Question

所以我有一个GUI，可以在创建类别时创建Jlists。我只希望用户能够一次从任何jlist中选择一个项目。我也正在检索有关所选项目的信息，例如它在链表中的位置。但是到目前为止，我的代码出现错误，但它似乎没有影响功能，想知道是否有人可以帮我解决原因或如何修复它？

这是我的代码：

public void addListener(final JList jList, final int curListCount) {
        jList.addListSelectionListener(new ListSelectionListener() {
            public void valueChanged(ListSelectionEvent evt) {
                jLabel2.setText("");
                if (isSelected == true) {
                    isSelected = false;
                    jList.clearSelection();
                    jLabel2.setText("");
                }
                String selectedString = (jList.getSelectedValue().toString());
                jLabel2.setText(selectedString);
                int selectedIndex = jList.getSelectedIndex();
                isSelected = true;
                System.out.println("Array position is: " + curListCount);
                System.out.println("LinkedList position is: " + selectedIndex);
             }
        });
}

出现的错误是：

'Array position is: 3 LinkedList position is: 0 Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at smartChart.wbt$1.valueChanged(wbt.java:57)
at javax.swing.JList.fireSelectionValueChanged(JList.java:1798)
at javax.swing.JList$ListSelectionHandler.valueChanged(JList.java:1812)
at javax.swing.DefaultListSelectionModel.fireValueChanged(DefaultListSelectionModel.java:184)
at javax.swing.DefaultListSelectionModel.fireValueChanged(DefaultListSelectionModel.java:164)
at javax.swing.DefaultListSelectionModel.fireValueChanged(DefaultListSelectionModel.java:211)
at javax.swing.DefaultListSelectionModel.changeSelection(DefaultListSelectionModel.java:405)
at javax.swing.DefaultListSelectionModel.changeSelection(DefaultListSelectionModel.java:415)
at javax.swing.DefaultListSelectionModel.removeSelectionIntervalImpl(DefaultListSelectionModel.java:576)
at javax.swing.DefaultListSelectionModel.clearSelection(DefaultListSelectionModel.java:420)
at javax.swing.JList.clearSelection(JList.java:2045)
at smartChart.wbt$1.valueChanged(wbt.java:54)
at javax.swing.JList.fireSelectionValueChanged(JList.java:1798)
at javax.swing.JList$ListSelectionHandler.valueChanged(JList.java:1812)
at javax.swing.DefaultListSelectionModel.fireValueChanged(DefaultListSelectionModel.java:184)
at javax.swing.DefaultListSelectionModel.fireValueChanged(DefaultListSelectionModel.java:154)
at javax.swing.DefaultListSelectionModel.setValueIsAdjusting(DefaultListSelectionModel.java:685)
at javax.swing.JList.setValueIsAdjusting(JList.java:2142)
at javax.swing.plaf.basic.BasicListUI$Handler.mouseReleased(BasicListUI.java:2796)
at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:290)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:694)
at java.awt.EventQueue$3.run(EventQueue.java:692)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:708)
at java.awt.EventQueue$4.run(EventQueue.java:706)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)'

有什么想法吗？提前谢谢。

Answer 1

String selectedString = (jList.getSelectedValue().toString());

看起来此行会引发异常。

您在同一个侦听器中清除选择，然后又调用选择更改。

尝试将获取值移到jList.clearSelection（）。

之前

此外，我还会介绍一个标志，以显示用户点击或代码中的选择更改，从而清除选择。将标志isMyCode设置为true（默认为false），如果为真，则跳过处理。

如何只从Swing中的多个JLists中选择一个项目

1 个答案: