对JPanel使用addMouseListener()和paintComponent()

This is a follow-up to my previous question. I've simplified things as much as I could, and it still doesn't work! Although the good thing I got around using getGraphics().

这是我之前问题的后续。我尽可能地简化了事情，但它仍然不起作用!尽管使用getGraphics()是件好事。

A detailed explanation on what goes wrong here is massively appreciated. My suspicion is that something's wrong with the the way I used addMouseListener() method here.

对于这里出现的问题，我们非常感激。我怀疑我使用addMouseListener()方法的方式有问题。

EDIT completely rewrote the code. Still does not work properly though.

编辑完全重写代码。但仍然不能正常工作。

import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;

import javax.swing.JFrame;
import javax.swing.JPanel;


public class RunClass{

    static MainClass1 inst1 = new MainClass1();



    public static void main(String args[]){

        JFrame frame1 = new JFrame();
        frame1.add(inst1);
        frame1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame1.setTitle("NewPaintToolbox");
        frame1.setSize(200, 200);
        frame1.setLocationRelativeTo(null);     
        frame1.setVisible(true);                
    }
}

class MainClass1 extends JPanel implements MouseListener, MouseMotionListener{

    int xvar=30;
    int yvar=30;
    //static PaintClass22 inst1 = new PaintClass22();


    @Override
    public void mouseClicked(MouseEvent arg0) {
        // TODO Auto-generated method stub
        xvar = arg0.getX();
        yvar = arg0.getY();
        repaint(xvar,yvar,10,10);

    }   

    @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 e) {
        // TODO Auto-generated method stub

    }

    @Override
    public void mouseDragged(MouseEvent arg0) {
        // TODO Auto-generated method stub
        xvar = arg0.getX();
        yvar = arg0.getY();
        repaint(xvar,yvar,10,10);

    }

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

    }
    @Override
    public void paintComponent(Graphics g){

        super.paintComponent(g);
        g.setColor(Color.RED);
        g.fillRect(xvar, yvar, 10, 10);     

    }



}

4 个解决方案

#1

You must add the mouseListener to the panel. That doesn't happen by default as you might have expected ;-)

您必须将mouseListener添加到面板中。这不会发生在默认情况下，如你可能预期;

MainClass1() {
    addMouseListener(this);
}

BTW: it's not recommended to expose public api that's only meant to be used internally. So instead of letting the panel implement MouseListener (which enforces the public exposure), let the panel create and use a MouseListener:

顺便说一下，不建议公开只用于内部的公共api。因此，与其让面板实现MouseListener(强制公众曝光)，不如让面板创建并使用MouseListener:

private MouseListener mouseListener;
MainClass1() {
   mouseListener = createMouseListener();
   addMouseListener(mouseListener);
}

protected MouseListener createMouseListener() {
    MouseListener l = new MouseListener() {

    }
   return l;
}

BTW 2: calling the repaint on the limited area isn't exactly what you want (?) - it temporarily adds the squares to the painting, they are lost whenever the whole panel is repainted (same effect as with getGraphics). Depending on what you really want,

顺便说一句:在有限的区域调用重绘并不是你想要的(?)——它临时地将方块添加到绘画中，当整个面板被重绘时它们就会丢失(与getGraphics相同的效果)。取决于你真正想要什么，

• paint a single square at the most recently clicked position: call repaint()
• 在最近单击的位置上绘制一个正方形:调用repaint()
• paint squares at all locations ever clicked: store the locations in a list and implement repaint to loop over that list. Here you may call the repaint with parameters, but why bother?
• 在所有点击过的位置上绘制方块:将位置存储在一个列表中，并实现repaint对该列表进行循环。在这里，您可以调用重新绘制参数，但是为什么要麻烦呢?

#2

This is not an immediate answer to your question, but knowing (or at least suspecting) what it is that you wish to offer (a simple paint program), I suggest starting with this approach based around a BufferedImage as the painting surface..

