我创建了一个包含以下组件的JFrame：JLabel（只是一个简单的文字标签），JComboBox和JButton。初始化后，JFrame从配置文件中读取，配置文件的条目将复制到HashMap。我有一个按钮可以进一步放置＆＃34; local＆＃34; HashMap中的条目（因此配置文件在读取之后不会被触及）。
我的问题是，我添加的每一行的删除按钮在初始化帧时都能正常工作，然后直接删除一些条目。在调用DISPOSE并重新初始化帧之后，delete函数会抛出一些NullPointerException。 frameContainer（我的JFrame）似乎不再找到组件（虽然它们在重新初始化后又被添加了！）
这里有一些代码：
/**
* The standard constructor.
*
* @param extensionModel The model of the ModifyXESHeader view.
*/
public ModifyXESHeaderExtensions(ModifyXESHeaderModel extensionModel) {
super("Modify Header of XES File - Extensions");
this.frameContainer = new JFrame();
this.frameContainer.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
this.frameContainer.setLayout(new GridLayout(0,3));
this.headerModel = extensionModel;
if (this.headerModel.componentExtensionMap.isEmpty()) {
this.count = 0;
} else {
this.count = this.headerModel.componentExtensionMap.size();
}
this.labelName = "label";
this.comboBoxName = "comboBox";
this.deleteButtonName = "deleteButton";
this.comboBoxItems = new String[]{"Concept.concept", "Lifecycle.lifecycle", "Organizational.org", "Time.time", "Semantic.semantic", "ID.identity", "Cost.cost"};
this.comboBoxItemsList = new ArrayList<String>();
addAllItemsToList(this.comboBoxItems);
this.addExtensionButton = new JButton("Add extension");
this.cancelButton = new JButton("Cancel");
this.emptyLabel = new JLabel();
this.frameContainer.add(this.addExtensionButton);
this.frameContainer.add(this.cancelButton);
this.frameContainer.add(this.emptyLabel);
//initialize the frame based upon the entries in the fileconfig.
initializeFrame();
this.frameContainer.revalidate();
this.frameContainer.repaint();
//pack'n'show
this.frameContainer.pack();
this.frameContainer.setLocationRelativeTo(null);
this.frameContainer.setVisible(true);
}
/**
* initializes the frame.
*/
public void initializeFrame() {
//for re-initializing the frame
if (!this.headerModel.componentExtensionMap.isEmpty()) {
for (int i = 1; i <= (this.headerModel.componentExtensionMap.size()); i++) {
if (this.headerModel.componentExtensionMap.get(this.comboBoxName + i) != null) {
this.extensionNamePrefixLabel = (JLabel) this.headerModel.componentExtensionMap.get(this.labelName + i);
this.extensionComboBox = (JComboBox) this.headerModel.componentExtensionMap.get(this.comboBoxName + i);
this.deleteButton = (JButton) this.headerModel.componentExtensionMap.get(this.deleteButtonName + i);
this.frameContainer.add(this.extensionNamePrefixLabel);
this.frameContainer.add(this.extensionComboBox);
this.deleteButton.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
deleteRow(e);
}
});
this.frameContainer.add(this.deleteButton);
this.frameContainer.revalidate();
this.frameContainer.repaint();
this.frameContainer.pack();
}
}
} else {
//Proof whether the config contains extension keys
Iterator<String> iterator = this.headerModel.fileConfig.getKeys();
while (iterator.hasNext()) {
String key = iterator.next();
String props = (String) this.headerModel.fileConfig.getProperty(key);
String[] tempStringArray = null;
if (!props.contains(":")) {
continue;
} else {
tempStringArray = props.split(":");
}
String selectedItem = null;
for (String listItem : this.comboBoxItemsList) {
System.out.println("Item: " + listItem);
if (listItem.contains(tempStringArray[0])) {
System.out.println("true");
selectedItem = listItem;
break;
}
}
if (this.comboBoxItemsList.contains(selectedItem)) {
++this.count;
this.extensionNamePrefixLabel = new JLabel("Extension Name.Prefix");
this.extensionComboBox = new JComboBox(this.comboBoxItems);
this.extensionComboBox.setSelectedItem(selectedItem);
this.deleteButton = new JButton("Delete");
this.deleteButton.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
deleteRow(e);
}
});
this.frameContainer.add(this.extensionNamePrefixLabel);
this.frameContainer.add(this.extensionComboBox);
this.frameContainer.add(this.deleteButton);
this.frameContainer.revalidate();
this.frameContainer.repaint();
this.frameContainer.pack();
this.headerModel.addExtensionComponentToMap(this.labelName, this.extensionNamePrefixLabel, this.count);
this.headerModel.addExtensionComponentToMap(this.comboBoxName, this.extensionComboBox, this.count);
this.headerModel.addExtensionComponentToMap(this.deleteButtonName, this.deleteButton, this.count);
}
}
}
}
在这个函数中，将抛出NullPointer（在frameContainer想要删除第一个组件的地方）：
/**
* Deletes a row of the view.
*
* @param e ActionEvent.
*/
public void deleteRow(ActionEvent e) {
Integer buttonNumber = this.headerModel.indexExtensionMap.get(e.getSource());
JLabel tempLabel = (JLabel) this.headerModel.componentExtensionMap.get(this.labelName + buttonNumber);
JComboBox tempBox = (JComboBox) this.headerModel.componentExtensionMap.get(this.comboBoxName + buttonNumber);
JButton tempButton = (JButton) this.headerModel.componentExtensionMap.get(this.deleteButtonName + buttonNumber);
this.frameContainer.remove(tempLabel);
this.frameContainer.remove(tempBox);
this.frameContainer.remove(tempButton);
this.headerModel.deleteExtensionComponentFromMap(this.labelName + buttonNumber, tempLabel);
this.headerModel.deleteExtensionComponentFromMap(this.comboBoxName + buttonNumber, tempBox);
this.headerModel.deleteExtensionComponentFromMap(this.deleteButtonName + buttonNumber, tempButton);
this.frameContainer.revalidate();
this.frameContainer.repaint();
this.frameContainer.pack();
}
顺便说一句：无论如何，组件都会从GUI中消失。
完全堆积痕迹：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at java.awt.Container.remove(Container.java:1259)
at javax.swing.JFrame.remove(JFrame.java:587)
at UI.ModifyXESHeaderExtensions.deleteRow(ModifyXESHeaderExtensions.java:211)
at UI.Controller.ModifyXESHeaderExtensionsController$1.actionPerformed(ModifyXESHeaderExtensionsController.java:59)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2346)
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:6525)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6290)
at java.awt.Container.processEvent(Container.java:2234)
at java.awt.Component.dispatchEventImpl(Component.java:4881)
at java.awt.Container.dispatchEventImpl(Container.java:2292)
at java.awt.Component.dispatchEvent(Component.java:4703)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4533)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
at java.awt.Container.dispatchEventImpl(Container.java:2278)
at java.awt.Window.dispatchEventImpl(Window.java:2739)
at java.awt.Component.dispatchEvent(Component.java:4703)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:746)
at java.awt.EventQueue.access$400(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:697)
at java.awt.EventQueue$3.run(EventQueue.java:691)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:719)
at java.awt.EventQueue$4.run(EventQueue.java:717)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:716)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)`