java - Swing :jlabel+jcombobox+jtextfield

Question

我需要在 jtextfield 旁边的 jcombobox 旁边构建一个 jlabel。 JTextfield 必须只接受数字。来自 jtextfield 的文本应该存储在一个字符串中，并且选择的元素也存储在一个不同的字符串中。如果我可以添加一个 jbutton 以便在单击按钮时解析所有选择，那将是理想的。我目前正在使用这个未完成的代码，但它不会工作。有人可以建议所需的补充吗？提前致谢

   public class constraints {

            private static JTextField tField;
            private MyDocumentFilter documentFilter;
            private JLabel amountLabel;
            private static String amountString = "Select Quantity (in ktones): ";
            public static String str = "" ;

            private void displayGUI()
            {
                JFrame frame = new JFrame("Constraints");
                frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

                amountLabel = new JLabel(amountString);

                JPanel contentPane = new JPanel();
                contentPane.setBorder(
                    BorderFactory.createEmptyBorder(5, 5, 5, 5));
                tField = new JTextField(10);

                amountLabel.setLabelFor(tField);

                String[] petStrings = { "Less", "Equal", "More"};
                JComboBox petList = new JComboBox(petStrings) ;
                        petList.setSelectedIndex(3);
                    petList.addActionListener(new ActionListener() {
                        public void actionPerformed(ActionEvent event) {

                             JComboBox cb = (JComboBox)event.getSource();
                             String petName = (String)cb.getSelectedItem();

                            System.out.println("petName");
                        }
                    });                         

                ((AbstractDocument)tField.getDocument()).setDocumentFilter(
                        new MyDocumentFilter());        
                contentPane.add(amountLabel);
                  contentPane.add(petList);
                contentPane.add(tField); 


                frame.setContentPane(contentPane);
                frame.pack();
                frame.setLocationByPlatform(true);
                frame.setVisible(true);
            }

            public static void main(String[] args)
            {
                Runnable runnable = new Runnable()
                {
                    @Override
                    public void run()
                    {
                        new constraints().displayGUI();
                    }
                };
                EventQueue.invokeLater(runnable);

            }
        }

        class MyDocumentFilter extends DocumentFilter
        {   
            @Override
            public void insertString(DocumentFilter.FilterBypass fp
                    , int offset, String string, AttributeSet aset)
                                        throws BadLocationException
            {
                int len = string.length();
                boolean isValidInteger = true;

                for (int i = 0; i < len; i++)
                {
                    if (!Character.isDigit(string.charAt(i)))
                    {
                        isValidInteger = false;
                        break;
                    }
                }
                if (isValidInteger)
                    super.insertString(fp, offset, string, aset);
                else
                    Toolkit.getDefaultToolkit().beep();
            }

            @Override
            public void replace(DocumentFilter.FilterBypass fp, int offset
                            , int length, String string, AttributeSet aset)
                                                throws BadLocationException
            {
                int len = string.length();
                boolean isValidInteger = true;

                for (int i = 0; i < len; i++)
                {
                    if (!Character.isDigit(string.charAt(i)))
                    {
                        isValidInteger = false;
                        break;
                    }
                }
                if (isValidInteger)
                    super.replace(fp, offset, length, string, aset);
                else
                    Toolkit.getDefaultToolkit().beep();
            }
        }

Answer 1

一些事情:

String[] petStrings = { "Less", "Equal", "More"};
JComboBox petList = new JComboBox(petStrings);
petList.setSelectedIndex(3);

这将抛出 java.lang.IllegalArgumentException: setSelectedIndex: 3 out of bounds 因为你的 JComboBox 只有 3 个项目(索引从 0 开始)。

String petName = (String)cb.getSelectedItem();
System.out.println("petName");

这将始终打印“petName”字符串。我想你想要:

System.out.println(petName);

无论如何，我认为你会想使用 ItemListener 而不是 ActionListener:

petList.addItemListener(new ItemListener() {
    @Override
    public void itemStateChanged(ItemEvent event) {
        JComboBox cb = (JComboBox)event.getSource();
        String petName = (String) cb.getSelectedItem();
        System.out.println(petName);
    }
});

更新

I need to only do that when a jbutton is clicked or enter. Is that possible?

是的。只需将 JComboBox 设置为最终版，然后将 JButton 添加到 JPanel 即可:

final JComboBox petList = new JComboBox(petStrings);
petList.setSelectedIndex(2);

JButton submit = new JButton("Submit");
submit.addActionListener(new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent e) {
        String petName = (String) petList.getSelectedItem();
        System.out.println(petName);
    }
});

PS:请注意，如果您不将 petList 设为 final，它将无法在 JButton 的 ActionListener 中访问