            File fileToSave = fc.getSelectedFile();
            try{
                BufferedImage image = new BufferedImage(drawPanel.getWidth(),
                        drawPanel.getHeight(), BufferedImage.TYPE_4BYTE_ABGR);
                Graphics g = image.getGraphics();
                drawPanel.printAll(g);
                g.dispose();
                ImageIO.write(image, "png", new File("pic.png"));
            } catch (Exception e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
        }

    }
}

// *******************  Main **************

public static void main(String[] args){
    MyPaint frame = new MyPaint();
    frame.setVisible(true);
}


}

编辑：

我用 paintComponent() 替换了 paint() 但我仍然不知道如何在上面绘图，因为 g.fillOval...() 什么都不做

public void paintComponent(Graphics g) {
    super.paintComponents(g);
    g.setColor(currentColor);
    g.fillOval(myX - radius, myY - radius, 2 * radius, 2 * radius);
    if(img != null)
        g.drawImage(img, 0, 0, null);
}

编辑 2：

小版

import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

public class MySmallPaint extends JPanel implements MouseListener, MouseMotionListener, ActionListener{

int myX = 0, myY = 0;
int radius = 5;
JPanel drawPanel = new JPanel();
Dimension d = drawPanel.getPreferredSize();
BufferedImage img = new BufferedImage(d.width,d.height, BufferedImage.TYPE_INT_RGB);
Graphics2D g = img.createGraphics();

public MySmallPaint(){
    super();
    setSize(1000, 1000);
    addMouseListener(this);
    addMouseMotionListener(this);
    //add(drawPanel, BorderLayout.CENTER);
}

public void paintComponent(Graphics g) {
    super.paintComponents(g);
    g.fillOval(myX - radius, myY - radius, 2 * radius, 2 * radius);
    if(img != null)
        g.drawImage(img, 0, 0, null);
}

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

@Override
public void mouseDragged(MouseEvent e) {
    // TODO Auto-generated method stub
    myX = e.getX();
    myY = e.getY();
    repaint();
}

@Override
public void mouseMoved(MouseEvent arg0) {
    // TODO Auto-generated method stub
}

@Override
public void mouseClicked(MouseEvent e) {
    myX = e.getX();
    myY = e.getY();
    repaint();
}

@Override
public void mouseEntered(MouseEvent arg0) {
    // TODO Auto-generated method stub
}

@Override
public void mouseExited(MouseEvent arg0) {
    // TODO Auto-generated method stub
}

@Override
public void mousePressed(MouseEvent arg0) {
    // TODO Auto-generated method stub
}

@Override
public void mouseReleased(MouseEvent arg0) {
    // TODO Auto-generated method stub
}

public static void main(String[] args){
     JFrame f = new JFrame("Swing Paint Demo");
     f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     f.add(new MySmallPaint());
     f.pack();
     f.setVisible(true);
}
}

Answer 1

解决了一个问题：

您没有在您的 paint 方法覆盖中调用 super 的 paint 方法，这样做不允许 GUI 绘制它自己的组件。换句话说，你没有这样做：

public void paint(Graphics g) {
   super.paint(g);  // *************** missing ************
   g.setColor(currentColor);
   if (myX > drawPanel.getX() + 10 && myY > drawPanel.getY() + 25)
      g.fillOval(myX - radius, myY - radius, 2 * radius, 2 * radius);
}

但话虽如此，我也强烈建议您不要像现在这样绘制，而是重写 JPanel 的 paintComponent 方法并在其中绘制。通过直接在 JFrame 上绘制，您可能会弄乱它如何绘制自身、组件、边框……正如您所发现的那样。 JFrames 是复杂的组件，包含许多子组件，包括 JRootPanes、contentPanes、JLayeredPanes、glasspanes 等，您真的不想冒险弄乱这些子组件的绘制。

接下来，要将图像保存在绘图中，绘制到 BufferedImage，然后在绘图 JPanel（附加了 MouseListener 的）paintComponent 中显示该 BufferedImage，例如：

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    if (myImage != null) {
        g.drawImage(myImage, 0, 0, null);
    }
}

因此，在您的鼠标侦听器中，您使用从图像上调用 getGraphics() 或 createGraphics() 获得的 Graphics 绘制此图像。前者获取一个 Graphics 对象，而后者获取一个 Graphics2D 对象。请注意，这与在 不推荐 的组件上调用 getGraphics() 不同（根据我的评论）。另请注意，以这种方式获得的任何 Graphics 对象都应在您使用完后丢弃，以免浪费资源。

I created a BufferedImage but how do I add it to my drawPanel / JFrame.

您的绘图 JPanel 可以将 BufferedImage 作为字段保存。当您需要在其上绘图时，您会获得其 Graphics 上下文，如上文所述——请注意，我更喜欢使用 createGraphics() 来获取 Graphics2D 对象，这样我就可以使用它的所有好东西，例如 Strokes。您将 BufferedImage 调整为您的 JPanel 的首选大小，然后按照我在上面显示的方式绘制它。

I am also unsure as how to draw on the buffered image.

