所以我在桌面应用程序中创建了一个文本限制功能，但我似乎无法让它在正确的位置停止退格。
该限制的作用是，在用户未单击“提交”按钮时将函数 CheckSize() 作为新线程运行。 CheckSize() 查看 jTextArea 的内容，它有长度条件。一旦达到溢出长度(256 个字符)，enforceLimit() 就会被调用，将插入符号放在文本区域的末尾，并退格一个字符。
现在的问题是，在测试过程中，它会满足溢出长度条件并随机退格一个、两个甚至三个字符，而不仅仅是直到文本长度为256。换句话说，如果有257字符，应用程序选择是否要退格到 256、255 或 254。简单地说，它不听给出的说明 - 或者我的说明不够清楚..？
在下面的屏幕截图中，您将看到用户创建了一条消息，并且消息内容 (txtMessage) 的长度限制为 256 个字符 (lblChar)。当用户输入的字符数达到最大字符数时，应用程序会显示字数过高，然后据称会对键入的字符进行退格，以将消息内容缩短为仅 256 个字符。 p>
我在另一个 SO 示例中发现了使用机器人的想法。
代码:
import com.alee.laf.WebLookAndFeel;
import java.awt.AWTException;
import java.awt.Color;
import java.awt.Cursor;
import java.awt.Robot;
import java.awt.event.KeyEvent;
import javax.swing.text.DocumentFilter;
public class AddBulletin extends javax.swing.JFrame {
public AddBulletin() {
WebLookAndFeel.install();
initComponents();
CheckSize();
}
private void CheckSize() {
Thread thread = new Thread() {
public void run() {
do {
int txtLen = txtMessage.getText().length();
lblChar.setText(Integer.toString(txtLen));
if (txtLen > (256 - (256 * 0.1)) && txtLen <= 256) {
lblChar.setForeground(Color.orange);
} else if (txtLen > 256) {
lblChar.setForeground(Color.red);
enforceLimit();
} else {
lblChar.setForeground(Color.green);
}
} while (!btnSubmit.isSelected());
}
};
thread.start();
}
private void enforceLimit() {
try {
txtMessage.setCaretPosition(txtMessage.getText().length());
System.out.println("Position: " + txtMessage.getCaretPosition());
Robot r = new Robot();
int bsp = KeyEvent.VK_BACK_SPACE;
r.keyPress(bsp);
r.keyRelease(bsp);
} catch (AWTException ex) {
ex.printStackTrace(System.err);
}
}
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {
jPanel1 = new javax.swing.JPanel();
txtTitle = new javax.swing.JTextField();
jLabel2 = new javax.swing.JLabel();
jLabel3 = new javax.swing.JLabel();
jScrollPane1 = new javax.swing.JScrollPane();
txtMessage = new javax.swing.JTextArea();
jLabel4 = new javax.swing.JLabel();
lblChar = new javax.swing.JLabel();
jLabel6 = new javax.swing.JLabel();
jTextField2 = new javax.swing.JTextField();
btnClear = new javax.swing.JButton();
btnSubmit = new javax.swing.JButton();
btnCancel = new javax.swing.JButton();
jLabel7 = new javax.swing.JLabel();
cboType = new javax.swing.JComboBox();
jPanel2 = new javax.swing.JPanel();
jLabel1 = new javax.swing.JLabel();
jPanel3 = new javax.swing.JPanel();
jSeparator1 = new javax.swing.JSeparator();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
setBackground(new java.awt.Color(102, 102, 255));
jPanel1.setBackground(new java.awt.Color(102, 102, 255));
jLabel2.setForeground(new java.awt.Color(255, 255, 255));
jLabel2.setText("Title:");
jLabel3.setForeground(new java.awt.Color(255, 255, 255));
jLabel3.setText("Message:");
txtMessage.setColumns(20);
txtMessage.setFont(new java.awt.Font("Tahoma", 0, 11)); // NOI18N
txtMessage.setLineWrap(true);
txtMessage.setRows(5);
txtMessage.addKeyListener(new java.awt.event.KeyAdapter() {
public void keyReleased(java.awt.event.KeyEvent evt) {
txtMessageKeyReleased(evt);
}
});
jScrollPane1.setViewportView(txtMessage);
jLabel4.setFont(new java.awt.Font("Tahoma", 1, 11)); // NOI18N
jLabel4.setForeground(new java.awt.Color(255, 255, 255));
jLabel4.setText("/ 256");
lblChar.setFont(new java.awt.Font("Tahoma", 1, 11)); // NOI18N
lblChar.setHorizontalAlignment(javax.swing.SwingConstants.RIGHT);
lblChar.setText("0");
jLabel6.setForeground(new java.awt.Color(255, 255, 255));
jLabel6.setText("Author:");
jTextField2.setEditable(false);
btnClear.setText("Clear");
btnClear.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
btnClearActionPerformed(evt);
}
});
btnSubmit.setText("Submit");
btnCancel.setText("Cancel");
btnCancel.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
btnCancelActionPerformed(evt);
}
});
jLabel7.setForeground(new java.awt.Color(255, 255, 255));
jLabel7.setText("Type:");
cboType.setModel(new javax.swing.DefaultComboBoxModel(new String[] { "Information", "Announcement" }));
javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
jPanel1.setLayout(jPanel1Layout);
jPanel1Layout.setHorizontalGroup(
jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel1Layout.createSequentialGroup()
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addGap(23, 23, 23)
.addComponent(jLabel2, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED))
.addGroup(jPanel1Layout.createSequentialGroup()
.addGap(23, 23, 23)
.addComponent(jLabel3, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addGap(8, 8, 8)))
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 297, Short.MAX_VALUE)
.addComponent(txtTitle)))
.addGroup(javax.swing.GroupLayout.Alignment.LEADING, jPanel1Layout.createSequentialGroup()
.addGap(23, 23, 23)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel1Layout.createSequentialGroup()
.addGap(0, 0, Short.MAX_VALUE)
.addComponent(btnClear, javax.swing.GroupLayout.PREFERRED_SIZE, 74, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(52, 52, 52)
.addComponent(btnSubmit, javax.swing.GroupLayout.PREFERRED_SIZE, 101, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(52, 52, 52)
.addComponent(btnCancel, javax.swing.GroupLayout.PREFERRED_SIZE, 73, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel1Layout.createSequentialGroup()
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING)
.addComponent(jLabel7, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(jLabel6, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addGap(246, 246, 246)
.addComponent(lblChar, javax.swing.GroupLayout.PREFERRED_SIZE, 28, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(jLabel4))
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel1Layout.createSequentialGroup()
.addGap(8, 8, 8)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addComponent(cboType, javax.swing.GroupLayout.Alignment.TRAILING, 0, 297, Short.MAX_VALUE)
.addComponent(jTextField2, javax.swing.GroupLayout.Alignment.TRAILING))))))))
.addGap(23, 23, 23))
);
jPanel1Layout.setVerticalGroup(
jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addContainerGap()
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(txtTitle, javax.swing.GroupLayout.DEFAULT_SIZE, 21, Short.MAX_VALUE)
.addComponent(jLabel2))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jLabel3)
.addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 96, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jLabel4)
.addComponent(lblChar)))
.addGroup(jPanel1Layout.createSequentialGroup()
.addGap(25, 25, 25)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jLabel6)
.addComponent(jTextField2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))))
.addGap(6, 6, 6)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jLabel7)
.addComponent(cboType, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(btnClear)
.addComponent(btnCancel))
.addComponent(btnSubmit))
.addContainerGap())
);
jPanel2.setBackground(new java.awt.Color(102, 102, 255));
jLabel1.setBackground(new java.awt.Color(102, 102, 255));
jLabel1.setFont(new java.awt.Font("Tahoma", 1, 36)); // NOI18N
jLabel1.setForeground(new java.awt.Color(255, 255, 255));
jLabel1.setHorizontalAlignment(javax.swing.SwingConstants.CENTER);
jLabel1.setText("Create Message");
javax.swing.GroupLayout jPanel2Layout = new javax.swing.GroupLayout(jPanel2);
jPanel2.setLayout(jPanel2Layout);
jPanel2Layout.setHorizontalGroup(
jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jLabel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
);
jPanel2Layout.setVerticalGroup(
jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jLabel1)
);
jPanel3.setBackground(new java.awt.Color(102, 102, 255));
javax.swing.GroupLayout jPanel3Layout = new javax.swing.GroupLayout(jPanel3);
jPanel3.setLayout(jPanel3Layout);
jPanel3Layout.setHorizontalGroup(
jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel3Layout.createSequentialGroup()
.addComponent(jSeparator1)
.addGap(0, 0, 0))
);
jPanel3Layout.setVerticalGroup(
jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jSeparator1, javax.swing.GroupLayout.PREFERRED_SIZE, 2, javax.swing.GroupLayout.PREFERRED_SIZE)
);
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jPanel2, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
