java - JPanel 从窗口消失

Question

下面的SSCCE 是一个扩展JPanel 的类。 JPanel 是日历的基本轮廓(为简单起见，我将其简化)，它由 JButton 组件、一个 JLabel 和一个 JTable。当我将此框架添加到窗口(即 JDialog)时，它显示正常。但是，当我用它添加另一个组件时，它就消失了。为什么会发生这种情况，我怎样才能避免这种情况发生？

import javax.swing.*;
import javax.swing.table.*;
import java.awt.*;

public class CalendarPanel extends JPanel {

    private static JDialog dialog = new JDialog();

    public static void main(String[] args) {

    setDialogProperties();
    addComponentsToDialog();
    dialog.setVisible(true);
    }

    private static void setDialogProperties() {
    dialog.setModal(true);
    dialog.setResizable(false);
    dialog.setSize(new Dimension(330, 400));
    dialog.setDefaultCloseOperation(2);
    dialog.setLocationRelativeTo(null);
    }

    private static void addComponentsToDialog() {
    CalendarPanel calendar = new CalendarPanel();
    JPanel panel = new JPanel();
    panel.add(calendar);

    dialog.add(panel);
    //dialog.add(new JLabel("Hello"));
    }

    private static final long serialVersionUID = 1L;
    private JLabel lblMonth;
    private JButton btnPrev, btnNext;
    private JTable tblCalendar;
    private DefaultTableModel mtblCalendar;
    private JScrollPane stblCalendar;
    private static GridBagLayout gridBag = new GridBagLayout();
    private GridBagConstraints constraints = new GridBagConstraints();

    public CalendarPanel() {

    super(gridBag);

    createControls();
    addControlsToPanel();
    addHeaders();
    setTableProperties();
    }

    private void createControls() {
    lblMonth = new JLabel("January");
    btnPrev = new JButton("<");
    btnNext = new JButton(">");
    mtblCalendar = new DefaultTableModel() {

        public boolean isCellEditable(int rowIndex, int mColIndex) {
        return false;
        }
    };
    tblCalendar = new JTable(mtblCalendar);
    stblCalendar = new JScrollPane(tblCalendar);
    stblCalendar.setPreferredSize(new Dimension(300, 247));
    }

    private void addControlsToPanel() {
    GridBagLayout topGridBag = new GridBagLayout();

    JPanel topPanel = new JPanel(topGridBag);

    JPanel labelPanel = new JPanel();
    labelPanel.add(lblMonth);
    labelPanel.setPreferredSize(new Dimension(180, 20));

    constraints.gridx = 1;
    topGridBag.setConstraints(labelPanel, constraints);

    constraints.gridx = 2;
    topGridBag.setConstraints(btnNext, constraints);

    topPanel.add(btnPrev);
    topPanel.add(labelPanel);
    topPanel.add(btnNext);

    gridBag.setConstraints(topPanel, constraints);

    constraints.gridy = 1;
    gridBag.setConstraints(stblCalendar, constraints);

    this.add(topPanel);
    this.add(stblCalendar);
    }

    private void addHeaders() {
    String[] headers = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };
    for (int i = 0; i < 7; i++) {
        mtblCalendar.addColumn(headers[i]);
    }
    }

    private void setTableProperties() {
    tblCalendar.getTableHeader().setReorderingAllowed(false);

    tblCalendar.setRowHeight(38);
    mtblCalendar.setColumnCount(7);
    mtblCalendar.setRowCount(6);
    }
}

Answer 1

默认情况下，JDialogs 和所有顶层窗口都使用 BorderLayout。当你在没有指定位置的情况下向它添加一个组件(实际上是它的 contentPane)时，你默认将它添加到 BorderLayout.CENTER 位置。每当您添加一个新组件时，您都会覆盖之前添加的组件。您需要了解可供您使用的布局，然后充分利用它们。

例如，

  dialog.add(panel);
  dialog.add(new JLabel("Hello", SwingConstants.CENTER), BorderLayout.SOUTH);
}

接下来您要避免设置任何大小，并确保 pack() 您的顶层窗口允许这样做。