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我試圖理解爲什麼下面的代碼不工作：爲什麼建築時JComboBox需要物品-1？
JComboBox status = new javax.swing.JComboBox();
status.setModel(new DefaultComboBoxModel() {
@Override
public void addElement(Object anObject) {
statusList.add((RequirementStatus) anObject);
super.addElement(anObject);
}
@Override
public int getSize() {
return statusList.size();
}
@Override
public Object getElementAt(int index) {
return index >= 0 && index < statusList.size()
? statusList.get(index) : null;
}
});
status.setRenderer(new ListCellRenderer() {
@Override
public Component getListCellRendererComponent(JList list,
Object value, int index, boolean isSelected,
boolean cellHasFocus) {
return index >= 0 ? new JLabel(
((RequirementStatus) ((ComboBoxModel) status.getModel())
.getElementAt(index)).getStatus())
: new JLabel("");
}
});
這一個作用：
JComboBox status = new javax.swing.JComboBox();
status.setModel(new DefaultComboBoxModel() {
@Override
public void addElement(Object anObject) {
statusList.add((RequirementStatus) anObject);
super.addElement(anObject);
}
@Override
public int getSize() {
return statusList.size();
}
@Override
public Object getElementAt(int index) {
return statusList.get(index);
}
});
status.setRenderer(new ListCellRenderer() {
@Override
public Component getListCellRendererComponent(JList list,
Object value, int index, boolean isSelected,
boolean cellHasFocus) {
return index >= 0 ? new JLabel(
((RequirementStatus) ((ComboBoxModel) status.getModel())
.getElementAt(index)).getStatus())
: new JLabel("-none-");
}
});
我不得不說條件添加到代碼，因爲某種原因而構建GUI代碼請求在位置-1處呈現元素。如果我不返回帶有文本的標籤，則組合框完全不顯示。
編輯：
這是我的錯誤，如果這個解決方法是不存在的：
java.lang.ArrayIndexOutOfBoundsException: -1
at java.util.ArrayList.get(ArrayList.java:324)
at net.sourceforge.javydreamercsw.client.ui.nodes.actions.EditRequirementDialog$5.getElementAt(EditRequirementDialog.java:119)
at net.sourceforge.javydreamercsw.client.ui.nodes.actions.EditRequirementDialog$6.getListCellRendererComponent(EditRequirementDialog.java:127)
at javax.swing.plaf.basic.BasicComboBoxUI.getDisplaySize(BasicComboBoxUI.java:1334)
at javax.swing.plaf.basic.BasicComboBoxUI.getMinimumSize(BasicComboBoxUI.java:903)
at javax.swing.plaf.basic.BasicComboBoxUI.getPreferredSize(BasicComboBoxUI.java:892)
at javax.swing.JComponent.getPreferredSize(JComponent.java:1642)
at javax.swing.GroupLayout$ComponentSpring.calculateNonlinkedPreferredSize(GroupLayout.java:2944)
at javax.swing.GroupLayout$ComponentSpring.calculatePreferredSize(GroupLayout.java:2905)
at javax.swing.GroupLayout$Spring.getPreferredSize(GroupLayout.java:1325)
at javax.swing.GroupLayout$Group.getSpringSize(GroupLayout.java:1604)
at javax.swing.GroupLayout$Group.calculateSize(GroupLayout.java:1593)
at javax.swing.GroupLayout$Group.calculatePreferredSize(GroupLayout.java:1568)
at javax.swing.GroupLayout$Spring.getPreferredSize(GroupLayout.java:1325)
at javax.swing.GroupLayout$Group.getSpringSize(GroupLayout.java:1604)
at javax.swing.GroupLayout$Group.calculateSize(GroupLayout.java:1593)
at javax.swing.GroupLayout$Group.calculatePreferredSize(GroupLayout.java:1568)
at javax.swing.GroupLayout$Spring.getPreferredSize(GroupLayout.java:1325)
at javax.swing.GroupLayout$Group.getSpringSize(GroupLayout.java:1604)
