java - gridbaglayout 将第二个项目放在中心

Question

正在制作一个应用程序，我想在其中添加文本字段到滚动 Pane ，正在使用GridBagLayout，遇到的问题是我添加的第一个文本字段添加在滚动 Pane 的顶部滚动 Pane 内的面板，但是从第二个开始，它们被添加到中心，这是我的代码:

public class main extends javax.swing.JFrame {
private static HashMap<String, Integer> anch_codes = new HashMap<String, Integer>();
private static List<Component> items = new ArrayList<>();
/**
 * Creates new form main

 */
public main() {
    initComponents();
}
/**
 * This method is called from within the constructor to initialize the form.
 * WARNING: Do NOT modify this code. The content of this method is always
 * regenerated by the Form Editor.
 */
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents() {

    jMenuBar1 = new javax.swing.JMenuBar();
    jMenu1 = new javax.swing.JMenu();
    jMenuItem1 = new javax.swing.JMenuItem();
    jMenu2 = new javax.swing.JMenu();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

    jMenu1.setText("File");

    jMenuItem1.setAccelerator(javax.swing.KeyStroke.getKeyStroke(java.awt.event.KeyEvent.VK_S, java.awt.event.InputEvent.CTRL_MASK));
    jMenuItem1.setLabel("Save");
    jMenu1.add(jMenuItem1);
    jMenuItem1.getAccessibleContext().setAccessibleName("save_opt");

    jMenuBar1.add(jMenu1);

    jMenu2.setText("Edit");
    jMenuBar1.add(jMenu2);

    setJMenuBar(jMenuBar1);

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 1282, Short.MAX_VALUE)
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 703, Short.MAX_VALUE)
    );

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

/**
 * @param args the command line arguments
 */
public static void main(String args[]) {
    /* 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(main.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(main.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(main.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(main.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() {
            setAnchCodes();
            JFrame fmain = new main();

            fmain.setLayout(new GridBagLayout());
            GridBagConstraints c = new GridBagConstraints();

            fmain.setExtendedState(JFrame.MAXIMIZED_BOTH); 

            JTextField maintext = new JTextField();
            addToGrid(c, fmain, maintext, 0, 0, 0.9, 1.0, anch_codes.get("FIRST_LINE_START"));

            JButton add_btn =  new JButton("Add");
            addToGrid(c, fmain, add_btn, 1, 0, 0.1, 1.0, anch_codes.get("FIRST_LINE_START"));

            JPanel scrpanel = new JPanel(new GridBagLayout());
            scrpanel.setBackground(Color.WHITE);
            JScrollPane display_area = new JScrollPane(scrpanel);
            display_area.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
            display_area.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
            addToGrid(c, fmain, display_area, 0, 1, 1.0, 1000, anch_codes.get("FIRST_LINE_START"), 2);

            GridBagConstraints an_c = new GridBagConstraints();
            eventAddNew(an_c, add_btn,maintext,scrpanel,fmain,display_area);

            fmain.setVisible(true);

        }
    });
}

public static void eventAddNew(GridBagConstraints c, Component ... comp) {
    JButton add_btn = (JButton) comp[0];
    JTextField maintext = (JTextField) comp[1];
    JPanel scrpanel = (JPanel) comp[2];
    JFrame fmain = (JFrame) comp[3];
    JScrollPane display_area = (JScrollPane) comp[4];
    add_btn.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            JTextField item = new JTextField(maintext.getText());
            item.setEnabled(false);
            item.setEditable(false);
            addToGrid(c, scrpanel, item, 0, items.size(), 1.0, 1.0, anch_codes.get("FIRST_LINE_START"));
            items.add(item);
            fmain.repaint();
            fmain.revalidate();
            display_area.repaint();
            display_area.revalidate();
        }
    });
}

public static void addToGrid(GridBagConstraints c, Component parent, Component child, int x, int y, double weightx, double weighty, int anchor){

    String fcls = parent.getClass().toString();
    String cls = fcls.substring(fcls.lastIndexOf(".")+1);

    c.fill = GridBagConstraints.HORIZONTAL;
    c.anchor = anchor;
    c.weightx = weightx;
    c.weighty = weighty;
    c.gridx = x;
    c.gridy = y;

    if ("JFrame".equals(cls) || "main".equals(cls)) {
        JFrame frame = (JFrame) parent;
        frame.add(child,c);
    } else if ("JPanel".equals(cls)) {
        JPanel panel = (JPanel) parent;
        panel.add(child, c);
    }
}

public static void addToGrid(GridBagConstraints c, JFrame frame, Component element, int x, int y, double weightx, double weighty, int anchor, int gridwidth){

    String fcls = element.getClass().toString();
    String cls = fcls.substring(fcls.lastIndexOf(".")+1);


    c.anchor = anchor;
    c.weightx = weightx;
    c.weighty = weighty;
    c.gridx = x;
    c.gridy = y;
    c.gridwidth = gridwidth;
    if ("JScrollPane".equals(cls)) {
        c.fill = GridBagConstraints.BOTH;
    } else {
        c.fill = GridBagConstraints.HORIZONTAL;
    }
    frame.add(element,c);
}

private static void setAnchCodes() {
    anch_codes.put("FIRST_LINE_START", 23);
    anch_codes.put("FIRST_LINE_END", 24);
}

