java - 交换 JComboBox 选择

Question

我有 2 个 JComboBox，填充了相同的条目(来自 ENUM 列表) 我有所选项目更改时的操作事件，但我们有我不太明白的要求。

代码正在转换货币...如果 Box1 = USD 且 Box2 = EURO，然后我将 Box1 更改为 = ERUO，我需要 Box2 更改为 = USD。下面是我的actionListeners

        fromCombo.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            String finalAmt = convertCurr(fromField.getText(),
                fromCombo.getSelectedItem().toString(),
                toCombo.getSelectedItem().toString());

            //Check for Errors
            try {
                Double.parseDouble(finalAmt);

                //CHANGE LABELS
                toLabel.setText(finalAmt + " " +
                    toCombo.getSelectedItem().toString());

                toField.setText(String.valueOf(finalAmt));
            } catch (NumberFormatException  nfe) {
                fromLabel.setText(finalAmt);

                toLabel.setText(finalAmt);

                toField.setText(finalAmt);
            } finally {
                fromLabel.setText(fromField.getText() + " " +
                    fromCombo.getSelectedItem().toString() + " equals");
            }

        }
    });

    toCombo.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            String finalAmt = convertCurr(fromField.getText(),
                fromCombo.getSelectedItem().toString(),
                toCombo.getSelectedItem().toString());

            //Check for Errors
            try {
                Double.parseDouble(finalAmt);

                //CHANGE LABELS
                toLabel.setText(finalAmt + " " +
                    toCombo.getSelectedItem().toString());

                toField.setText(String.valueOf(finalAmt));
            } catch (NumberFormatException  nfe) {
                fromLabel.setText(finalAmt);

                toLabel.setText(finalAmt);

                toField.setText(finalAmt);
            } finally {
                fromLabel.setText(fromField.getText() + " " +
                    fromCombo.getSelectedItem().toString() + " equals");
            }
        }
    });
    fromField.postActionEvent();

谁能帮我解决这个问题吗？需要更多信息吗？

编辑:这是一个精简后的示例代码库。

public class tDropDowns extends JPanel implements ActionListener {

private final JComboBox<CurrencyConstant> fromCombo;
private final JComboBox<CurrencyConstant> toCombo;

public tDropDowns() {
    fromCombo = new JComboBox<>(CurrencyConstant.values());
    fromCombo.setName("fromCombo");

    toCombo = new JComboBox<>(CurrencyConstant.values());
    toCombo.setName("toCombo");

    // TODO: Layout code goes here...
    JPanel entryFields = new JPanel();
    entryFields.setLayout(new GridBagLayout());
    //entryFields.setBorder(new EmptyBorder(10, 10, 10, 10));
    entryFields.setAlignmentX(Component.LEFT_ALIGNMENT);
    GridBagConstraints gbc = new GridBagConstraints();
    gbc.insets = new Insets(5, 10, 5, 10);

    gbc.gridx = 0;
    gbc.gridy = 0;
    entryFields.add(fromCombo, gbc);

    gbc.gridx = 0;
    gbc.gridy = 1;
    entryFields.add(toCombo, gbc);

    this.add(entryFields);

    // Set initial values:
    fromCombo.setSelectedItem(CurrencyConstant.USD);
    toCombo.setSelectedItem(CurrencyConstant.EUR);

    fromCombo.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {

        }
    });

    toCombo.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {

        }
    });
}

@Override
public void actionPerformed(ActionEvent arg0)
{

}

public static void createAndShowGUI() {
    JFrame frame = new JFrame("Currency Converter Dropdowns");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setMinimumSize(new Dimension(300, 150));
    JComponent newContentPane = new tDropDowns();
    newContentPane.setLayout(new BoxLayout(newContentPane,
        BoxLayout.PAGE_AXIS));
    newContentPane.setOpaque(true);
    frame.setContentPane(newContentPane);
    frame.pack();
    frame.setResizable(false);
    frame.setVisible(true);
}

public static void main(String[] args) {
    SwingUtilities.invokeLater(tDropDowns::createAndShowGUI);
}

}

Answer 1

感谢您的详细帖子。这是您问题的解决方案。我对每个应用的三元运算符添加了注释，以便清楚地说明代码在这里的作用。

您要做的就是找出您当前在单击的组合框中设置的货币是什么。然后在另一个框中设置相反的货币。我用三元运算符解决了这个问题。

    // Set initial values:
    fromCombo.setSelectedItem(CurrencyConstant.USD);
    toCombo.setSelectedItem(CurrencyConstant.EUR);

    fromCombo.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            toCombo.setSelectedItem(
                // Is EUR in fromCombo selected? Then set USD in toCombo. Else set EUR in toCombo.
                (fromCombo.getSelectedItem() == CurrencyConstant.EUR) ? CurrencyConstant.USD : CurrencyConstant.EUR

            );
        }
    });

    toCombo.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            fromCombo.setSelectedItem(
                // Is EUR in toCombo selected? Then set USD in fromCombo. Else set EUR in fromCombo.
                (toCombo.getSelectedItem() == CurrencyConstant.EUR) ? CurrencyConstant.USD : CurrencyConstant.EUR

            );
        }
    });

您现在可以添加触发货币计算等的其余代码。

希望这有帮助。