at javax.swing.GroupLayout$Group.calculateSize(GroupLayout.java:1593)
at javax.swing.GroupLayout$Group.calculatePreferredSize(GroupLayout.java:1568)
at javax.swing.GroupLayout$Spring.getPreferredSize(GroupLayout.java:1325)
at javax.swing.GroupLayout$Group.getSpringSize(GroupLayout.java:1604)
at javax.swing.GroupLayout$Group.calculateSize(GroupLayout.java:1590)
at javax.swing.GroupLayout$Group.calculatePreferredSize(GroupLayout.java:1568)
at javax.swing.GroupLayout$Spring.getPreferredSize(GroupLayout.java:1325)
at javax.swing.GroupLayout$Group.getSpringSize(GroupLayout.java:1604)
at javax.swing.GroupLayout$Group.calculateSize(GroupLayout.java:1588)
at javax.swing.GroupLayout$Group.calculatePreferredSize(GroupLayout.java:1568)
at javax.swing.GroupLayout$Spring.getPreferredSize(GroupLayout.java:1325)
at javax.swing.GroupLayout$Group.getSpringSize(GroupLayout.java:1604)
at javax.swing.GroupLayout$Group.calculateSize(GroupLayout.java:1588)
at javax.swing.GroupLayout$Group.calculatePreferredSize(GroupLayout.java:1568)
at javax.swing.GroupLayout$Spring.getPreferredSize(GroupLayout.java:1325)
at javax.swing.GroupLayout$SequentialGroup.setValidSize(GroupLayout.java:1972)
at javax.swing.GroupLayout$Group.setSize(GroupLayout.java:1553)
at javax.swing.GroupLayout.calculateAutopadding(GroupLayout.java:1058)
at javax.swing.GroupLayout.layoutContainer(GroupLayout.java:897)
at java.awt.Container.layout(Container.java:1419)
at java.awt.Container.doLayout(Container.java:1408)
at java.awt.Container.validateTree(Container.java:1505)
at java.awt.Container.validateTree(Container.java:1511)
at java.awt.Container.validateTree(Container.java:1511)
at java.awt.Container.validateTree(Container.java:1511)
at java.awt.Container.validate(Container.java:1478)
at java.awt.Dialog.conditionalShow(Dialog.java:890)
at java.awt.Dialog.show(Dialog.java:1036)
at java.awt.Component.show(Component.java:1591)
at java.awt.Component.setVisible(Component.java:1543)
at java.awt.Window.setVisible(Window.java:843)
at java.awt.Dialog.setVisible(Dialog.java:987)
at net.sourceforge.javydreamercsw.client.ui.nodes.actions.EditRequirementAction$1.run(EditRequirementAction.java:33)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:666)
at java.awt.EventQueue.access$400(EventQueue.java:81)
at java.awt.EventQueue$2.run(EventQueue.java:627)
at java.awt.EventQueue$2.run(EventQueue.java:625)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:636)
at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:159)
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)
[catch] at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
我知道這應該是一件容易的事情，就像一個標誌設置，但我可以」找到它。
任何想法？
解決方案： 取下模型倍率和改變渲染器代碼如下：
status.setRenderer(new ListCellRenderer() {
@Override
public Component getListCellRendererComponent(JList list,
Object value, int index, boolean isSelected,
boolean cellHasFocus) {
return index >= 0 ? new JLabel(
((RequirementStatus) value).getStatus())
: new JLabel(((RequirementStatus) list.getSelectedValue()).getStatus());
}
});
爲了更快得到更好的幫助，請發佈[SSCCE]（http://sscce.org/）。 –
您知道'（（ComboBoxModel）status.getModel（）） .getElementAt（index））'嚴格等於提供的參數'value'嗎？無論如何，如果第一次顯示時，當前選中的對象是'null'，'null'不是你模型的一部分，UI沒有其他選擇，只能提供-1作爲索引 –
爲什麼你重寫模型？我認爲沒有理由這樣做。如果要在模型中存儲自定義對象，則只需提供自定義渲染器即可顯示對象中的數據。 – camickr