的JTable调整列宽不工作的第一次运行

Question

我有一个方法如下：

public void displayTable() throws SQLException{ 

    table = new JTable(){ 
     private static final long serialVersionUID = 1L; 

     @Override 
      public boolean isCellEditable(int row, int column) { 
       return false; 
      } 

    }; 

    stable = new JScrollPane (table); 
    stable.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED); 
    stable.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED); 
    table.setAutoResizeMode(JTable.AUTO_RESIZE_OFF); 
    panel1.add(stable); 
    showTables(); 
} 

而且showTables（），它是这样的：

public void showTables() throws SQLException{ 
    ResultSet showTablesResult = null; 
    query = "abc"; 
    try { 
     showTablesResult = stat.executeQuery("SHOW TABLES"); 
    } catch (SQLException e) { 
     JOptionPane.showMessageDialog(null, "Error connecting to databse"); 
    } 
    DefaultTableModel model = buildTableModel(showTablesResult); 
    updateTable(model);  
} 

updateTable（）：

public void updateTable(DefaultTableModel model){ 
    table.setModel(model); 
    tweakColumns(table); 
} 

现在的问题是，当displayTable初始化运行时，它会生成表格，但列很小，并且不会像应该那样伸出。

当我按下一个运行showTables（）的按钮时，列伸出。我不明白为什么这不起作用，因为displayTable（）运行showTables（）来生成它不是吗？

也可对照这里是tweakColumns（）：

public static void tweakColumns(JTable table){ 
    Enumeration<TableColumn> columns = table.getColumnModel().getColumns(); 

    int required = 0; 
    while(columns.hasMoreElements()){ 
     TableColumn column = columns.nextElement(); 
     int width = (int)table.getTableHeader().getDefaultRenderer() 
        .getTableCellRendererComponent(table, column.getIdentifier() 
          , false, false, -1, column.getModelIndex()).getPreferredSize().getWidth(); 
     required += width; 
    } 

    JViewport viewport = (JViewport)SwingUtilities.getAncestorOfClass(JViewport.class, table); 
    int viewportWidth = viewport.getWidth(); 
    table.setAutoResizeMode(required<viewportWidth ? JTable.AUTO_RESIZE_ALL_COLUMNS : JTable.AUTO_RESIZE_OFF); 
} 

这里是一个MCVE：

import java.awt.BorderLayout; 
import java.awt.Component; 
import java.awt.Dimension; 
import java.awt.EventQueue; 
import java.awt.Image; 
import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 
import java.io.IOException; 
import java.net.URL; 
import java.sql.SQLException; 
import java.util.Enumeration; 
import javax.imageio.ImageIO; 
import javax.swing.BoxLayout; 
import javax.swing.ImageIcon; 
import javax.swing.JButton; 
import javax.swing.JFrame; 
import javax.swing.JLabel; 
import javax.swing.JPanel; 
import javax.swing.JScrollPane; 
import javax.swing.JTabbedPane; 
import javax.swing.JTable; 
import javax.swing.JViewport; 
import javax.swing.SwingUtilities; 
import javax.swing.border.EmptyBorder; 
import javax.swing.table.DefaultTableModel; 
import javax.swing.table.TableColumn; 


public class Main extends JFrame{ 

    private static final long serialVersionUID = 1L; 
    private JPanel panel; 
    private JLabel query = new JLabel("Showing All Tables"); 
    private JTable table; 
    private JPanel panel1; 
    private JScrollPane stable; 
    private Component introLabel; 
    private JPanel contentPane; 
    private JTabbedPane tabbedPane; 
    private JPanel server; 

    public static void main(String[] args) throws InterruptedException { 

      EventQueue.invokeLater(new Runnable() { 
       public void run() { 
        try { 
         Main frame = new Main(); 
         frame.setVisible(true); 
        } catch (Exception e) { 
         e.printStackTrace(); 
        } 
       } 
      }); 
    } 


    public Main() throws IOException, SQLException { 

     setDefaultCloseOperation(javax.swing.JFrame.EXIT_ON_CLOSE); 
     setBounds(100, 100, 655, 470); 
     contentPane = new JPanel(); 
     contentPane.setBorder(new EmptyBorder(5, 5, 5, 5)); 
     contentPane.setLayout(new BorderLayout(1, 1)); 
     setContentPane(contentPane); 

     tabbedPane = new JTabbedPane(JTabbedPane.TOP); 
     contentPane.add(tabbedPane, BorderLayout.CENTER); 

     setResizable(false); 

     server = new JPanel(); 
     server.setLayout(new BorderLayout(0, 0)); 

