Java 边框内的JComboBox导致IllegalComponentStateException

我最近发现了这段有用的代码，用于创建一个有标题的边框，其中包含一个组件作为Santhosh Kumar T:的标题。我使用复选框成功地使用了它，但当我决定使用组合框时，它只显示组合框的文本部分，而不显示下拉按钮：

单击组合框时，出现以下异常：

Exception in thread "AWT-EventQueue-0" java.awt.IllegalComponentStateException: component must be showing on the screen to determine its location
at java.awt.Component.getLocationOnScreen_NoTreeLock(Unknown Source)
at java.awt.Component.getLocationOnScreen(Unknown Source)
at javax.swing.JPopupMenu.show(Unknown Source)
at javax.swing.plaf.basic.BasicComboPopup.show(Unknown Source)
at javax.swing.plaf.basic.BasicComboPopup.togglePopup(Unknown Source)
at javax.swing.plaf.basic.BasicComboPopup$Handler.mousePressed(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 test.ComponentTitledBorder.dispatchEvent(ComponentTitledBorder.java:74)
at test.ComponentTitledBorder.mousePressed(ComponentTitledBorder.java:96)
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$200(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)

我查看了所有我能找到的谷歌搜索结果，但没有一个能帮助我理解我的具体问题。为了说明，我提供了一个sscce：

package test;

import java.awt.BorderLayout;
import java.awt.Dimension;

import javax.swing.DefaultComboBoxModel;
import javax.swing.JComboBox;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;

@SuppressWarnings("serial")
public class Problem extends JComponent {

    JPanel area = new JPanel();
    JComboBox<String> cb;

    public Problem() {
        area.setPreferredSize(new Dimension(100,100));
        String[] options = {"one", "two"};
        cb = new JComboBox<String>(new DefaultComboBoxModel<String>(options));
        cb.setEditable(false);
        cb.setSelectedIndex(0);

        this.setLayout(new BorderLayout());
        area.setBorder(new ComponentTitledBorder(cb, area, UIManager.getBorder("TitledBorder.border")));
        this.add(area, BorderLayout.CENTER);
    }

    public static void main(String[] args) {

        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new Problem());
                frame.pack();
                frame.setVisible(true);
            }
        });
    }
}

封装测试；
导入java.awt.BorderLayout；
导入java.awt.Dimension；
导入javax.swing.DefaultComboxModel；
导入javax.swing.JComboBox；
导入javax.swing.JComponent；
导入javax.swing.JFrame；
导入javax.swing.JPanel；
导入javax.swing.SwingUtilities；
导入javax.swing.UIManager；
@抑制警告（“串行”）
公共类问题扩展JComponent{
JPanel区域=新的JPanel（）；
JComboBox cb；
公共问题（）{
面积。设置首选尺寸（新尺寸（100100））；
字符串[]选项={“一”，“二”}；
cb=新的JComboBox（新的DefaultComboxModel（选项））；
cb.setEditable（假）；
cb.setSelectedIndex（0）；
此.setLayout（新的BorderLayout（））；
setboorder（新组件TitledBorder（cb，area，UIManager.getBorder（“TitledBorder.border”））；
添加（区域、边框布局、中心）；
}
公共静态void main（字符串[]args）{
SwingUtilities.invokeLater（新的Runnable（）{
@凌驾
公开募捐{
JFrame=新JFrame（）；
frame.setDefaultCloseOperation（JFrame.EXIT_ON_CLOSE）；
frame.add（新问题（））；
frame.pack（）；
frame.setVisible（true）；
}
});
}
}

---

请帮助我解决此问题，并希望了解错误的性质。

使用

BorderLayout

定义

JPanel

，并将

JComboBox

添加到面板中。然后将

ComponentTitleBorder

分配给面板，而不是直接分配给

JComboBox

更新：

JPanel p = new JPanel(); 
p.setLayout(new BorderLayout()); 
p.add(cb, BorderLayout.CENTER); 
area.setBorder(new ComponentTitledBorder(p, area,
      UIManager.getBorder("TitledBorder.border")));

---

我将代码更改为：

JPanel p=newjpanel（）；p、 setLayout（新的BorderLayout（））；p、 添加（cb，BorderLayout.CENTER）；setboorder（新组件TitledBorder（p，area，UIManager.getBorder（“TitledBorder.border”））但现在组合框甚至没有显示。不要在无法阅读的注释中发布代码。改为将其编辑到问题中。@AndrewThompson转到答案谢谢您格式化了仍然无用的信息。。）我发现作者自己也知道这个问题，正如你在这里看到的（隐藏在评论中），但这并不能解释为什么会发生错误。