在可编辑的JComboBox上调用getSelectedItem（）时出现NullPointerException

时间：2014-12-24 16:12:39

标签： java swing jcombobox keylistener

我有一个带有键监听器的可编辑组合框。我想在其中写入一些文本，并且每个字母都必须使用我插入（或删除）的文本创建一个字符串。 但是当我想得到字符串时，我得到NullPointerException。

combobox.getEditor().getEditorComponent()
    .addKeyListener(new KeyListener()
    {

        String value="";
        @Override
        public void keyTyped(KeyEvent e)
        {
            value = combobox.getSelectedItem().toString();
            System.out.println(value);
        }

        @Override
        public void keyReleased(KeyEvent e)
        {
        }

        @Override
        public void keyPressed(KeyEvent e)
        {

        }
    });

堆栈追踪：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at auftrag_paket.Neuer_Auftrag_ohneMwSt$25.keyTyped(Neuer_Auftrag_ohneMwSt.java:2037)
    at java.awt.Component.processKeyEvent(Unknown Source)
    at javax.swing.JComponent.processKeyEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.KeyboardFocusManager.redispatchEvent(Unknown Source)
    at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(Unknown Source)
    at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(Unknown Source)
    at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(Unknown Source)
    at java.awt.DefaultKeyboardFocusManager.dispatchEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$400(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.WaitDispatchSupport$2.run(Unknown Source)
    at java.awt.WaitDispatchSupport$4.run(Unknown Source)
    at java.awt.WaitDispatchSupport$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.awt.WaitDispatchSupport.enter(Unknown Source)
    at java.awt.Dialog.show(Unknown Source)
    at java.awt.Component.show(Unknown Source)
    at java.awt.Component.setVisible(Unknown Source)
    at java.awt.Window.setVisible(Unknown Source)
    at java.awt.Dialog.setVisible(Unknown Source)
    at auftrag_paket.Auftragsverwaltung$14.actionPerformed(Auftragsverwaltung.java:1865)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$400(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

有没有人有任何想法？

2 个答案:

答案 0 :(得分：1)

使用AWT时，请勿使用旧代码的KeyListener。 Swing有更新更好的API。

相反，您应该使用DocumentListener。有关更多信息，请阅读Swing教程中有关如何编写文档侦听器的部分。

答案 1 :(得分：0)

要使用KeyListener捕获在组合框中键入的任何字符，您应该在keyReleased方法中执行此操作，请尝试以下代码：

combobox.getEditor().getEditorComponent()
        .addKeyListener(new KeyListener()
        {

            String value="";
            @Override
            public void keyTyped(KeyEvent e)
            {

            }

            @Override
            public void keyReleased(KeyEvent e)
            {
                value = combo.getSelectedItem().toString();
                value = ((JTextField)combo.getEditor().getEditorComponent()).getText();
                System.out.println(value);
            }

            @Override
            public void keyPressed(KeyEvent e)
            {

            }
        });
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