如何仅从 Swing 中的多个 JList 中选择一项答案

【问题标题】：How to only select one item from a number of JLists in Swing如何仅从 Swing 中的多个 JList 中选择一项
【发布时间】：2014-01-30 21:23:23
【问题描述】：

所以我有一个 GUI，可以在创建类别时创建 Jlist。我只希望用户一次能够从任何 jlist 中选择一项。我还在检索有关所选项目的信息，例如它在链接列表中的位置。然而，到目前为止，我的代码出现了一个错误，但它似乎并没有影响功能，想知道是否有人可以帮助我解决为什么或如何解决它？

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);
             }
        });
}

而出现的错误是：

'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？提前致谢。

【问题讨论】：

您应该始终指出异常指向的行。 57 是哪一行？
啊，对不起，第 57 行是 String selectedString = (jList.getSelectedValue().toString());第 54 行是 jList.clearSelection();

标签： java swing selection jlist

【解决方案1】：

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

看起来这一行抛出了异常。

您在同一个侦听器中清除选择，然后它会调用选择更改。

尝试将获取的值移到jList.clearSelection()之前。

我还将引入一个标志来显示用户单击或清除选择的代码中的选择更改。将标志 isMyCode 设置为 true（默认为 false），如果为 true，则跳过处理。

【讨论】：