将MouseListener添加到面板

我正在尝试将鼠标操作添加到我的面板。 这是程序应该做的：

编写一个程序，允许用户通过三次鼠标按下指定三角形。 第一次鼠标按下后，画一个小点。 在第二次鼠标按下后，绘制一条连接前两点的线。 第三次鼠标按下后，绘制整个三角形。 第四次鼠标按下删除旧三角形并开始一个新三角形。

Answer 1

我没有看到你实例化类MouseListen的任何地方。 您还需要调用addMouseListener（）。

以下是我写的一段时间后的作品：

 public class ColorPanel extends JPanel implements MouseListener { . . . ColorPanel(JTextField jTextFieldColor) { super(); this.jTextField = jTextFieldColor; addMouseListener(this); } @Override public void mouseClicked(MouseEvent evt) { System.out.println("Instance of ColorPanel clicked."); jColorChooser = new JColorChooser(this.getBackground()); this.add(jColorChooser); int retval = JOptionPane.showConfirmDialog(null, jColorChooser, "JOptionPane Example : ", JOptionPane.OK_CANCEL_OPTION, JOptionPane.PLAIN_MESSAGE); if (retval == JOptionPane.OK_OPTION) { jTextField.setText(Utils.hexStringFromColor(jColorChooser.getColor())); } } 

请参阅https://docs.oracle.com/javase/tutorial/uiswing/events/mouselistener.html上的教程。

此外，基于https://docs.oracle.com/javase/tutorial/uiswing/events/eventsandcomponents.html ，您可能可以让您的JFrame实现MouseListener，这将使您的代码更简单。 （你根本不需要类MouseListen。）

我写过的快速grep虽然过去的Java代码证实了你可以

 public class MyFrame extends JFrame implements MouseListener 

所以你可能想看看这个。

Answer 2

我强烈建议您先阅读如何编写鼠标侦听器 。 当你遇到困难时，这些教程（以及JavaDocs）是最好的入门之地

你问题的“直接”答案是，你需要在你的组件中注册一个MouseListener实例，可能就像…

 private JPanel createCenterPanel() { panel.addMouseListener(new MouseListen()); //panel.setLayout(null); return panel; } 

这将“回答”您的直接问题。

但是，您会发现很难尝试将MouseListener的操作与面板结合起来，该面板需要绘制结果。

一个更好的解决方案可能是从一个管理它自己的MouseListener的JPanel开始

此外， Graphics g = panel.getGraphics()不是应该如何执行自定义绘画。 请查看执行自定义绘画以获取更多详细信息

所以，相反，它可能看起来更像……

 public class TrianglePanel extends JPanel { private List points = new ArrayList<>(3); public TrianglePanel() { addMouseListener(new MouseListen()); } @Override public Dimension getPreferredSize() { return new Dimension(200, 200); } @Override protected void paintComponent(Graphics g) { super.paintComponent(g); //To change body of generated methods, choose Tools | Templates. if (points.size() < 1) { return; } for (int index = 0; index < points.size(); index++) { Point nextPoint = points.get(index); g.fillOval(nextPoint.x - 2, nextPoint.y - 2, 4, 4); } Point startPoint = points.get(0); Point lastPoint = startPoint; for (int index = 1; index < points.size(); index++) { Point nextPoint = points.get(index); g.drawLine(lastPoint.x, lastPoint.y, nextPoint.x, nextPoint.y); lastPoint = nextPoint; } g.drawLine(lastPoint.x, lastPoint.y, startPoint.x, startPoint.y); } class MouseListen extends MouseAdapter { public void mouseReleased(MouseEvent e) { if (points.size() < 3) { points.add(e.getPoint()); repaint(); } } } } 

Answer 3

我对Swing并不是很熟悉。 作为一名新程序员，我只使用过JavaFX。

但是，您在程序中的任何位置都没有引用MouseListener。 你可能忘了实例化它。

Answer 4

您必须使用addMouseListener方法向Jpanel注册侦听器对象。 更多信息;

• https://docs.oracle.com/javase/7/docs/api/java/awt/event/MouseListener.html

• https://docs.oracle.com/javase/tutorial/uiswing/events/mouselistener.html

Answer 5

cam，鉴于你正在做什么，我跳上了我的“工作机器”并抓住了这段代码。 它在图像顶部绘制一个矩形，只有在您释放鼠标后才显示矩形（这是一项正在进行的工作，未付费，在我的业余时间为我的雇主所喜欢的东西完成）。 但是既然你正在outlook绘图等等，这就是它。

使用JDialog是因为我希望它是模态的; 不要让那困扰你。

 import java.awt.Dimension; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.event.MouseEvent; import java.awt.event.MouseListener; import java.awt.event.WindowEvent; import java.awt.event.WindowListener; import javax.swing.GroupLayout; import javax.swing.JDialog; import javax.swing.JMenu; import javax.swing.JMenuBar; import javax.swing.JMenuItem; import javax.swing.WindowConstants; public class RectSelectGUI extends JDialog implements MouseListener, ActionListener, WindowListener { private static final long serialVersionUID = 1L; public int overheadWd; public int overheadHt; public ImageJPanel imagePanel; private JMenu jMenuSelection; private JMenuBar jMenuBar1; private Dimension mouseDownLoc; private String errorString; public RectSelectGUI(String imgFileName) { initComponents(imgFileName); } private void initComponents(String imgFileName) { imagePanel = new ImageJPanel(imgFileName); jMenuBar1 = new JMenuBar(); jMenuSelection = new JMenu(); JMenuItem jMenuItemSave = new JMenuItem(); jMenuItemSave.setActionCommand("Save"); jMenuItemSave.addActionListener(this); jMenuItemSave.setText("Save"); jMenuSelection.add(jMenuItemSave); JMenuItem jMenuItemCancel = new JMenuItem(); jMenuItemCancel.setActionCommand("Cancel"); jMenuItemCancel.addActionListener(this); jMenuItemCancel.setText("Cancel"); jMenuSelection.add(jMenuItemCancel); mouseDownLoc = new Dimension(); errorString = "No selection"; imagePanel.addMouseListener(this); this.setModal(true); this.setDefaultCloseOperation(WindowConstants.DO_NOTHING_ON_CLOSE); this.addWindowListener(this); GroupLayout jPanel1Layout = new GroupLayout(imagePanel); imagePanel.setLayout(jPanel1Layout); jPanel1Layout.setHorizontalGroup( jPanel1Layout.createParallelGroup(GroupLayout.Alignment.LEADING).addGap(0, 524, Short.MAX_VALUE)); jPanel1Layout.setVerticalGroup( jPanel1Layout.createParallelGroup(GroupLayout.Alignment.LEADING).addGap(0, 370, Short.MAX_VALUE)); jMenuSelection.setText("Selection"); jMenuBar1.add(jMenuSelection); setJMenuBar(jMenuBar1); GroupLayout layout = new GroupLayout(getContentPane()); getContentPane().setLayout(layout); layout.setHorizontalGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup().addContainerGap() .addComponent(imagePanel, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) .addContainerGap())); layout.setVerticalGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup().addContainerGap() .addComponent(imagePanel, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) .addContainerGap())); pack(); overheadWd = this.getWidth() - imagePanel.getWidth(); overheadHt = this.getHeight() - imagePanel.getHeight(); } public String getSelectionString() { if (errorString.isEmpty()) { double rectWd = (double) imagePanel.rectWd; double rectHt = (double) imagePanel.rectHt; double rectX = (double) imagePanel.rectX; double rectY = (double) imagePanel.rectY; if (Math.abs(RectSelect.displayFactor - 1.0) > 0.001) { System.out.println("Adjusting by displayFactor (" + RectSelect.displayFactor + ")"); rectWd /= RectSelect.displayFactor; rectHt /= RectSelect.displayFactor; rectX /= RectSelect.displayFactor; rectY /= RectSelect.displayFactor; } return Math.round(rectWd) + "x" + Math.round(rectHt) + "+" + Math.round(rectX) + "+" + Math.round(rectY); } else { return "ERROR: " + errorString; } } @Override public void mouseClicked(MouseEvent e) { // TODO Auto-generated method stub } @Override public void mousePressed(MouseEvent evt) { mouseDownLoc.setSize(evt.getX(), evt.getY()); } @Override public void mouseReleased(MouseEvent evt) { Dimension mouseUpLoc = new Dimension(evt.getX(), evt.getY()); if (mouseDownLoc.width < mouseUpLoc.width) { imagePanel.rectX = mouseDownLoc.width; imagePanel.rectWd = mouseUpLoc.width - mouseDownLoc.width; } else { imagePanel.rectX = mouseUpLoc.width; imagePanel.rectWd = mouseDownLoc.width - mouseUpLoc.width; } if (mouseDownLoc.height < mouseUpLoc.height) { imagePanel.rectY = mouseDownLoc.height; imagePanel.rectHt = mouseUpLoc.height - mouseDownLoc.height; } else { imagePanel.rectY = mouseUpLoc.height; imagePanel.rectHt = mouseDownLoc.height - mouseUpLoc.height; } imagePanel.haveNewRect = true; imagePanel.repaint(); errorString = ""; } @Override public void actionPerformed(ActionEvent evt) { String cmd = evt.getActionCommand(); switch (cmd) { case "Save": break; case "Cancel": errorString = "Cancelled"; break; default: System.out.println("Unknown action command " + cmd); } this.setVisible(false); } @Override public void windowClosing(WindowEvent e) { errorString = "Cancelled"; this.setVisible(false); } @Override public void mouseEntered(MouseEvent e) { // TODO Auto-generated method stub } @Override public void mouseExited(MouseEvent e) { // TODO Auto-generated method stub } @Override public void windowOpened(WindowEvent e) { try { Thread.sleep(100); } catch (InterruptedException e1) { } this.repaint(); } @Override public void windowClosed(WindowEvent e) { // TODO Auto-generated method stub } @Override public void windowIconified(WindowEvent e) { // TODO Auto-generated method stub } @Override public void windowDeiconified(WindowEvent e) { // TODO Auto-generated method stub } @Override public void windowActivated(WindowEvent e) { } @Override public void windowDeactivated(WindowEvent e) { // TODO Auto-generated method stub } } import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.Image; import java.awt.Toolkit; import javax.swing.JPanel; public class ImageJPanel extends JPanel { private static final long serialVersionUID = 1L; public Image localImage; private int origWd; private int origHt; private int displayWd; private int displayHt; public int rectX; public int rectY; public int rectWd; public int rectHt; public boolean haveNewRect; private Toolkit toolkit; ImageJPanel(String imageFileName) { toolkit = Toolkit.getDefaultToolkit(); localImage = toolkit.getImage(imageFileName); } protected void paintComponent(Graphics g1D) { Graphics2D g; g = (Graphics2D) g1D; // Draw the image using the Graphics object provided g.drawImage(localImage, 0, 0, getDisplayWd(), getDisplayHt(), null); /* * Optional label. Font font = new Font("SansSerif", Font.BOLD, 24); g1D.setFont(font); FontMetrics metrics = g1D.getFontMetrics(); int ht = metrics.getHeight(); int wd = metrics.stringWidth(this.imageFileName); g.setColor(Color.LIGHT_GRAY); g.fillRect(this.getWidth() - wd - 10, this.getHeight() - ht, wd + 10, ht); g1D.setColor(new Color(55, 11, 160)); g1D.drawString(this.imageFileName, this.getWidth() - wd - 10, this.getHeight() - ht + 20); */ // Draw a selection rectangle if requested. if (haveNewRect) { g.drawRect(rectX, rectY, rectWd, rectHt); haveNewRect = false; } } public int getDisplayWd() { return displayWd; } public void setDisplayWd(int displayWd) { this.displayWd = displayWd; } public int getDisplayHt() { return displayHt; } public void setDisplayHt(int displayHt) { this.displayHt = displayHt; } public int getOrigWd() { return origWd; } public void setOrigWd(int origWd) { this.origWd = origWd; } public int getOrigHt() { return origHt; } public void setOrigHt(int origHt) { this.origHt = origHt; } }