如上所述。另请注意，如果您尝试创建连接图，通常最好绘制直线而不是椭圆形或椭圆形

举个简单的例子，一个没有你想要做的所有事情的例子......

import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Stroke;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.image.BufferedImage;

import javax.swing.AbstractAction;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

@SuppressWarnings("serial")
public class SimpleDrawMain extends JPanel {
   private static final int PREF_W = 600;
   private static final int PREF_H = PREF_W;
   private SimpleDrawPanel simpleDrawPanel = new SimpleDrawPanel(PREF_W, PREF_H);
   private MyMouse myMouse = new MyMouse();

   // drawStroke: thickness of lines drawn. Can change this as needed
   private Stroke drawStroke = new BasicStroke(6f);
   // drawColor -- change this as needed
   private Color drawColor = Color.BLUE; 

   public SimpleDrawMain() {
      simpleDrawPanel.addMouseListener(myMouse);
      simpleDrawPanel.addMouseMotionListener(myMouse);
      simpleDrawPanel.setBorder(BorderFactory.createLineBorder(Color.DARK_GRAY));

      JPanel topPanel = new JPanel();
      topPanel.add(new JButton(new SaveImageAction("Save", KeyEvent.VK_S)));
      topPanel.add(new JButton(new ClearImageAction("Clear", KeyEvent.VK_C)));

      setLayout(new BorderLayout());
      add(topPanel, BorderLayout.PAGE_START);
      add(simpleDrawPanel, BorderLayout.CENTER);
   }

   private class MyMouse extends MouseAdapter {
      private Graphics2D g2;
      private Point point; // point to draw a line with

      @Override
      public void mousePressed(MouseEvent e) {
         if (e.getButton() != MouseEvent.BUTTON1) {
            return;
         }

         // get our Graphics object to draw with
         g2 = simpleDrawPanel.getMyImage().createGraphics();
         point = e.getPoint();  // get the first point
         g2.setStroke(drawStroke);  // set stroke and color
         g2.setColor(drawColor);
      }

      @Override
      public void mouseDragged(MouseEvent e) {
         if (point == null) {
            return;
         }
         drawOnImage(e);
      }

      @Override
      public void mouseReleased(MouseEvent e) {
         if (point == null) {
            return;
         }
         drawOnImage(e);

         // clean up things
         g2.dispose();
         g2 = null;
         point = null;
      }

      private void drawOnImage(MouseEvent e) {
         // better to draw a line between two points rather than an oval
         // get 2nd point, and then using 2 points, create line to draw
         Point p2 = e.getPoint();
         int x1 = point.x;
         int y1 = point.y;
         int x2 = p2.x;
         int y2 = p2.y;
         g2.drawLine(x1, y1, x2, y2);

         // reset the original point to the new point
         point = p2;

         simpleDrawPanel.repaint();
      }

   }

   private class SaveImageAction extends AbstractAction {
      public SaveImageAction(String name, int mnemonioc) {
         super(name);
         putValue(MNEMONIC_KEY, mnemonioc);
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         BufferedImage img = simpleDrawPanel.getMyImage();
         // TODO write code to save img to file         
      }
   }

   private class ClearImageAction extends AbstractAction {
      public ClearImageAction(String name, int mnemonioc) {
         super(name);
         putValue(MNEMONIC_KEY, mnemonioc);
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         simpleDrawPanel.clearImage();
      }
   }

   private static void createAndShowGui() {
      SimpleDrawMain mainPanel = new SimpleDrawMain();

      JFrame frame = new JFrame("SimpleDraw");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setResizable(false);
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

class SimpleDrawPanel extends JPanel {
   // preferred size dimensions for this JPanel
   private int prefW;
   private int prefH;
   // image to draw on
   private BufferedImage myImage;

   public SimpleDrawPanel(int prefW, int prefH) {
      this.prefW = prefW;
      this.prefH = prefH;
      myImage = new BufferedImage(prefW, prefH, BufferedImage.TYPE_INT_ARGB);
   }

   public BufferedImage getMyImage() {
      return myImage;            
   }

   public void clearImage() {
      // simply create a new BufferedImage
      myImage = new BufferedImage(prefW, prefH, BufferedImage.TYPE_INT_ARGB);
      repaint();
   }

   @Override
   public Dimension getPreferredSize() {
      if (isPreferredSizeSet()) {
         return super.getPreferredSize();
      }
      return new Dimension(prefW, prefH);
   }

   @Override
   protected void paintComponent(Graphics g) {
       super.paintComponent(g);
       if (myImage != null) {
           g.drawImage(myImage, 0, 0, null);
       }
   }

}

无法让我的面板另存为图像

Can't get my panel to save as an image

java

swing

bufferedimage

jpanel

jframe