这不是对你的问题的直接回答，但是知道(或者至少是怀疑)你想要提供的是什么(一个简单的油漆程序)，我建议从基于BufferedImage(油漆表面)的方法开始。

import java.awt.*;
import java.awt.RenderingHints.Key;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import javax.imageio.ImageIO;
import javax.swing.*;
import javax.swing.border.*;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
import javax.swing.filechooser.FileFilter;
import javax.swing.filechooser.FileNameExtensionFilter;

public class BasicPaint {

    /** Reference to the original image. */
    private BufferedImage originalImage;
    /** Image used to make changes. */
    private BufferedImage canvasImage;
    /** The main GUI that might be added to a frame or applet. */
    private JPanel gui;
    /** The color to use when calling clear, text or other 
     * drawing functionality. */
    private Color color = Color.WHITE;
    /** General user messages. */
    private JLabel output = new JLabel("You DooDoodle!");

    private BufferedImage colorSample = new BufferedImage(
            16,16,BufferedImage.TYPE_INT_RGB);
    private JLabel imageLabel;
    private int activeTool;
    public static final int SELECTION_TOOL = 0;
    public static final int DRAW_TOOL = 1;
    public static final int TEXT_TOOL = 2;

    private Point selectionStart; 
    private Rectangle selection;
    private boolean dirty = false;
    private Stroke stroke = new BasicStroke(
            3,BasicStroke.CAP_ROUND,BasicStroke.JOIN_ROUND,1.7f);
    private RenderingHints renderingHints;

    public JComponent getGui() {
        if (gui==null) {
            Map<Key, Object> hintsMap = new HashMap<RenderingHints.Key,Object>();
            hintsMap.put(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
            hintsMap.put(RenderingHints.KEY_DITHERING, RenderingHints.VALUE_DITHER_ENABLE);
            hintsMap.put(RenderingHints.KEY_TEXT_ANTIALIASING, RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
            renderingHints = new RenderingHints(hintsMap); 

            setImage(new BufferedImage(320,240,BufferedImage.TYPE_INT_RGB));
            gui = new JPanel(new BorderLayout(4,4));
            gui.setBorder(new EmptyBorder(5,3,5,3));

            JPanel imageView = new JPanel(new GridBagLayout());
            imageView.setPreferredSize(new Dimension(480,320));
            imageLabel = new JLabel(new ImageIcon(canvasImage));
            JScrollPane imageScroll = new JScrollPane(imageView);
            imageView.add(imageLabel);
            imageLabel.addMouseMotionListener(new ImageMouseMotionListener());
            imageLabel.addMouseListener(new ImageMouseListener());
            gui.add(imageScroll,BorderLayout.CENTER);

            JToolBar tb = new JToolBar();
            tb.setFloatable(false);
            JButton colorButton = new JButton("Color");
            colorButton.setMnemonic('o');
            colorButton.setToolTipText("Choose a Color");
            ActionListener colorListener = new ActionListener() {
                public void actionPerformed(ActionEvent arg0) {
                    Color c = JColorChooser.showDialog(
                            gui, "Choose a color", color);
                    if (c!=null) {
                        setColor(c);
                    }
                }
            };
            colorButton.addActionListener(colorListener);
            colorButton.setIcon(new ImageIcon(colorSample));
            tb.add(colorButton);

            setColor(color);

            final SpinnerNumberModel strokeModel = 
                    new SpinnerNumberModel(3,1,16,1);
            JSpinner strokeSize = new JSpinner(strokeModel);
            ChangeListener strokeListener = new ChangeListener() {
                @Override
                public void stateChanged(ChangeEvent arg0) {
                    Object o = strokeModel.getValue();
                    Integer i = (Integer)o; 
                    stroke = new BasicStroke(
                            i.intValue(),
                            BasicStroke.CAP_ROUND,
                            BasicStroke.JOIN_ROUND,
                            1.7f);
                }
            };
            strokeSize.addChangeListener(strokeListener);
            strokeSize.setMaximumSize(strokeSize.getPreferredSize());
            JLabel strokeLabel = new JLabel("Stroke");
            strokeLabel.setLabelFor(strokeSize);
            strokeLabel.setDisplayedMnemonic('t');
            tb.add(strokeLabel);
            tb.add(strokeSize);

            tb.addSeparator();

