java - 每次变量更改时更新 JTextFields 文本

Question

你好，我是 Java 的新手，我正在尝试编写一个非常简单的练习来练习，我创建了一个 Jclass 来从数据库读取参数并将其保存在名为“estado”的变量和一个 JFrame 中显示该变量的值在数据库中随机变化。

该程序读取 MySql DB 并将所需的数据存储在 Java 变量中，如下所示:

package Paquete_domotica;

import java.io.*;
import java.sql.*;    

public class domotica {

  public static int estado;
  boolean loop = true;

    public domotica() throws IOException 
    {
        while(loop)
        {
        try
        {                
            DriverManager.registerDriver(new org.gjt.mm.mysql.Driver());
            Connection conexion = DriverManager.getConnection (
                "jdbc:mysql://localhost/XXX","XXXX", "XXXX");                
            Statement s = conexion.createStatement(); 
            ResultSet rs = s.executeQuery ("select id, nombre, valor from data");                
            while (rs.next())
            {
               if (rs.getInt ("id") == 20)
               {                   
               estado = rs.getInt ("valor");                   
               }              
            }
            rs.close();
            conexion.close();
        }
        catch (SQLException e)
        {
            e.printStackTrace();
        }

       }
    }
}

存储的变量称为“estado”，这些变量是 1 或 0，我尝试这些变量的每次更改都会更改以下 Jframe 中 jTextField1 的值:

package Paquete_domotica;

import java.awt.event.ActionListener;
import java.io.IOException;

public class JFramedomotica extends javax.swing.JFrame {

    int numeroRecibido;

    public JFramedomotica() {
        initComponents();
    }
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        jTextField1 = new javax.swing.JTextField();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jTextField1.setHorizontalAlignment(javax.swing.JTextField.CENTER);
        jTextField1.setText("SIN DATOS");
        jTextField1.setCursor(new java.awt.Cursor(java.awt.Cursor.TEXT_CURSOR));
        jTextField1.setEnabled(false);
        jTextField1.addMouseListener(new java.awt.event.MouseAdapter() {
            public void mouseClicked(java.awt.event.MouseEvent evt) {
                jTextField1MouseClicked(evt);
            }
        });

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(110, 110, 110)
                .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, 136, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(154, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(138, 138, 138)
                .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(142, Short.MAX_VALUE))
        );

            pack();
        }// </editor-fold>                        

private void jTextField1MouseClicked(java.awt.event.MouseEvent evt) {                                         
      jTextField1.setText(String.valueOf(domotica.estado)); 
    }

        public static void main(String args[]) throws IOException {
            /* Set the Nimbus look and feel */
            //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        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(JFramedomotica.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(JFramedomotica.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(JFramedomotica.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(JFramedomotica.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 JFramedomotica().setVisible(true);
            }
        });
        new domotica();

    }

    // Variables declaration - do not modify                     
    private javax.swing.JTextField jTextField1;
    // End of variables declaration                   


  }

正如您现在所看到的，我可以使用

更新 jTextField1

private void jTextField1MouseClicked(java.awt.event.MouseEvent evt) {                                         
      jTextField1.setText(String.valueOf(domotica.estado)); 
    }

但是使用这段代码我必须单击鼠标来刷新 jTextField1，我不知道如何在每次更改“estado”时更新 jTextField1。

Answer 1

您的代码有很多错误，如此之多以至于更容易，因此给您一个清晰的示例来说明如何完成此操作。

解决这个问题的关键是将轮询和UI分离，然后引入事件机制来通知UI轮询器检测到的变化。

您的第一个概念是正确的，但是您确实不希望调用线程永远循环，就像您的 domotica 类的情况一样。您希望该类对您隐藏轮询并在数据更改时触发事件，如下所示:

public class Poller
{
  private boolean running;
  private DataSource dataSource;
  private String sql;
  private long pollInterval;
  private List<DataChangeListener> dataChangeListeners;

  public Poller(DataSource dataSource, String sql, long pollInterval)
  {
    this.dataSource = dataSource;
    this.sql = sql;
    this.pollInterval = pollInterval;
    this.running = false;
    this.dataChangeListeners = new CopyOnWriteArrayList<DataChangeListener>();
  }

  public void addDataChangeListener(DataChangeListener dataChangeListener)
  {
    this.dataChangeListeners.add(dataChangeListener);
  }

  public void removeDataChangeListener(DataChangeListener dataChangeListener)
  {
    this.dataChangeListeners.remove(dataChangeListener);
  }

  public boolean isRunning()
  {
    return running;
  }

  public synchronized void start()
  {
    if (!isRunning())
    {
      this.running = true;
      new PollingThread().start();
    }
  }

  public synchronized void stop()
  {
    this.running = false;
  }

  private void fireListeners(Object previousValue, Object newValue)
  {
    for (DataChangeListener dataChangeListener : dataChangeListeners)
    {
      dataChangeListener.dataChanged(previousValue, newValue);
    }     
  }

  private class PollingThread extends Thread
  {
    @Override
    public void run()
    {
      Connection connection = null;
      PreparedStatement statement = null;

      try
      {
        connection = dataSource.getConnection();
        statement = connection.prepareStatement(sql);

        Object previousValue = null;

        while (isRunning())
        {
          ResultSet resultSet = statement.executeQuery();

          while (resultSet.next())
          {
            Object newValue = resultSet.getObject(1); 

            if (!newValue.equals(previousValue))
            {
              fireListeners(previousValue, newValue);
              previousValue = newValue;
            }
          }

          Thread.sleep(pollInterval);
        }
      }
      finally
      {
        if (statement != null) statement.close();
        if (connection != null) connection.close();
      }
    }
  }
}

注意PollerThread 以及它如何处理 JDBC 资源。首先它有一个 sleep 以避免占用CPU。其次，像您的示例中那样重复打开和关闭连接可能会让您的 DBA 感到不安。最好使用 javax.sql.DataSource 并获取循环外部的资源。

然后可以实例化 Poller 类并将其传递到应用程序主框架，如下所示，使用窗口关闭来停止轮询:

SwingUtilities.invokeLater(
  new Runnable() 
  {
    public void run() 
    {
      DataSource dataSource = ...
      String sql = ...         

      final Poller poller = new Poller(dataSource, sql, 1000);

      MainFrame mainFrame = new MainFrame(poller);
      mainFrame.addWindowListener(
        new WindowAdapter() 
        {
          public void windowClosed(WindowEvent event)
          {
            poller.stop():
          }
        }
      );
    }
  }
);

差不多就这样了。

最后一部分是让 MainFrame 监听来自 Poller 的事件并更新 UI。这里重要的是更新应该在 Event Dispatch Thread 上执行。像这样:

public class MainFrame extends JFrame
{
  private JTextField textField;      

  public MainFrame(Poller poller)
  {
    //Create controls first.

    poller.add(new TestFieldUpdateListener());  
    poller.start();
  }

  private class TestFieldUpdateListener implements DataChangeListener 
  {
    public void dataChanged(final Object previousValue, final Object newValue)
    {
      SwingUtilities.invokeLater(
        new Runnable()
        {
          public void run()
          { 
            textField.setText(newValue.toString());
          }
        }
      );
    }
  }
}

就是这样。这个示例应该为您提供要点，它缺少必要的异常处理、null 检查等，但这应该很容易添加。