Java Swing GUI組合框問題

-1

我在使用我的swing GUI時遇到了一個奇怪的問題。我正在嘗試刷新按鈕清除組合框列表以刷新組件。它不工作，我可能只是犯了一個愚蠢的錯誤。這裏是我的代碼：Java Swing GUI組合框問題

public class GUI2 extends JFrame implements ActionListener { 

/** 
* 
*/ 
private JPanel contentPane; 
public JComboBox combobox; 
public ReadJoystick stick; 
private JButton refresh; 
/** 
* Launch the application. 
*/ 
public static void main(String[] args) { 
    EventQueue.invokeLater(new Runnable() { 
     public void run() { 
      try { 
       GUI2 frame = new GUI2(); 
       frame.setVisible(true); 
      } catch (Exception e) { 
       e.printStackTrace(); 
      } 
     } 
    }); 
} 

/** 
* Create the frame. 
*/ 
public GUI2() { 
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    setBounds(100, 100, 450, 300); 
    contentPane = new JPanel(); 
    contentPane.setLayout(new BorderLayout(0, 0)); 
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5)); 
    setContentPane(contentPane); 
    StickWidget Left = new StickWidget(); 
    Left.setName("Left Stick"); 
    contentPane.add(Left.draw(), BorderLayout.WEST); 
    StickWidget Right = new StickWidget(); 
    Right.setName("Right Stick"); 
    contentPane.add(Right.draw(), BorderLayout.EAST); 

    JPanel panel = new JPanel(); 
    contentPane.add(panel, BorderLayout.CENTER); 
    panel.setLayout(new BorderLayout(0, 0)); 

    JPanel panel_1 = new JPanel(); 
    panel.add(panel_1, BorderLayout.NORTH); 
    ReadJoystick stick = new ReadJoystick(); 
    JComboBox combobox = new JComboBox<Object>(stick.read().toArray()); 
    combobox.setPrototypeDisplayValue("XXXXXXX"); 
    panel_1.add(combobox); 
    JButton btnRefresh = new JButton("Refresh"); 
    btnRefresh.addActionListener(this); 
    panel_1.add(btnRefresh); 
} 

public void actionPerformed(ActionEvent e) { 
    combobox.removeAll(); 
    } 
}

此代碼當前讀取計算機可用的操縱桿並將它們顯示在組合框列表中。下面是我目前的GUI的一個畫面：

Screenshot of my GUI

我每次按下刷新按鈕，它拋出這個錯誤：

typeException in thread "AWT-EventQueue-0" java.lang.NullPointerException 
at xxxxxxxx.xxxxxx.xxxxxx.GUI2.actionPerformed(GUI2.java:74) 
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018) 
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341) 
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402) 
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259) 
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252) 
at java.awt.Component.processMouseEvent(Component.java:6516) 
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321) 
at java.awt.Component.processEvent(Component.java:6281) 
at java.awt.Container.processEvent(Container.java:2229) 
at java.awt.Component.dispatchEventImpl(Component.java:4872) 
at java.awt.Container.dispatchEventImpl(Container.java:2287) 
at java.awt.Component.dispatchEvent(Component.java:4698) 
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:4698) 
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:747) 
at java.awt.EventQueue.access$300(EventQueue.java:103) 
at java.awt.EventQueue$3.run(EventQueue.java:706) 
at java.awt.EventQueue$3.run(EventQueue.java:704) 
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:720) 
at java.awt.EventQueue$4.run(EventQueue.java:718) 
at java.security.AccessController.doPrivileged(Native Method) 
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) 
at java.awt.EventQueue.dispatchEvent(EventQueue.java:717) 
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)

來源

2015-07-13 Dragongeek

[請嘗試搜索（http://stackoverflow.com/questions/12249336 /刪除，所有的項目，從-A-組合框式的Java） – alex2410

removeAll是從Container繼承的方法，其目的是刪除容器中包含的所有子組件......不是你想要做的。

相反，你可以使用combobox.setModel(null)或combobox.setModel(new DefaultComboBoxModel())這將改變數據/模型這是支持組合框前面的空版本

鞦韆背上很多的它與一個獨立的「模型」，這使得它易於部件轉出什麼是該NullPointerException從事實來的意見

顯示你已經陰影您combobox變量在構造函數

public GUI2() { 
    //... 
    JComboBox combobox = new JComboBox<Object>(stick.read().toArray());

這是離開類的實例字段null，而不是它應該只是閱讀

combobox = new JComboBox<Object>(stick.read().toArray());

看一看How to Use Combo Boxes更多細節

來源

2015-07-13 08:02:34 MadProgrammer

Java Swing GUI組合框問題

回答

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