java - 如何刷新 JFrame

Question

我知道有类似的问题，但我有一些不同的问题...

我想在单击按钮后删除 JFrame 的所有元素:

有效:

button.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent arg0)
    {
        frame.getContentPane().removeAll();
        frame.revalidate();
        frame.repaint();
    }
});

所有元素都消失了。但是在那之后我需要在这个 JFrame 上放置元素...在上面的这 3 行之后(frame.repaint() 下方)我调用方法 initialize(我调用的方法我在开始时创建了我的窗口):

private void initialize()
{
    frame = new JFrame();
    frame.setBounds(100, 100, 1454, 860);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().setLayout(null);

    JButton btnNewSubject = new JButton("New subject");
    btnNewSubject.setBounds(647, 788, 137, 23);
    frame.getContentPane().add(btnNewSubject);

    JButton btnRefresh = new JButton("Refresh");
    btnRefresh.setBounds(1339, 788, 89, 23);
    frame.getContentPane().add(btnRefresh);

    JLabel lblNewLabel = new JLabel("Subject");
    lblNewLabel.setBounds(235, 11, 75, 14);
    frame.getContentPane().add(lblNewLabel);

    JLabel lblOwner = new JLabel("Owner");
    lblOwner.setBounds(662, 11, 46, 14);
    frame.getContentPane().add(lblOwner);

    JLabel lblStatus = new JLabel("Status");
    lblStatus.setBounds(883, 11, 46, 14);
    frame.getContentPane().add(lblStatus);

    JLabel lblDateOfAdded = new JLabel("Date of added");
    lblDateOfAdded.setBounds(1104, 11, 116, 14);
    frame.getContentPane().add(lblDateOfAdded);
}

没有任何反应。 :( JFrame 仍然是空的。即使我调用 revalidate 和 repaint()。

怎么了？

Answer 1

您在这里的方法中创建了一个全新的 JFrame

frame = new JFrame();

并且您从不显示它，您从不对其调用 setVisible(true)，因此它将保持不可见状态。听起来好像您正在创建两个 JFrames 而没有意识到，您正在向第二个未显示的 JFrame 添加组件，但只显示第一个 JFrame，即没有新组件的那个。

更重要的是，您需要使用 CardLayout 来帮助您交换 JPanel View ，因为它正是为这种情况而构建的。此外，您的程序使用 null 布局和 setBounds(...) 会导致僵硬的 GUI 在一个系统上看起来不错，但在任何其他系统或屏幕分辨率上通常看起来很差。以这种方式创建的程序很难调试、维护和升级。而是使用布局管理器，因为这是他们擅长的:创建可以轻松增强和更改的复杂灵活的 GUI。

请注意，您的 removeAll() 调用不会像 Ludovic 所说的那样删除根 Pane ，因为您是在 contentPane 而不是 JFrame 上调用它，并且 contentPane 不包含根 Pane 。

---

编辑
例如，

import java.awt.BorderLayout;
import java.awt.CardLayout;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;

import javax.swing.*;
import javax.swing.table.DefaultTableModel;

public class CardLayoutEg extends JPanel {
   private CardLayout cardlayout = new CardLayout();
   private TitlePanel titlePanel = new TitlePanel(this);
   private SubjectPanel subjectPanel = new SubjectPanel(this);

   public CardLayoutEg() {
      setLayout(cardlayout);
      add(titlePanel, titlePanel.getName());
      add(subjectPanel, subjectPanel.getName());
   }

   public void nextCard() {
      cardlayout.next(this);
   }

   public void showCard(String key) {
      cardlayout.show(this, key);
   }

   private static void createAndShowGui() {
      JFrame frame = new JFrame("CardLayout Example");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(new CardLayoutEg());
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }

}

class TitlePanel extends JPanel {
   public static final String TITLE_PANEL = "title panel";
   private static final int PREF_W = 900;
   private static final int PREF_H = 750;
   private static final String TITLE = "My Application Title";
   private static final float POINTS = 46f;
   private CardLayoutEg cardLayoutEg;

   public TitlePanel(CardLayoutEg cardLayoutEg) {
      setName(TITLE_PANEL);
      this.cardLayoutEg = cardLayoutEg;

      JLabel titleLabel = new JLabel(TITLE, SwingConstants.CENTER);
      titleLabel.setFont(titleLabel.getFont().deriveFont(Font.BOLD, POINTS));

      JButton subjectButton = new JButton(new SubjectAction("Subjects"));
      JPanel buttonPanel = new JPanel();
      buttonPanel.add(subjectButton);

      setLayout(new BorderLayout());
      add(titleLabel, BorderLayout.CENTER);
      add(buttonPanel, BorderLayout.PAGE_END);
   }

   @Override
   public Dimension getPreferredSize() {
      if (isPreferredSizeSet()) {
         return super.getPreferredSize();
      }
      return new Dimension(PREF_W, PREF_H);
   }

   private class SubjectAction extends AbstractAction {
      public SubjectAction(String name) {
         super(name);
         int mnemonic = (int) name.charAt(0);
         putValue(MNEMONIC_KEY, mnemonic);
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         cardLayoutEg.showCard(SubjectPanel.SUBJECT_PANEL);
      }
   }
}

class SubjectPanel extends JPanel {
   public static final String SUBJECT_PANEL = "subject panel";
   private static final String[] COLUMN_NAMES = {"Subject", "Owner", "Status", "Date Added"};
   DefaultTableModel tableModel = new DefaultTableModel(COLUMN_NAMES, 10);
   private JTable table = new JTable(tableModel);
   private CardLayoutEg cardLayoutEg;

   public SubjectPanel(CardLayoutEg cardLayoutEg) {
      setBorder(BorderFactory.createTitledBorder("Subject Panel"));
      setName(SUBJECT_PANEL);
      this.cardLayoutEg = cardLayoutEg;

      JPanel buttonPanel = new JPanel();
      buttonPanel.setLayout(new GridLayout(1, 0, 10, 0));
      buttonPanel.add(new JButton("New Subject"));
      buttonPanel.add(new JButton("Refresh"));
      buttonPanel.add(new JButton(new TitleAction("Title")));
      buttonPanel.add(new JButton(new ExitAction("Exit")));

      JPanel bottomPanel = new JPanel();
      bottomPanel.setLayout(new BoxLayout(bottomPanel, BoxLayout.LINE_AXIS));
      bottomPanel.add(Box.createHorizontalGlue());
      bottomPanel.add(buttonPanel);

      setLayout(new BorderLayout());
      add(new JScrollPane(table), BorderLayout.CENTER);
      add(bottomPanel, BorderLayout.PAGE_END);
   }

   private class TitleAction extends AbstractAction {
      public TitleAction(String name) {
         super(name);
         int mnemonic = (int) name.charAt(0);
         putValue(MNEMONIC_KEY, mnemonic);
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         cardLayoutEg.showCard(TitlePanel.TITLE_PANEL);
      }
   }

   private class ExitAction extends AbstractAction {
      public ExitAction(String name) {
         super(name);
         int mnemonic = KeyEvent.VK_X;
         putValue(MNEMONIC_KEY, mnemonic);
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         Component component = (Component) e.getSource();
         Window win = SwingUtilities.getWindowAncestor(component);
         win.dispose();
      }
   }
}