对话框中的 JComboBox

Question

我正在尝试根据员工的 ID 号码在对话框中显示组合框。当用户选择一个ID时，应用程序会显示该员工的数据。

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

    combo = new JComboBox(idNumbers);
        String[] options = { "OK", "Cancel"};

        int selection = JOptionPane.showOptionDialog(null, combo, "Search",
                JOptionPane.DEFAULT_OPTION, JOptionPane.PLAIN_MESSAGE, null,
                options, options[0]);
        if (selection > 0) {
             System.out.println("selection is: " + options[selection]);
          }
        currentItem = ((JComboBox)(e.getSource())).getSelectedIndex();
        displayDetails(currentItem);}
    });

结果我只有 null pointer exception。提前致谢！

堆栈跟踪：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at javax.swing.DefaultComboBoxModel.<init>(DefaultComboBoxModel.java:53)
    at javax.swing.JComboBox.<init>(JComboBox.java:175)
    at SearchId.initComponents(SearchId.java:37)
    at SearchId.<init>(SearchId.java:26)
    at EmployeeMenu.actionPerformed(EmployeeMenu.java:255)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
    at javax.swing.AbstractButton.doClick(AbstractButton.java:389)
    at javax.swing.plaf.basic.BasicMenuItemUI.doClick(BasicMenuItemUI.java:809)
    at com.apple.laf.AquaMenuItemUI.doClick(AquaMenuItemUI.java:137)
    at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(BasicMenuItemUI.java:850)
    at java.awt.Component.processMouseEvent(Component.java:6414)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3275)
    at java.awt.Component.processEvent(Component.java:6179)
    at java.awt.Container.processEvent(Container.java:2084)
    at java.awt.Component.dispatchEventImpl(Component.java:4776)
    at java.awt.Container.dispatchEventImpl(Container.java:2142)
    at java.awt.Component.dispatchEvent(Component.java:4604)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4618)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4279)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4209)
    at java.awt.Container.dispatchEventImpl(Container.java:2128)
    at java.awt.Window.dispatchEventImpl(Window.java:2492)
    at java.awt.Component.dispatchEvent(Component.java:4604)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:717)
    at java.awt.EventQueue.access0(EventQueue.java:82)
    at java.awt.EventQueue.run(EventQueue.java:676)
    at java.awt.EventQueue.run(EventQueue.java:674)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext.doIntersectionPrivilege(AccessControlContext.java:86)
    at java.security.AccessControlContext.doIntersectionPrivilege(AccessControlContext.java:97)
    at java.awt.EventQueue.run(EventQueue.java:690)
    at java.awt.EventQueue.run(EventQueue.java:688)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext.doIntersectionPrivilege(AccessControlContext.java:86)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:687)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

Answer 1

我认为您需要从变量 combo 中检索选定的索引。当用户选择一个项目时，您的组合中的选定项目会发生变化

所以选择：selected_index = combo.getSelectedIndex();

对话框中的 JComboBox

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