// Variables declaration - do not modify                     
private javax.swing.JMenu jMenu1;
private javax.swing.JMenu jMenu2;
private javax.swing.JMenuBar jMenuBar1;
private javax.swing.JMenuItem jMenuItem1;
// End of variables declaration                   
}

我对也有网格袋布局的外框架遇到了同样的问题，但我通过将权重设置为高值来解决这个问题，但这不适用于有问题的情况，并且可能不是正确的方法去做吧。如果有人能提供任何建议，那将会有很大帮助。

Answer 1

您不需要为此使用 GridBagLayout，我建议您不要这样做。相反，为具有 1 列和任意行数的网格创建一个使用 GridLayout(0, 1) 的 JPanel。然后——这是关键——将此 JPanel 放入另一个使用 BorderLayout 的 JPanel 中，放入 BorderLayout.PAGE_START 位置，以便它始终位于顶部。然后将这个使用 JPanel 的边框布局放入 JScrollPane 中。

例如:

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;

import javax.swing.*;

public class AddComponents extends JPanel {
    private static final int PREF_W = 600;
    private static final int PREF_H = 450;
    private JTextField inputField = new JTextField(20);
    private AddAction addAction = new AddAction("Add");
    private JButton addButton = new JButton(addAction);
    private JPanel innerPanel = new JPanel(new GridLayout(0, 1)); // 1 column, any number of rows

    public AddComponents() {
        JPanel borderLayoutPanel = new JPanel(new BorderLayout());
        borderLayoutPanel.add(innerPanel, BorderLayout.PAGE_START);
        JScrollPane scrollPane = new JScrollPane(borderLayoutPanel);
        scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

        inputField.setAction(addAction);
        JPanel topPanel = new JPanel();
        topPanel.setLayout(new BoxLayout(topPanel, BoxLayout.LINE_AXIS));
        topPanel.add(inputField);
        topPanel.add(addButton);

        setLayout(new BorderLayout());
        add(scrollPane);
        add(topPanel, BorderLayout.PAGE_START);
    }

    @Override
    public Dimension getPreferredSize() {
        Dimension prefSize = super.getPreferredSize();
        if (isPreferredSizeSet()) {
            return prefSize;
        } else {
            int w = Math.max(PREF_W, prefSize.width);
            int h = Math.max(PREF_H, prefSize.height);
            return new Dimension(w, h);
        }
    }

    private class AddAction extends AbstractAction {
        public AddAction(String name) {
            super(name);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            String text = inputField.getText();
            JTextField innerTextField = new JTextField(text);
            innerPanel.add(innerTextField);
            revalidate();
            repaint();
            inputField.selectAll();
            inputField.requestFocusInWindow();
        }
    }

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

    private static void createAndShowGui() {
        AddComponents mainPanel = new AddComponents();
        JFrame frame = new JFrame("Add Components");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(mainPanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}

但是在展示了这一点之后，如果您想显示 JTextField 等效项(根据您的需要，这些等效项可能是可编辑的，也可能是不可编辑的)，那么请使用简单的 JTable。

例如:

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.event.ActionEvent;

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

public class AddItems extends JPanel {
    private static final int PREF_W = 600;
    private static final int PREF_H = 450;
    private JTextField inputField = new JTextField(20);
    private AddToTableAction addAction = new AddToTableAction("Add");
    private JButton addButton = new JButton(addAction);
    private DefaultTableModel tableModel = new DefaultTableModel(new String[]{"A"}, 0);
    private JTable table = new JTable(tableModel){
        public boolean isCellEditable(int row, int column) {
            return false;
        };
    };

    public AddItems() {
        table.setTableHeader(null);
        JScrollPane scrollPane = new JScrollPane(table);
        scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

        inputField.setAction(addAction);
        JPanel topPanel = new JPanel();
        topPanel.setLayout(new BoxLayout(topPanel, BoxLayout.LINE_AXIS));
        topPanel.add(inputField);
        topPanel.add(addButton);

        setLayout(new BorderLayout());
        add(scrollPane);
        add(topPanel, BorderLayout.PAGE_START);
    }

    @Override
    public Dimension getPreferredSize() {
        Dimension prefSize = super.getPreferredSize();
        if (isPreferredSizeSet()) {
            return prefSize;
        } else {
            int w = Math.max(PREF_W, prefSize.width);
            int h = Math.max(PREF_H, prefSize.height);
            return new Dimension(w, h);
        }
    }

    private class AddToTableAction extends AbstractAction {
        public AddToTableAction(String name) {
            super(name);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            String text = inputField.getText();
            tableModel.addRow(new String[] {text});
            inputField.selectAll();
            inputField.requestFocusInWindow();
        }
    }

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

    private static void createAndShowGui() {
        AddItems mainPanel = new AddItems();
        JFrame frame = new JFrame("AddItems");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }
}