     DbViewer(); 
    } 

     /** 
     * initial panel setup 
     * @return 
     * @throws SQLException 
     */ 
     public void DbViewer() throws SQLException{ 
      panel = new JPanel(new BorderLayout()); 
      introLabel = makeTextPanel("<html><center>You can use this to browse through the tables used in DEDServer. <br />Double click a Table Name to view it. You can copy a cells value by right clicking on it.<br />Press the home button at the bottom to go back and view all the tables.<br /><br />"+query.getText()+"</center></html>"); 
      panel.add(introLabel,BorderLayout.NORTH); 
      tabbedPane.addTab("DB Viewer",panel); 
      panel1 = new JPanel(); 
      panel1.setLayout(new BoxLayout(panel1, BoxLayout.PAGE_AXIS)); 
      panel.add(panel1,BorderLayout.CENTER); 
      homeButton(); 
      displayTable(); 
     } 


     /** 
     * makes the home button 
     */ 
     public void homeButton(){ 
      JButton button = new JButton(){ 
       private static final long serialVersionUID = 1L; 
        public Dimension getPreferredSize() { 
         return new Dimension(32,32); 
        }; 
       }; 
        try { 
         URL url = new URL("http://png-2.findicons.com/files/icons/1264/clearblack/32/home.png"); 
        Image img = ImageIO.read(url); 
        button.setIcon(new ImageIcon(img)); 
        } catch (IOException ex) { 
        } 
       button.setAlignmentX(Component.CENTER_ALIGNMENT); 
       panel1.add(button); 
       button.addActionListener(new ActionListener() { 
        public void actionPerformed(ActionEvent arg0) { 
         showTables(); 
        } 
      }); 
     } 

     public void updateTable(DefaultTableModel model, JLabel query){ 
      table.setModel(model); 
      tweakColumns(table); 
      introLabel = makeTextPanel("<html><center>You can use this to browse through the tables used in DEDServer. <br />Double click a Table Name to view it. You can copy a cells value by right clicking on it.<br />Press the home button at the bottom to go back and view all the tables.<br /><font color='red'>"+query.getText()+"</font></center></html>"); 
      panel.removeAll(); 
      panel.add(introLabel,BorderLayout.NORTH); 
      panel.add(panel1); 
     } 



     public void showTables(){ 
      String[] columnNames = {"TABLE NAME", 
      "BLAH"}; 


      Object[][] data = { 
      {"Table1", "PUBLIC"}, 
      {"Table2", "PUBLIC"} 
      }; 

      DefaultTableModel model = new DefaultTableModel(data,columnNames); 
      table.setModel(model); 
      tweakColumns(table); 
     } 
     /** 
     * makes the table and scrollpane at startup 
     * @throws SQLException 
     */ 
     public void displayTable() throws SQLException{ 

      table = new JTable(){ 
       private static final long serialVersionUID = 1L; 

       @Override 
        public boolean isCellEditable(int row, int column) { 
         return false; 
        } 

      }; 

      stable = new JScrollPane (table); 
      stable.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED); 
      stable.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED); 
      table.setAutoResizeMode(JTable.AUTO_RESIZE_OFF); 
      panel1.add(stable); 
      showTables(); 
     } 


     /** 
     * this resizes all the columns to make it clean 
     * @param table 
     */ 
     public static void tweakColumns(JTable table){ 
      Enumeration<TableColumn> columns = table.getColumnModel().getColumns(); 

      int required = 0; 
      while(columns.hasMoreElements()){ 
       TableColumn column = columns.nextElement(); 
       int width = (int)table.getTableHeader().getDefaultRenderer() 
          .getTableCellRendererComponent(table, column.getIdentifier() 
            , false, false, -1, column.getModelIndex()).getPreferredSize().getWidth(); 
       required += width; 
      } 

      JViewport viewport = (JViewport)SwingUtilities.getAncestorOfClass(JViewport.class, table); 
      int viewportWidth = viewport.getWidth(); 
      table.setAutoResizeMode(required<viewportWidth ? JTable.AUTO_RESIZE_ALL_COLUMNS : JTable.AUTO_RESIZE_OFF); 
     } 


     public static Component makeTextPanel(String text) { 
      JPanel panel = new JPanel(false); 
      JLabel filler = new JLabel(text); 
      filler.setHorizontalAlignment(JLabel.CENTER); 

      panel.add(filler); 
      return panel; 
     } 


} 

运行的是，你应该看到这个问题。为什么不在第一次运行时调整列大小？

Answer 1

表格第一次在屏幕上可见时，必须调用tweakColumns(table)。如低于此使用AncestorListener：

table.addAncestorListener(new AncestorListener(){ 
    @Override 
    public void ancestorAdded(AncestorEvent event){ 
     tweakColumns(table); 
    } 

    @Override 
    public void ancestorRemoved(AncestorEvent event){ 

    } 

    @Override 
    public void ancestorMoved(AncestorEvent event){ 

    } 
})