            ActionListener clearListener = new ActionListener() {
                public void actionPerformed(ActionEvent arg0) {
                    int result = JOptionPane.OK_OPTION;
                    if (dirty) {
                        result = JOptionPane.showConfirmDialog(
                                gui, "Erase the current painting?");
                    }
                    if (result==JOptionPane.OK_OPTION) {
                        clear(canvasImage);
                    }
                }
            };
            JButton clearButton = new JButton("Clear");
            tb.add(clearButton);
            clearButton.addActionListener(clearListener);

            gui.add(tb, BorderLayout.PAGE_START);

            JToolBar tools = new JToolBar(JToolBar.VERTICAL);
            tools.setFloatable(false);
            JButton crop = new JButton("Crop");
            final JRadioButton select = new JRadioButton("Select", true);
            final JRadioButton draw = new JRadioButton("Draw");
            final JRadioButton text = new JRadioButton("Text");

            tools.add(crop);            
            tools.add(select);          
            tools.add(draw);            
            tools.add(text);

            ButtonGroup bg = new ButtonGroup();
            bg.add(select);
            bg.add(text);
            bg.add(draw);
            ActionListener toolGroupListener = new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent ae) {
                    if (ae.getSource()==select) {
                        activeTool = SELECTION_TOOL;
                    } else if (ae.getSource()==draw) {
                        activeTool = DRAW_TOOL;
                    } else if (ae.getSource()==text) {
                        activeTool = TEXT_TOOL;
                    }
                }
            };
            select.addActionListener(toolGroupListener);
            draw.addActionListener(toolGroupListener);
            text.addActionListener(toolGroupListener);

            gui.add(tools, BorderLayout.LINE_END);

            gui.add(output,BorderLayout.PAGE_END);
            clear(colorSample);
            clear(canvasImage);
        }

        return gui;
    }

    /** Clears the entire image area by painting it with the current color. */
    public void clear(BufferedImage bi) {
        Graphics2D g = bi.createGraphics();
        g.setRenderingHints(renderingHints);
        g.setColor(color);
        g.fillRect(0, 0, bi.getWidth(), bi.getHeight());

        g.dispose();
        imageLabel.repaint();
    }

    public void setImage(BufferedImage image) {
        this.originalImage = image;
        int w = image.getWidth();
        int h = image.getHeight();
        canvasImage = new BufferedImage(w,h,BufferedImage.TYPE_INT_ARGB);

        Graphics2D g = this.canvasImage.createGraphics();
        g.setRenderingHints(renderingHints);
        g.drawImage(image, 0, 0, gui);
        g.dispose();

        selection = new Rectangle(0,0,w,h); 
        if (this.imageLabel!=null) {
            imageLabel.setIcon(new ImageIcon(canvasImage));
            this.imageLabel.repaint();
        }
        if (gui!=null) {
            gui.invalidate();
        }
    }

    /** Set the current painting color and refresh any elements needed. */
    public void setColor(Color color) {
        this.color = color;
        clear(colorSample);
    }

    private JMenu getFileMenu(boolean webstart){
        JMenu file = new JMenu("File");
        file.setMnemonic('f');

        JMenuItem newImageItem = new JMenuItem("New");
        newImageItem.setMnemonic('n');
        ActionListener newImage = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent arg0) {
                BufferedImage bi = new BufferedImage(
                        360, 300, BufferedImage.TYPE_INT_ARGB);
                clear(bi);
                setImage(bi);
            }
        };
        newImageItem.addActionListener(newImage);
        file.add(newImageItem);

        if (webstart) {
            //TODO Add open/save functionality using JNLP API
        } else {
            //TODO Add save functionality using J2SE API
            file.addSeparator();
            ActionListener openListener = new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent arg0) {
                    if (!dirty) {
                        JFileChooser ch = getFileChooser();
                        int result = ch.showOpenDialog(gui);
                        if (result==JFileChooser.APPROVE_OPTION ) {
                            try {
                                BufferedImage bi = ImageIO.read(
                                        ch.getSelectedFile());
                                setImage(bi);
                            } catch (IOException e) {
                                showError(e);
                                e.printStackTrace();
                            }
                        }
                    } else {
                        // TODO
                        JOptionPane.showMessageDialog(
                                gui, "TODO - prompt save image..");
                    }
                }
            };
            JMenuItem openItem = new JMenuItem("Open");
            openItem.setMnemonic('o');
            openItem.addActionListener(openListener);
            file.add(openItem);

