我有一个对话框，其中jtree中的每个条目都有其在不同面板中的相应选项，在选择变化时会更新。如果其中一个条目的选项设置为无效状态，当用户尝试更改为树中的不同条目时，我希望出现一个错误对话框并且不更改选择。
我尝试在 JTree 上使用 valueChangeListener 来执行此操作，但目前如果出现错误，则必须让 valueChanged 方法对旧选择调用“setSelectionRow”。为了避免 StackOverflow，我在执行此操作之前将布尔值“isError”设置为 true，以便忽略新的 valueChanged 事件。不知何故，我有直觉认为这不是最好的解决方案。 ;-)
我该怎么做呢？对于这种情况，有没有好的设计模式？
【问题讨论】：
标签： java swing design-patterns error-handling
我没有找到更好的方法，但这种方法对我来说很好用。 我知道在 Delphi 中这是一个非常方便的事件：“在更改选择之前”，您可以非常轻松地停止更改选择。
这是我的防止无限递归问题的java代码
navTree.addTreeSelectionListener(new TreeSelectionListener() {
boolean treeSelectionListenerEnabled = true;
public void valueChanged(TreeSelectionEvent e) {
if (treeSelectionListenerEnabled) {
if (ok to change selection...) {
...
} else {
TreePath treePath = e.getOldLeadSelectionPath();
treeSelectionListenerEnabled = false;
try {
// prevent from leaving the last visited node
navTree.setSelectionPath(treePath);
} finally {
treeSelectionListenerEnabled = true;
}
}
}
}
});
始终记得删除您添加的所有侦听器，以防止内存泄漏。
这是另一种方法：
private class VetoableTreeSelectionModel extends DefaultTreeSelectionModel {
public void setSelectionPath(TreePath path){
if (allow selection change?) {
super.setSelectionPath(path);
}
}
}
{
navTree.setSelectionModel(new VetoableTreeSelectionModel());
}
【讨论】：
不确定这是最佳实践，但也许您可以在要验证的组件上放置一个 FocusListener...在调用事件时调用您的验证，然后如果您不想要焦点，则使用该事件因为验证失败而被移动？
稍后编辑：
至少对于 java 8（我没有检查早期版本），这个解决方案不起作用，因为 FocusEvent 似乎不是一个低级事件。因此不能食用。参见方法 AWTEvent.consume()
【讨论】：
这是我的解决方案。
在 JTree 子类中：
protected void processMouseEvent(MouseEvent e) {
TreePath selPath = getPathForLocation(e.getX(), e.getY());
try {
fireVetoableChange(LEAD_SELECTION_PATH_PROPERTY, getLeadSelectionPath(), selPath);
}
catch (PropertyVetoException ex) {
// OK, we do not want change to happen
return;
}
super.processMouseEvent(e);
}
然后在树中使用类：
VetoableChangeListener vcl = new VetoableChangeListener() {
public void vetoableChange(PropertyChangeEvent evt) throws PropertyVetoException {
if ( evt.getPropertyName().equals(JTree.LEAD_SELECTION_PATH_PROPERTY) ) {
try {
<some code logic that has to be satisfied>
} catch (InvalidInputException e) {
throw new PropertyVetoException("", evt);
}
}
}
};
tree.addVetoableChangeListener(vcl);
该机制在尽可能早的地方开始。鼠标动作被截获，将要选择的路径通告给 VetoableChangeListeners。在具体的 VCL 中，检查更改属性，如果是前导选择，则检查否决逻辑。如果需要否决，VCL 会抛出 PropertyVetoException，否则鼠标事件处理将照常进行并进行选择。 简而言之，这使得潜在客户选择属性成为约束属性。
【讨论】：
设置一个实现适当语义的 TreeSelectionModel。
【讨论】：
下面是一个实现 TreeSelectionModel 的示例，它包装了另一个 TreeSelectionModel 但允许否决选择：
public class VetoableTreeSelectionModel implements TreeSelectionModel
{
private final ListenerList<VetoableTreeSelectionListener> m_vetoableTreeSelectionListeners = new ListenerList<VetoableTreeSelectionListener>();
private final DefaultTreeSelectionModel m_treeSelectionModel = new DefaultTreeSelectionModel();
/**
* {@inheritDoc}
*/
public void addTreeSelectionListener(final TreeSelectionListener listener)
{
m_treeSelectionModel.addTreeSelectionListener(listener);
}
/**
* {@inheritDoc}
*/
public void removeTreeSelectionListener(final TreeSelectionListener listener)
{
m_treeSelectionModel.removeTreeSelectionListener(listener);
}
/**
* Add a vetoable tree selection listener
*
* @param listener the listener
*/
public void addVetoableTreeSelectionListener(final VetoableTreeSelectionListener listener)
{
m_vetoableTreeSelectionListeners.addListener(listener);
}
/**
* Remove a vetoable tree selection listener
*
* @param listener the listener
*/
public void removeVetoableTreeSelectionListener(final VetoableTreeSelectionListener listener)
{
m_vetoableTreeSelectionListeners.removeListener(listener);
}
/**
* {@inheritDoc}
*/
public void addPropertyChangeListener(final PropertyChangeListener listener)
{
m_treeSelectionModel.addPropertyChangeListener(listener);
}
/**
* {@inheritDoc}
*/
public void removePropertyChangeListener(final PropertyChangeListener listener)
{
m_treeSelectionModel.removePropertyChangeListener(listener);
}
/**
* {@inheritDoc}
*/
public void addSelectionPath(final TreePath path)
{
try
{
m_vetoableTreeSelectionListeners.fireVetoableEvent(new VetoableAction<VetoableTreeSelectionListener>() {
public void fireEvent(final VetoableTreeSelectionListener listener) throws EventVetoedException
{
listener.aboutToAddSelectionPath(path);
}});
m_treeSelectionModel.addSelectionPath(path);
}
catch (final EventVetoedException e)
{
return;
}
}
/**
* {@inheritDoc}
*/
public void addSelectionPaths(final TreePath[] paths)
{
try
{
m_vetoableTreeSelectionListeners.fireVetoableEvent(new VetoableAction<VetoableTreeSelectionListener>() {
public void fireEvent(final VetoableTreeSelectionListener listener) throws EventVetoedException
{
listener.aboutToAddSelectionPaths(paths);
}});
m_treeSelectionModel.addSelectionPaths(paths);
}
catch (final EventVetoedException e)
{
return;
}
}
/**
* {@inheritDoc}
*/
public void clearSelection()
{
try
{
m_vetoableTreeSelectionListeners.fireVetoableEvent(new VetoableAction<VetoableTreeSelectionListener>() {
public void fireEvent(final VetoableTreeSelectionListener listener) throws EventVetoedException
{
listener.aboutToClearSelection();
}});
m_treeSelectionModel.clearSelection();
}
catch (final EventVetoedException e)
{
return;
}
}
/**
* {@inheritDoc}
*/
public TreePath getLeadSelectionPath()
{
return m_treeSelectionModel.getLeadSelectionPath();
}
/**
* {@inheritDoc}
*/
public int getLeadSelectionRow()
{
return m_treeSelectionModel.getLeadSelectionRow();
}
/**
* {@inheritDoc}
*/
public int getMaxSelectionRow()
{
return m_treeSelectionModel.getMaxSelectionRow();
}
/**
* {@inheritDoc}
*/
public int getMinSelectionRow()
{
return m_treeSelectionModel.getMinSelectionRow();
}
/**
* {@inheritDoc}
*/
public RowMapper getRowMapper()
{
return m_treeSelectionModel.getRowMapper();
}
/**
* {@inheritDoc}
*/
public int getSelectionCount()
{
return m_treeSelectionModel.getSelectionCount();
}
public int getSelectionMode()
{
return m_treeSelectionModel.getSelectionMode();
}
/**
* {@inheritDoc}
*/
public TreePath getSelectionPath()
{
return m_treeSelectionModel.getSelectionPath();
}
/**
* {@inheritDoc}
*/
public TreePath[] getSelectionPaths()
{
return m_treeSelectionModel.getSelectionPaths();
}
/**
* {@inheritDoc}
*/
public int[] getSelectionRows()
{
return m_treeSelectionModel.getSelectionRows();
}
/**
* {@inheritDoc}
*/
public boolean isPathSelected(final TreePath path)
{
return m_treeSelectionModel.isPathSelected(path);
}
/**
* {@inheritDoc}
*/
public boolean isRowSelected(final int row)
{
return m_treeSelectionModel.isRowSelected(row);
}
/**
* {@inheritDoc}
*/
public boolean isSelectionEmpty()
{
return m_treeSelectionModel.isSelectionEmpty();
}
/**
* {@inheritDoc}
*/
public void removeSelectionPath(final TreePath path)
{
try
{
m_vetoableTreeSelectionListeners.fireVetoableEvent(new VetoableAction<VetoableTreeSelectionListener>() {
public void fireEvent(final VetoableTreeSelectionListener listener) throws EventVetoedException
{
listener.aboutRemoveSelectionPath(path);
}});
m_treeSelectionModel.removeSelectionPath(path);
}
catch (final EventVetoedException e)
{
return;
}
}
/**
* {@inheritDoc}
*/
public void removeSelectionPaths(final TreePath[] paths)
{
try
{
m_vetoableTreeSelectionListeners.fireVetoableEvent(new VetoableAction<VetoableTreeSelectionListener>() {
public void fireEvent(final VetoableTreeSelectionListener listener) throws EventVetoedException
{
listener.aboutRemoveSelectionPaths(paths);
}});
m_treeSelectionModel.removeSelectionPaths(paths);
}
catch (final EventVetoedException e)
{
return;
}
}
/**
* {@inheritDoc}
*/
public void resetRowSelection()
{
try
{
m_vetoableTreeSelectionListeners.fireVetoableEvent(new VetoableAction<VetoableTreeSelectionListener>() {
public void fireEvent(final VetoableTreeSelectionListener listener) throws EventVetoedException
{
listener.aboutToResetRowSelection();
}});
m_treeSelectionModel.resetRowSelection();
}
catch (final EventVetoedException e)
{
return;
}
}
/**
* {@inheritDoc}
*/
public void setRowMapper(final RowMapper newMapper)
{
m_treeSelectionModel.setRowMapper(newMapper);
}
/**
* {@inheritDoc}
*/
public void setSelectionMode(final int mode)
{
try
{
m_vetoableTreeSelectionListeners.fireVetoableEvent(new VetoableAction<VetoableTreeSelectionListener>() {
public void fireEvent(final VetoableTreeSelectionListener listener) throws EventVetoedException
{
listener.aboutToSetSelectionMode(mode);
}});
m_treeSelectionModel.setSelectionMode(mode);
}
catch (final EventVetoedException e)
{
return;
}
}
/**
* {@inheritDoc}
*/
public void setSelectionPath(final TreePath path)
{
try
{
m_vetoableTreeSelectionListeners.fireVetoableEvent(new VetoableAction<VetoableTreeSelectionListener>() {
public void fireEvent(final VetoableTreeSelectionListener listener) throws EventVetoedException
{
listener.aboutToSetSelectionPath(path);
}});
m_treeSelectionModel.setSelectionPath(path);
}
catch (final EventVetoedException e)
{
return;
}
}
/**
* {@inheritDoc}
*/
public void setSelectionPaths(final TreePath[] paths)
{
try
{
m_vetoableTreeSelectionListeners.fireVetoableEvent(new VetoableAction<VetoableTreeSelectionListener>() {
public void fireEvent(final VetoableTreeSelectionListener listener) throws EventVetoedException
{
listener.aboutToSetSelectionPaths(paths);
}});
m_treeSelectionModel.setSelectionPaths(paths);
}
catch (final EventVetoedException e)
{
return;
}
}
/**
