java - GridLayout不通过按钮点击添加组件？

Question

虽然在程序启动时添加 JButton 组件，但稍后尝试通过例如添加一些按钮时它将不起作用。单击按钮。

也许只是一个语法问题。

可能是什么原因？

下面代码中的示例程序以 CardLayout 开始，可以通过单击按钮将其滚动到也有一个按钮的面板，每次单击应添加一个按钮。

  import java.awt.BorderLayout;
  import java.awt.CardLayout;
  import java.awt.Color;
  import java.awt.FlowLayout;
  import java.awt.GridLayout;
  import java.awt.event.ActionEvent;
  import java.awt.event.ActionListener;
  import java.text.ParseException;
  import java.util.logging.Level;
  import java.util.logging.Logger;
  import javax.swing.JButton;
  import javax.swing.JFrame;
  import javax.swing.JLabel;
  import javax.swing.JPanel;
  import javax.swing.JTextArea;
  import javax.swing.SwingUtilities;
  import javax.swing.UIManager;
  import javax.swing.UnsupportedLookAndFeelException;

  public class GridTest {

   JFrame f;
   BorderLayout bl;
   JPanel p;
   JPanel start;
   JPanel cbb;
   JPanel grid;
   JPanel board;
   CardLayout c;
   CardLayout cl;
   JTextArea ta2;
   JButton sb2;
   JButton bb2;
   JButton cb;
   JButton getButton;
   JLabel aCross;
   JLabel back;
   String controls = "Controls";
   String boardS = "Board";    

   public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
    public void run() {
      try {
           UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
          new GridTest().startApp();
      } catch (ClassNotFoundException ex) {
          Logger.getLogger(GridTest.class.getName()).log(Level.SEVERE, null, ex);
      } catch (InstantiationException ex) {
          Logger.getLogger(GridTest.class.getName()).log(Level.SEVERE, null, ex);
      } catch (IllegalAccessException ex) {
          Logger.getLogger(GridTest.class.getName()).log(Level.SEVERE, null, ex);
      } catch (UnsupportedLookAndFeelException ex) {
          Logger.getLogger(GridTest.class.getName()).log(Level.SEVERE, null, ex);
      } catch (ParseException ex) {
          Logger.getLogger(GridTest.class.getName()).log(Level.SEVERE, null, ex);
      }
  }
 }); 
}

   private void startApp() throws ParseException {
    c = new CardLayout();
    cl = new CardLayout();
    p = new JPanel(c);
    p.setOpaque(false);
    start = new JPanel();
    start.setLayout(new BorderLayout());
    board = new JPanel();
    board.setLayout(new BorderLayout());
    grid = new JPanel();
    grid.setLayout(new GridLayout(2,3));
    cbb = new JPanel();
    cbb.setLayout(new FlowLayout());
    cb = new JButton("Board");
    cb.addActionListener(new BoardListener());
    bb2 = new JButton("Back");
    bb2.addActionListener(new BackListener());
    getButton = new JButton("GetButton");
    getButton.addActionListener(new GetButtonListener());

    start.add(BorderLayout.NORTH, cb);
    start.add(BorderLayout.CENTER, new JLabel("Center"));
    start.setBackground(Color.WHITE);
    cbb.add(bb2);
    cbb.add(getButton);
    grid.add(new JButton("Button 1"));
    grid.setBackground(Color.BLACK);
    board.add(BorderLayout.NORTH, cbb);
    board.add(BorderLayout.CENTER, grid);

    p.add(start, controls);
    p.add(board, boardS);

    cl = (CardLayout)(p.getLayout());
    cl.first(p);

    f = new JFrame();
    f.getContentPane().add(p, BorderLayout.CENTER);
    f.setSize(450,550);
    f.setResizable(false);
    f.setVisible(true);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   }

   private class BackListener implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent ev) {
     cl.first(p);
    }   
   }

   private class BoardListener implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent ev) {
     cl.show(p, boardS);
    }   
   }

   private class GetButtonListener implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent ev) {
     grid.add(new JButton("Button 2")); //how to get this in the Grid ?
    }   
   }
  }

Answer 1

虽然添加了按钮，但 UI 并未更新。尝试添加以下行。

grid.revalidate();

所以你的 GetButtonListener 应该看起来像:

private class GetButtonListener implements ActionListener {
     @Override
     public void actionPerformed(ActionEvent ev) {
       grid.add(new JButton("Button 2")); //how to get this in the Grid ?
       grid.revalidate();
    }
}