            ActionListener saveListener = new ActionListener() {

                @Override
                public void actionPerformed(ActionEvent e) {
                    JFileChooser ch = getFileChooser();
                    int result = ch.showSaveDialog(gui);
                    if (result==JFileChooser.APPROVE_OPTION ) {
                        try {
                            File f = ch.getSelectedFile();
                            ImageIO.write(BasicPaint.this.canvasImage, "png", f);
                            BasicPaint.this.originalImage = BasicPaint.this.canvasImage;
                            dirty = false;
                        } catch (IOException ioe) {
                            showError(ioe);
                            ioe.printStackTrace();
                        }
                    }
                }
            };
            JMenuItem saveItem = new JMenuItem("Save");
            saveItem.addActionListener(saveListener);
            saveItem.setMnemonic('s');
            file.add(saveItem);
        }

        if (canExit()) {
            ActionListener exit = new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent arg0) {
                    // TODO Auto-generated method stub
                    System.exit(0);
                }
            };
            JMenuItem exitItem = new JMenuItem("Exit");
            exitItem.setMnemonic('x');
            file.addSeparator();
            exitItem.addActionListener(exit);
            file.add(exitItem);
        }

        return file;
    }

    private void showError(Throwable t) {
        JOptionPane.showMessageDialog(
                gui, 
                t.getMessage(), 
                t.toString(), 
                JOptionPane.ERROR_MESSAGE);
    }

    JFileChooser chooser = null;

    public JFileChooser getFileChooser() {
        if (chooser==null) {
            chooser = new JFileChooser();
            FileFilter ff = new FileNameExtensionFilter("Image files", ImageIO.getReaderFileSuffixes());
            chooser.setFileFilter(ff);
        }
        return chooser;

    }

    public boolean canExit() {
        boolean canExit = false;
        SecurityManager sm = System.getSecurityManager();
        if (sm==null) {
            canExit = true;
        } else {
            try {
                sm.checkExit(0);
                canExit = true; 
            } catch(Exception stayFalse) {
            }
        }

        return canExit;
    }

    public JMenuBar getMenuBar(boolean webstart){
        JMenuBar mb = new JMenuBar();
        mb.add(this.getFileMenu(webstart));
        return mb;
    }

    public static void main(String[] args) {
        Runnable r = new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(
                            UIManager.getSystemLookAndFeelClassName());
                } catch (Exception e) {
                    // use default
                }
                BasicPaint bp = new BasicPaint();

                JFrame f = new JFrame("DooDoodle!");
                f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
                f.setLocationByPlatform(true);

                f.setContentPane(bp.getGui());
                f.setJMenuBar(bp.getMenuBar(false));

                f.pack();
                f.setMinimumSize(f.getSize());
                f.setVisible(true);
            }
        };
        SwingUtilities.invokeLater(r);
    }

    public void text(Point point) {
        String text = JOptionPane.showInputDialog(gui, "Text to add", "Text");
        if (text!=null) {
            Graphics2D g = this.canvasImage.createGraphics();
            g.setRenderingHints(renderingHints);
            g.setColor(this.color);
            g.setStroke(stroke);
            int n = 0;
            g.drawString(text,point.x,point.y);
            g.dispose();
            this.imageLabel.repaint();
        }
    }

    public void draw(Point point) {
        Graphics2D g = this.canvasImage.createGraphics();
        g.setRenderingHints(renderingHints);
        g.setColor(this.color);
        g.setStroke(stroke);
        int n = 0;
        g.drawLine(point.x, point.y, point.x+n, point.y+n);
        g.dispose();
        this.imageLabel.repaint();
    }

    class ImageMouseListener extends MouseAdapter {

        @Override
        public void mousePressed(MouseEvent arg0) {
            // TODO Auto-generated method stub
            if (activeTool==BasicPaint.SELECTION_TOOL) {
                selectionStart = arg0.getPoint();
            } else if (activeTool==BasicPaint.DRAW_TOOL) {
                // TODO
                draw(arg0.getPoint());
            } else if (activeTool==BasicPaint.TEXT_TOOL) {
                // TODO
                text(arg0.getPoint());
            } else {
                JOptionPane.showMessageDialog(
                        gui, 
                        "Application error.  :(", 
                        "Error!", 
                        JOptionPane.ERROR_MESSAGE);
            }
        }

