限制jTextArea文本长度，退格键无法正常工作

时间：2014-07-06 20:17:06

标签： java swing netbeans limit jtextarea

所以我在我的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。

限制的作用是，当用户未单击“提交”按钮时，它将函数 CheckSize（）作为新线程运行。 CheckSize（）查看jTextArea的内容，它具有长度条件。一旦满足溢出长度（256个字符），就会调用 enforceLimit（）将插入符号放在textarea的末尾并退回一个字符。

现在的问题是，在测试期间，它会满足溢出长度条件和随机退格一个，两个甚至三个字符，永远不会直到文本长度为256.换句话说，如果有257字符，应用程序选择是否要退格直到256，或255或254.简单地说，它不听取给出的指示 - 或者我没有说明我的指示......？

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）的限制为256个字符（lblChar）。用户键入最多字符数的那一刻，应用程序显示字数太高，然后假设退格键入的字符，将消息内容缩短为仅256个字符。

我发现了在另一个SO示例中使用机器人的想法。

Screenshot of Desktop App

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                   
}

1 个答案:

答案 0 :(得分：2)

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();
         }
      });
   }
}
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