java - 我试图在单击时将 JPanel 添加到我的 JFrame，但我没有发现我的错误

Question

我正在努力恢复一些 Java 技能，因为我在网络开发方面工作了很长时间。现在我只是创建一个主 Jframe，其中有一个小菜单和一个扩展 JPanel 的类 createSchueler。

那么如果你进入菜单点击 Neu > Schueler 我想做什么

应创建一个新的 Jpanel 并将其添加到窗口

主类

public class MainWindow {

private JFrame frame;


/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                MainWindow window = new MainWindow();
                window.frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the application.
 */
public MainWindow() {
    initialize();
}

/**
 * Initialize the contents of the frame.
 */
private void initialize() {
    frame = new JFrame();
    frame.setBounds(100, 100, 807, 541);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().setLayout(null);

    JPanel createSchueler = new createSchueler();

    JMenuBar menuBar = new JMenuBar();
    frame.setJMenuBar(menuBar);

    JMenu mnNewMenu = new JMenu("Neu");
    mnNewMenu.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent arg0) {
            createSchueler.setVisible(true);
            frame.getContentPane().add(createSchueler);

        }
    });
    menuBar.add(mnNewMenu);

    JMenuItem mntmSchler = new JMenuItem("Sch\u00FCler");
    mnNewMenu.add(mntmSchler);

    JMenu mnBearbeiten = new JMenu("Bearbeiten");
    menuBar.add(mnBearbeiten);

    JMenuItem mntmSchler_1 = new JMenuItem("Sch\u00FCler");
    mnBearbeiten.add(mntmSchler_1);


  }
}

createSchueler 类扩展了我想添加到框架中的 JPanel

public class createSchueler extends JPanel {
private JTextField textField;
private JTextField textField_1;
private JTextField textField_2;

/**
 * Create the panel.
 */
public createSchueler() {
    setLayout(null);

    JLabel lblNeuenSchuelerErstellen = new JLabel("Neuen Schueler erstellen");
    lblNeuenSchuelerErstellen.setFont(new Font("Tahoma", Font.PLAIN, 22));
    lblNeuenSchuelerErstellen.setBounds(29, 27, 268, 27);
    add(lblNeuenSchuelerErstellen);

    JLabel lblVorname = new JLabel("Vorname");
    lblVorname.setBounds(29, 102, 46, 14);
    add(lblVorname);

    textField = new JTextField();
    textField.setBounds(97, 99, 172, 20);
    add(textField);
    textField.setColumns(10);

    JLabel lblNachname = new JLabel("Nachname");
    lblNachname.setBounds(29, 133, 69, 14);
    add(lblNachname);

    textField_1 = new JTextField();
    textField_1.setBounds(97, 130, 172, 20);
    add(textField_1);
    textField_1.setColumns(10);

    JLabel lblGeburtstag = new JLabel("Geburtstag");
    lblGeburtstag.setBounds(29, 169, 69, 14);
    add(lblGeburtstag);

    textField_2 = new JTextField();
    textField_2.setBounds(97, 166, 172, 20);
    add(textField_2);
    textField_2.setColumns(10);

    ButtonGroup bg = new ButtonGroup();

    JRadioButton rdbtnMnnlich = new JRadioButton("M\u00E4nnlich");
    rdbtnMnnlich.setBounds(29, 206, 69, 23);
    bg.add(rdbtnMnnlich);

    JRadioButton rdbtnWeiblich = new JRadioButton("Weiblich");
    rdbtnWeiblich.setBounds(97, 206, 109, 23);
    bg.add(rdbtnWeiblich);



   }
 }

希望一切都很重要:D

Answer 1

使用 CardLayout 交换 JPanel，而不是手动添加它们。如果您必须手动添加它们，请确保接收容器的布局管理器能够胜任该任务并且能够很好地处理添加。例如 BorderLayout 会接受它，但 GroupLayout 不会。如果您手动添加或删除，请在这些更改后对容器调用 revalidate(); 和 repaint()。

此外，您还在添加的 JPanel 和 contentPane 中使用了 null 布局，这将完全破坏它的 preferredSize 计算。永远不要使用这种布局。学习使用然后使用布局管理器。这是你的主要错误。

有关此的更多信息，请阅读:Why is it frowned upon to use a null layout in Swing?