        @Override
        public void mouseReleased(MouseEvent arg0) {
            if (activeTool==BasicPaint.SELECTION_TOOL) {
                selection = new Rectangle(
                        selectionStart.x,
                        selectionStart.y,
                        arg0.getPoint().x,
                        arg0.getPoint().y);
            }
        }
    }

    class ImageMouseMotionListener implements MouseMotionListener {

        @Override
        public void mouseDragged(MouseEvent arg0) {
            reportPositionAndColor(arg0);
            if (activeTool==BasicPaint.SELECTION_TOOL) {
                selection = new Rectangle(
                        selectionStart.x,
                        selectionStart.y,
                        arg0.getPoint().x-selectionStart.x,
                        arg0.getPoint().y-selectionStart.y);
            } else if (activeTool==BasicPaint.DRAW_TOOL) {
                draw(arg0.getPoint());
            }
        }

        @Override
        public void mouseMoved(MouseEvent arg0) {
            reportPositionAndColor(arg0);
        }

    }

    private void reportPositionAndColor(MouseEvent me) {
        String text = "";
        if (activeTool==BasicPaint.SELECTION_TOOL) {
            text += "Selection (X,Y:WxH): " + 
                    (int)selection.getX() +
                    "," +
                    (int)selection.getY() +
                    ":" +
                    (int)selection.getWidth() +
                    "x" +
                    (int)selection.getHeight();
        } else {
            text += "X,Y: " + (me.getPoint().x+1) + "," + (me.getPoint().y+1);
        }
        output.setText(text);
    }
}

This source is very patchy.

这个来源非常不完整。

• It has many parts with // TODO
• 它有许多部件
• A dirty attribute is declared but never used in any meaningful way. ..
• 一个肮脏的属性被声明，但从未被用在任何有意义的方式。

It is just something I hacked together today and thought should be shown before it hit the posting limit.

这只是我今天一起破解的东西，我认为应该在它达到发帖限制之前显示出来。

Oh, and don't go looking for any 'OO design' since I did not put any in. If there is any, it is only by accident. This code is intended to demonstrate what is possible and how to start doing it.

哦，不要去寻找任何“OO设计”，因为我没有放入任何。如果有的话，那只是偶然。这段代码旨在演示什么是可能的，以及如何开始。

#3

Note the typo in your method:

注意你的方法中的错别字:

public void paintComponent(Graphics g){

    super.paintComponents(g);
    g.setColor(Color.RED);
    g.fillRect(varx, vary, 10, 10);     

}

Your method is named paintComponent while you are calling super.paintComponents (plural). If you override a method (and I would strongly suggest to add an @Override tag to avoid that due to a typo you are actually overriding nothing) like paintComponent, make sure to call the super method (the same method, and not another one).

您的方法在调用super时被命名为paintComponent。paintComponents(复数)。如果您覆盖一个方法(我强烈建议添加一个@Override标记，以避免由于拼写错误而重写任何东西)，比如paintComponent，请确保调用super方法(相同的方法，而不是另一个)。

#4

Firstly, the PaintClass11 is never used...

首先，PaintClass11从未被使用过……

Secondly even if it was, you create two separate instances of the PaintClass22, one that is placed on the frame and one which you are trying to update...so no updates will ever occur on the screen.

其次，即使是这样，您也要创建两个单独的PaintClass22实例，一个放在框架上，另一个正在尝试更新……所以屏幕上不会出现任何更新。

You don't need two separate classes. Merge PaintClass11 and PaintClass22 into a single class and add that to your frame

您不需要两个单独的类。将PaintClass11和PaintClass22合并成一个类并将其添加到框架中。