Question

我想在我的表格中创建自己的盒子。我做这个代码。但ComboBox没有出现（（

public class GUI {
    String RetVal1;
    String[][] RetValArr;
    private JFrame frame;
    private JLabel lblNewLabel;
    private JTextField Name_textField;

    private JFormattedTextField Phone_formattedTextField;


    static Connection conn3 = null;
    static int EC1;
    static int CurrentEntry;
    static String CurrentEntrySTR;

    private JTextField CurrentEnty_textField;
    private JTable table;

    public static void main(String[] args) {

        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    GUI window = new GUI();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });

    }
    public GUI() {
        initialize();
    }

    private void initialize() {

        frame = new JFrame();
        frame.setBounds(100, 100, 504, 513);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(null);

        JComboBox From_comboBox = new JComboBox();
        From_comboBox.setModel(new DefaultComboBoxModel(new String[] { "1", "2", "3", "4", "5" }));
        From_comboBox.setEditable(true);
        From_comboBox.setMaximumRowCount(2);
        From_comboBox.setBounds(274, 194, 186, 23);
        frame.getContentPane().add(From_comboBox);
        new ComboBoxDemo(frame);



        JComboBox Status_comboBox = new JComboBox();
        Status_comboBox.setBounds(274, 281, 186, 23);
        frame.getContentPane().add(Status_comboBox);

        CurrentEnty_textField = new JTextField();
    }
}

这是我自己的ComboBox的代码（（

public class ComboBoxDemo {

    private List<Country> countries;
    private JComboBox cBox;

    public ComboBoxDemo(JFrame frame) {
        countries = createCountryList();
        cBox = createComboBox(countries);
        frame.add(cBox);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    private JComboBox createComboBox(List<Country> countries) {
        final JComboBox comboBox = new JComboBox(countries.toArray());
        comboBox.setRenderer(new ComboBoxRenderer());
        comboBox.addItemListener(new ItemListener() {
            @Override
            public void itemStateChanged(ItemEvent e) {
                if (e.getStateChange() == ItemEvent.SELECTED) {
                    Country country = (Country) comboBox.getSelectedItem();
                    System.out.println(country.getIso());
                }
            }
        });
        return comboBox;
    }

    private class ComboBoxRenderer extends DefaultListCellRenderer {

        @Override
        public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected,
                boolean cellHasFocus) {
            JLabel label = (JLabel) super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
            Country country = (Country) value;
            label.setText(country.getName());
            return label;
        }
    }

    private List<Country> createCountryList() {
        List<Country> list = new ArrayList<>();
        list.add(new Country("Afghanistan", "AF"));
        list.add(new Country("Åland Islands", "AX"));
        list.add(new Country("Albania", "AL"));
        return list;
    }

    public class Country {
        private String name;
        private String iso;

        public Country(String name, String iso) {
            this.name = name;
            this.iso = iso;
        }

        public String getName() {
            return name;
        }

        public String getIso() {
            return iso;
        }
    }

}

但我无法在GUI表单中显示我的ComboBox。我需要从我的表单中调用它，但是，当我运行程序时 - 没有错误，但没有表单中的组合框...

Answer 1

首先使用null布局不是一个好主意。我认为你应该重新设计你的应用程序。请查看此讨论：why-is-it-frowned-upon-to-use-a-null-layout-in-swing

您的组合框未显示，因为在null布局中，所有组件都需要设置大小。您忘了setBounds()使用cBox。

无法在表单中显示自己的元素

1 个答案: