当我在JPanel中有一个JTextField并且它有焦点时，按“tab”不会做任何事情......但是按下“shift-tab”会导致焦点丢失（FocusEvent.getOppositeComponent（）为null）。
如果JPanel上有其他可聚焦组件（或者更确切地说是在“焦点循环根”下），则不会发生这种情况：相反，它们会将焦点放在shift-tab上。
在下面的SSCCE中，我演示了这一点......每次在搜索框中按Return键都会向JTable添加一行，这会使其变为可聚焦。您还可以取消注释使JRadioButtons无法对焦的行。
我还看了一下InputMaps，看看shift-tab是否以某种方式参与其中......根本不是。
我也尝试过使用FocusTraversalPolicy来看看我是否能理解这个问题。没有快乐。
我的目标：当焦点循环根目录中有一个可聚焦组件时，停止“shift-tab”导致焦点丢失（焦点消失）。
后
解决方法是添加行
if( oppComp == null ){ impl.searchBox.requestFocus(); }
在搜索框的FocusListener的focusLost方法的末尾...但对我来说这只是一种解决方法... 1）它不能通过理解焦点遍历机制来解决问题; 2）当你需要从搜索框中丢失焦点时，可能会有一些情况......
import java.awt.*;
import java.awt.event.*;
import java.lang.*;
import java.lang.reflect.InvocationTargetException;
import java.util.*;
import javax.swing.*;
import javax.swing.table.*;
class BackTabProb {
JFrame mainFrame;
JTextField searchBox;
JTable resultsTable;
public static void print(String msg) {
System.out.println(msg);
}
public static void main(String[] a_args) throws InvocationTargetException, InterruptedException {
final BackTabProb impl = new BackTabProb();
class Show implements Runnable {
public void run() {
impl.mainFrame = new JFrame("Back Tab problem");
impl.mainFrame.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent windowEvent) {
impl.mainFrame.dispose();
}
});
impl.resultsTable = new JTable();
impl.resultsTable.setFocusable(false);
Vector<Object> dataVector = new Vector<Object>();
Vector<Object> colIdentifiers = new Vector<Object>(Arrays.asList(new String[] { "ONE", "TWO" }));
((DefaultTableModel) impl.resultsTable.getModel()).setDataVector(dataVector, colIdentifiers);
JScrollPane jsp = new JScrollPane(impl.resultsTable);
JPanel northPanel = new JPanel();
northPanel.setLayout(new BoxLayout(northPanel, BoxLayout.X_AXIS));
impl.searchBox = new JTextField("Enter search text", 10);
JLabel label = new JLabel("Search:");
label.setLabelFor(impl.searchBox);
northPanel.add(label);
northPanel.add(impl.searchBox);
ButtonGroup buttonGroup = new ButtonGroup();
ArrayList<JRadioButton> indexButtons = new ArrayList<JRadioButton>();
for (int i = 0; i < 2; i++) {
JRadioButton indexButton = new JRadioButton(i == 0 ? "Stemmer" : "Simple");
// commenting this out means back-tabbing from search box does not result
// in focus going "nowhere"
indexButton.setFocusable(false);
buttonGroup.add(indexButton);
northPanel.add(indexButton);
}
impl.mainFrame.getContentPane().setLayout(new BorderLayout());
impl.mainFrame.getContentPane().add(northPanel, BorderLayout.NORTH);
impl.mainFrame.getContentPane().add(jsp, BorderLayout.CENTER);
impl.mainFrame.pack();
impl.mainFrame.setVisible(true);
print("=== visible");
}
}
EventQueue.invokeAndWait(new Show());
class AddMore implements Runnable {
public void run() {
impl.mainFrame.setFocusTraversalPolicyProvider(true);
class SearchBoxFocusListener implements FocusListener {
public void focusGained(FocusEvent focusEvent) {
print("=== search box got focus");
impl.searchBox.selectAll();
}
public void focusLost(FocusEvent focusEvent) {
Component oppComp = focusEvent.getOppositeComponent();
print(String.format("=== search box lost focus to %s",
oppComp == null ? "nowhere" : oppComp.getClass()));
}
}
impl.searchBox.addFocusListener(new SearchBoxFocusListener());
class SearchBoxActionListener implements ActionListener {
public void actionPerformed( ActionEvent actionEvent ){
if( actionEvent.getSource() != null ){
((DefaultTableModel)impl.resultsTable.getModel()).insertRow( 0, new Object[]{ "blip", "blap" });
// as soon as the table has at least one row it is set to "focusable"
// commenting this out means back-tabbing from search box results
// in focus going "nowhere"
impl.resultsTable.setFocusable( true );
}
}
}
impl.searchBox.addActionListener( new SearchBoxActionListener() );
ActionMap am = impl.searchBox.getActionMap();
print("=== ActionMap");
for (Object key : am.allKeys()) {
print(String.format(" === action key %s", key));
}
for (int i = 0; i < 3; i++) {
print(String.format("=== InputMap type %d", i));
InputMap im = impl.searchBox.getInputMap(i);
KeyStroke[] allKeys = im.allKeys();
if (allKeys != null) {
for (KeyStroke ks : allKeys) {
print(String.format(" === keystroke %s object %s", ks, im.get(ks)));
}
}
}
// various experiments with FocusTraversalPolicy... NB LayoutTraversalPolicy
// is what the framework uses here by default
class MainFrameFocusTraversalPolicy extends LayoutTraversalPolicy {
public Component getComponentAfter(Container arg0, Component arg1) {
Component comp = super.getComponentAfter(arg0, arg1);
print(String.format("=== comp after %s", comp == null ? "Null" : comp.getClass()));
return comp;
}
public Component getComponentBefore(Container arg0, Component arg1) {
Component comp = super.getComponentBefore(arg0, arg1);
print(String.format("=== comp before %s", comp == null ? "Null" : comp.getClass()));
return comp;
}
public Component getDefaultComponent(Container arg0) {
Component comp = super.getDefaultComponent(arg0);
print(String.format("=== default comp %s", comp == null ? "Null" : comp.getClass()));
return comp;
}
public Component getFirstComponent(Container arg0) {
Component comp = super.getFirstComponent(arg0);
print(String.format("=== first comp %s", comp == null ? "Null" : comp.getClass()));
return comp;
// return impl.searchBox;
}
public Component getLastComponent(Container arg0) {
Component comp = super.getLastComponent(arg0);
print(String.format("=== last comp %s", comp == null ? "Null" : comp.getClass()));
return comp;
}
protected boolean accept(Component comp) {
boolean accept = super.accept(comp);
print(String.format("=== accept %s? %s", comp == null ? "Null" : comp.getClass(), accept));
return accept;
}
}
impl.mainFrame.setFocusTraversalPolicy(new MainFrameFocusTraversalPolicy());
}
}
EventQueue.invokeAndWait(new AddMore());
}
}
答案 0 :(得分：3)
也许您可以使用Container#setFocusTraversalKeys(...)方法：
Set<AWTKeyStroke> backwardKeys = Collections.emptySet();
//alone JTextField(pointed out by @mKorbel): impl.mainFrame.setFocusTraversalKeys(
impl.searchBox.setFocusTraversalKeys(
KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS, backwardKeys);
答案 1 :(得分：0)
这仍然属于我的解决方案...但它比我在＃34;后来＆＃34;
下提供的解决方案更有用。if( oppComp == null ){
final Component srcComp = (Component)focusEvent.getSource();
FocusTraversalPolicy ftp = impl.mainFrame.getFocusTraversalPolicy();
Component lastComp = ftp.getLastComponent( impl.mainFrame );
Component beforeComp = ftp.getComponentBefore( impl.mainFrame, srcComp );
if( lastComp == beforeComp ){
EventQueue.invokeLater( new Runnable(){
public void run() {
if( impl.mainFrame.isFocused()){
srcComp.requestFocus();
};
}});
}
}
实际上，这是单个可聚焦组件所面临的情况：在Shift-Tab上，焦点遍历策略然后发现＆＃34;之前＆＃34; comp与＆＃34; last＆＃34;相同可比。在这些圈子下，焦点（与窗口焦点相对）似乎消失了。奇怪的是，在Tab上（横向前进），当＆＃34;之后＆＃34; comp与＆＃34; first＆＃34;相同comp，它没有。这是一个错误吗？
无论如何，确定了这一点后，你必须异步检查窗口的焦点......这样才能让焦点转到另一个窗口。在Shift-Tab上略微闪烁（嘘！）。