如何解決此錯誤“java.lang.ClassCastException: javax.swing.JList$3 無法轉換為 javax.swing.DefaultListModel”

Question

我從下拉列表中獲取選定的值並添加到 jlist 中。 但是我只收到我的字段（日期選擇器字段和另一個組合框字段）的這個錯誤。 我初始化並使用了默認列表模型。 每次在添加之前我都會清除我的清單。 但是當我在組合框中選擇一個值時，它顯示錯誤為

4 Mar, 2014 7:39:23 AM adminscreen.taskallocationscreennew t_dateActionPerformed
SEVERE: null
java.lang.ClassCastException: javax.swing.JList$3 cannot be cast to javax.swing.DefaultListModel
    at adminscreen.taskallocationscreennew.t_dateActionPerformed(taskallocationscreennew.java:820)
    at adminscreen.taskallocationscreennew.access$600(taskallocationscreennew.java:50)
    at adminscreen.taskallocationscreennew$7.actionPerformed(taskallocationscreennew.java:579)
    at org.jdesktop.swingx.JXDatePicker.fireActionPerformed(JXDatePicker.java:876)
    at org.jdesktop.swingx.JXDatePicker.commitEdit(JXDatePicker.java:706)
    at org.jdesktop.swingx.plaf.basic.BasicDatePickerUI.commit(BasicDatePickerUI.java:901)
    at org.jdesktop.swingx.plaf.basic.BasicDatePickerUI$Handler.monthViewActionPerformed(BasicDatePickerUI.java:1374)
    at org.jdesktop.swingx.plaf.basic.BasicDatePickerUI$Handler.actionPerformed(BasicDatePickerUI.java:1349)
    at org.jdesktop.swingx.JXMonthView.fireActionPerformed(JXMonthView.java:1797)
    at org.jdesktop.swingx.JXMonthView.commitSelection(JXMonthView.java:1695)
    at org.jdesktop.swingx.plaf.basic.BasicMonthViewUI$Handler.mouseReleased(BasicMonthViewUI.java:2075)
    at java.awt.Component.processMouseEvent(Component.java:6267)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
    at java.awt.Component.processEvent(Component.java:6032)
    at java.awt.Container.processEvent(Container.java:2041)
    at java.awt.Component.dispatchEventImpl(Component.java:4630)
    at java.awt.Container.dispatchEventImpl(Container.java:2099)
    at java.awt.Component.dispatchEvent(Component.java:4460)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
    at java.awt.Container.dispatchEventImpl(Container.java:2085)
    at java.awt.Window.dispatchEventImpl(Window.java:2478)
    at java.awt.Component.dispatchEvent(Component.java:4460)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

下面是我的代碼：

   private void d_pagetypeActionPerformed(java.awt.event.ActionEvent evt)          {                                           
    // TODO add your handling code here:
   System.out.println("d_pagetype"+d_pagetype.getSelectedItem());

   try {

            if(l_storieslist.getModel() != null)
            {
        ((DefaultListModel) l_storieslist.getModel()).clear();
        listf(directoryName);
            }

            else
            {
            }
    } catch (Exception ex) {
        Logger.getLogger(taskallocationscreennew.class.getName()).log(Level.SEVERE, null, ex);
    }
    l_storieslist.setModel(fileNameList);
    l_storieslist.setBackground(Color.WHITE);

}

Answer 1

在以下行中：

l_storieslist.setModel(fileNameList);

fileNameList 是 JList 的實例，它應該是 DefaultListModel 的實例。

可能您不需要再次設置模型。 而是在現有模型上進行操作。 您可以像在代碼中一樣獲取對現有模型的引用

ListModel model = l_storieslist.getModel();

並執行添加/刪除您想要的任何列表項的操作。

Answer 2

模型應該在 List 初始化時設置（ 在這里發現）

默認情況下，它使用內部類 impl 作為模型，您需要在構建列表時顯式設置 DefaultListModel！