.addComponent(jPanel3, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
.addGap(0, 0, Short.MAX_VALUE))
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addComponent(jPanel2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(0, 0, 0)
.addComponent(jPanel3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(0, 0, 0)
.addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
);
pack();
}// </editor-fold>
private void btnCancelActionPerformed(java.awt.event.ActionEvent evt) {
this.dispose();
}
private void btnClearActionPerformed(java.awt.event.ActionEvent evt) {
txtMessage.setText("");
txtTitle.setText("");
}
/**
* @param args the command line arguments
*/
public static void main(String args[]) {
try {
for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
if ("Nimbus".equals(info.getName())) {
javax.swing.UIManager.setLookAndFeel(info.getClassName());
break;
}
}
} catch (ClassNotFoundException ex) {
java.util.logging.Logger.getLogger(AddBulletin.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
java.util.logging.Logger.getLogger(AddBulletin.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
java.util.logging.Logger.getLogger(AddBulletin.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (javax.swing.UnsupportedLookAndFeelException ex) {
java.util.logging.Logger.getLogger(AddBulletin.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
}
//</editor-fold>
/* Create and display the form */
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new AddBulletin().setVisible(true);
}
});
}
// Variables declaration - do not modify
private javax.swing.JButton btnCancel;
private javax.swing.JButton btnClear;
private javax.swing.JButton btnSubmit;
private javax.swing.JComboBox cboType;
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel2;
private javax.swing.JLabel jLabel3;
private javax.swing.JLabel jLabel4;
private javax.swing.JLabel jLabel6;
private javax.swing.JLabel jLabel7;
private javax.swing.JPanel jPanel1;
private javax.swing.JPanel jPanel2;
private javax.swing.JPanel jPanel3;
private javax.swing.JScrollPane jScrollPane1;
private javax.swing.JSeparator jSeparator1;
private javax.swing.JTextField jTextField2;
private javax.swing.JLabel lblChar;
private javax.swing.JTextArea txtMessage;
private javax.swing.JTextField txtTitle;
// End of variables declaration
}
最佳答案
我的最小可运行示例。再次使用 DocumentFilter:
import javax.swing.*;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.DocumentFilter;
import javax.swing.text.PlainDocument;
@SuppressWarnings("serial")
public class EnforceSizeTest extends JPanel {
private static final int MAX_LENGTH = 256;
private JTextArea textArea = new JTextArea(15, 20);
public EnforceSizeTest() {
textArea.setWrapStyleWord(true);
textArea.setLineWrap(true);
((PlainDocument) textArea.getDocument()).setDocumentFilter(new MyDocumentFilter(MAX_LENGTH));
add(new JScrollPane(textArea));
}
private class MyDocumentFilter extends DocumentFilter {
private static final int MAX_LENGTH = 256;
private int maxLength;
public MyDocumentFilter(int maxLength) {
this.maxLength = maxLength;
}
@Override
public void insertString(FilterBypass fb, int offset, String string,
AttributeSet attr) throws BadLocationException {
Document doc = fb.getDocument();
StringBuilder sb = new StringBuilder();
sb.append(doc.getText(0, doc.getLength()));
sb.insert(offset, string);
if (sb.length() > maxLength) {
return;
}
super.insertString(fb, offset, string, attr);
}
@Override
public void replace(FilterBypass fb, int offset, int length, String text,
AttributeSet attrs) throws BadLocationException {
Document doc = fb.getDocument();
StringBuilder sb = new StringBuilder();
sb.append(doc.getText(0, doc.getLength()));
sb.replace(offset, offset + length, text);
if (sb.length() > MAX_LENGTH) {
return;
}
super.replace(fb, offset, length, text, attrs);
}
}
private static void createAndShowGui() {
EnforceSizeTest mainPanel = new EnforceSizeTest();
JFrame frame = new JFrame("EnforceSizeTest");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
关于java - 使用退格键限制 jTextArea 文本长度无法正常工作，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/24599936/