* {@inheritDoc}
*/
@Override
public String toString()
{
return m_treeSelectionModel.toString();
}
}
下面是听者：
public interface VetoableTreeSelectionListener
{
/**
* About to add a path to the selection
*
* @param path the path to add
*
* @throws EventVetoedException
*/
void aboutToAddSelectionPath(TreePath path) throws EventVetoedException;
/**
* About to add paths to the selection
*
* @param paths the paths to add
*
* @throws EventVetoedException
*/
void aboutToAddSelectionPaths(TreePath[] paths) throws EventVetoedException;
/**
* About to clear selection
*
* @throws EventVetoedException
*/
void aboutToClearSelection() throws EventVetoedException;
/**
* About to remove a selection path
*
* @param path the path
*
* @throws EventVetoedException
*/
void aboutRemoveSelectionPath(TreePath path) throws EventVetoedException;
/**
* About to remove multiple selection paths
*
* @param paths the paths
*
* @throws EventVetoedException
*/
void aboutRemoveSelectionPaths(TreePath[] paths) throws EventVetoedException;
/**
* About to reset the row selection
*
* @throws EventVetoedException
*/
void aboutToResetRowSelection() throws EventVetoedException;
/**
* About to set the selection mode
*
* @param mode the selection mode
*
* @throws EventVetoedException
*/
void aboutToSetSelectionMode(int mode) throws EventVetoedException;
/**
* About to set the selection path
*
* @param path the path
*
* @throws EventVetoedException
*/
void aboutToSetSelectionPath(TreePath path) throws EventVetoedException;
/**
* About to set the selection paths
*
* @param paths the paths
*
* @throws EventVetoedException
*/
void aboutToSetSelectionPaths(TreePath[] paths) throws EventVetoedException;
}
您可以使用自己的 ListenerList 实现，但您明白了……
【讨论】：
为了防止选择，我只是继承了 DefaultTreeSelectionModel 并覆盖了所有方法来检查我不想被选择的对象（下面我的示例中的“DisplayRepoOwner”实例）。如果对象可以被选中，我调用 super 方法；否则我没有。我将 JTree 的选择模型设置为该子类的一个实例。
public class MainTreeSelectionModel extends DefaultTreeSelectionModel {
public void addSelectionPath(TreePath path) {
if (path.getLastPathComponent() instanceof DisplayRepoOwner) {
return;
}
super.addSelectionPath(path);
}
public void addSelectionPaths(TreePath[] paths) {
for (TreePath tp : paths) {
if (tp.getLastPathComponent() instanceof DisplayRepoOwner) {
return;
}
}
super.addSelectionPaths(paths);
}
public void setSelectionPath(TreePath path) {
if (path.getLastPathComponent() instanceof DisplayRepoOwner) {
return;
}
super.setSelectionPath(path);
}
public void setSelectionPaths(TreePath[] paths) {
for (TreePath tp : paths) {
if (tp.getLastPathComponent() instanceof DisplayRepoOwner) {
return;
}
}
super.setSelectionPaths(paths);
}
}
【讨论】：
在调查同一问题的解决方案时偶然发现了此线程。首先，让我告诉你一些没有用的事情。我试图用树注册 MouseListeners 和所有这些。问题是 TreeUI 的鼠标侦听器在我的 JTree 之前就开始处理事件，这意味着设置标志或类似的东西为时已晚。除此之外，这个解决方案产生了一些丑陋的代码，我通常会避免它。
现在是实际解决方案！
在使用几个 Thread.dumpStack() 调用来获取堆栈转储后，我找到了我想要覆盖的方法。我扩展了 BasicTreeUI 并覆盖了“受保护的 void selectPathForEvent（TreePath 路径，MouseEvent 事件）”。
这将使您能够在选择实际发生之前访问导致选择的鼠标事件。然后，您可以使用 event.consume() 所需的任何逻辑，如果要停止选择则返回，执行所需的任何选择或通过调用 super.selectPathForEvent(path, event); 将其传递给默认处理；
只需记住设置您在 JTree 中创建的 UI。这个错误浪费了我生命中的几分钟;-)
【讨论】：