例如:

import java.awt.CardLayout;
import java.awt.event.ActionEvent;
import javax.swing.*;

public class MainGui {
    public static final String SCHUELER_PANEL = "Schueler Panel";
    public static final String EMPTY = "Empty Panel";
    private JPanel mainPanel = new JPanel();
    private JMenuBar menuBar = new JMenuBar();
    private CardLayout cardLayout = new CardLayout();
    private SchuelerPanel schuelerPanel = new SchuelerPanel();


    public MainGui() {
        mainPanel.setLayout(cardLayout);
        mainPanel.add(new JLabel(), EMPTY); // empty label
        mainPanel.add(schuelerPanel, SCHUELER_PANEL);

        JMenu menu = new JMenu("Panel");
        menu.add(new JMenuItem(new SwapPanelAction(EMPTY)));
        menu.add(new JMenuItem(new SwapPanelAction(SCHUELER_PANEL)));
        menuBar.add(menu);
    }

    public JPanel getMainPanel() {
        return mainPanel;
    }

    public JMenuBar getMenuBar() {
        return menuBar;
    }

    @SuppressWarnings("serial")
    private class SwapPanelAction extends AbstractAction {
        public SwapPanelAction(String title) {
            super(title);
            int mnemonic = (int) title.charAt(0);
            putValue(MNEMONIC_KEY, mnemonic);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            cardLayout.show(mainPanel, (String) getValue(NAME));
        }
    }

    private static void createAndShowGui() {
        MainGui mainGui = new MainGui();
        JFrame frame = new JFrame("Main Gui");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(mainGui.getMainPanel());
        frame.setJMenuBar(mainGui.getMenuBar());
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}

和

import java.awt.BorderLayout;
import java.awt.Font;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.util.HashMap;
import java.util.Map;
import javax.swing.*;

@SuppressWarnings("serial")
public class SchuelerPanel extends JPanel {
    private static final String TITLE_TEXT = "Lorem Ipsum Dolor Sit Amet";
    public static final String[] LABEL_STRINGS = {"Monday", "Tuesday", "Wednesday"};
    private Map<String, JTextField> labelFieldMap = new HashMap<>();

    public SchuelerPanel() {
        JLabel titleLabel = new JLabel(TITLE_TEXT, JLabel.CENTER);
        titleLabel.setFont(new Font(Font.SANS_SERIF, Font.BOLD, 20));

        JPanel labelFieldPanel = new JPanel(new GridBagLayout());
        for (int i = 0; i < LABEL_STRINGS.length; i++) {
            addToPanel(labelFieldPanel, LABEL_STRINGS[i], i);
        }

        // Don't do what I'm doing here: avoid "magic" numbers!
        setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5)); 
        setLayout(new BorderLayout(10, 10));
        add(titleLabel, BorderLayout.PAGE_START);
        add(labelFieldPanel, BorderLayout.CENTER);
    }

    // get the text from the JTextField based on the JLabel associated with it
    public String getText(String labelText) {
        JTextField textField = labelFieldMap.get(labelText);
        if (textField == null) {
            throw new IllegalArgumentException("For labelText: " + labelText);
        }
        return textField.getText();
    }

    private void addToPanel(JPanel gblUsingPanel, String labelString, int row) {
        JLabel label = new JLabel(labelString);
        label.setFont(label.getFont().deriveFont(Font.BOLD));
        JTextField textField = new JTextField(10);
        labelFieldMap.put(labelString, textField);

        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridx = 0;
        gbc.gridy = row;
        gbc.anchor = GridBagConstraints.WEST;
        gbc.fill = GridBagConstraints.BOTH;
        gbc.weightx = 0.0;
        gbc.weighty = 0.0;
        gbc.insets = new Insets(5, 5, 5, 5);
        gblUsingPanel.add(label, gbc);

        gbc.gridx = 1;
        gbc.anchor = GridBagConstraints.EAST;
        gbc.fill = GridBagConstraints.HORIZONTAL;
        gblUsingPanel.add(textField, gbc);
    }

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

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}