问题描述

我目前正在编写一个用于手动将数据从一张纸复制到数据库的应用程序。这个应用程序有很多小部件，用户可以在其中输入数据。为了使 UI 保持整洁，我决定使用选项卡式 Pane ，将输入字段分隔成逻辑单元。

该应用程序最重要的特性是它应该可以单独通过键盘使用。所以你应该能够通过击键来切换标签。默认情况下，这可以使用 CTRL+PgUp/PgDown。但是，作为额外的便利，我想在用户将焦点从当前选项卡上的最后一个小部件移出时立即激活下一个选项卡。

因此，如果用户将焦点放在最后一个文本字段上，然后按下选项卡，我想激活下一个选项卡，并将焦点放在其中的第一个小部件上。

为了解决这个问题，我将 jTabbedPane 标记为 focusCycleRootProvider 并添加了自定义 FocusTraversalPolicy。我当前的问题是:一旦我以编程方式激活下一个选项卡(使用 setSelectedIndex)，这发生在 getComponentAfter 方法中，方法 getComponentAfter 第二次执行。这违背了我目前的逻辑。我似乎无法找到一种方法来防止这种情况发生。有什么想法吗？

在下面的示例中，您将看到一个 ArrayIndexOutOfBoundsException。发生这种情况是因为 getComponentAfter 被调用了两次。一次在第一个选项卡上，一次在第二个选项卡上。但是两次使用相同的组件作为参数。这意味着，第二次，for 循环将找不到匹配的组件，因此计数器 i 将与第二个选项卡中的组件 一样大+ 1. 这会导致异常。

测试可执行文件

/*
 * TestFrame.java
 *
 * Created on Apr 18, 2011, 4:37:52 PM
 */

package testrun;

import java.awt.Component;
import java.awt.event.FocusAdapter;
import java.awt.event.FocusEvent;

/**
 *
 * @author malbert
 */
public class TestFrame extends javax.swing.JFrame {

    /** Creates new form TestFrame */
    public TestFrame() {
        initComponents();
        jTabbedPane1.setFocusTraversalPolicyProvider(true);
        jTabbedPane1.setFocusTraversalPolicy(new EasyTabberFocusTraversalPolicy(jTabbedPane1));

        jTabbedPane1.addFocusListener(new FocusAdapter() {

            @Override
            public void focusGained(FocusEvent e) {
                super.focusGained(e);
                jTabbedPane1.setSelectedIndex(0);
                Component ca = jTabbedPane1.getFocusTraversalPolicy().getFirstComponent(jTabbedPane1);
                if (ca != null) {
                    ca.requestFocusInWindow();
                }
            }
        });
    }

    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">//GEN-BEGIN:initComponents
    private void initComponents() {

        jTabbedPane1 = new javax.swing.JTabbedPane();
        jPanel1 = new javax.swing.JPanel();
        jTextField2 = new javax.swing.JTextField();
        jTextField3 = new javax.swing.JTextField();
        jPanel2 = new javax.swing.JPanel();
        jButton1 = new javax.swing.JButton();
        jButton2 = new javax.swing.JButton();
        jTextField4 = new javax.swing.JTextField();
        jTextField1 = new javax.swing.JTextField();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jTextField2.setText("jTextField2");

        jTextField3.setText("jTextField3");

        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(jTextField2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addComponent(jTextField3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addContainerGap(289, Short.MAX_VALUE))
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jTextField2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(jTextField3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(168, Short.MAX_VALUE))
        );

        jTabbedPane1.addTab("tab1", jPanel1);

        jButton1.setText("jButton1");

        jButton2.setText("jButton2");

        jTextField4.setText("jTextField4");

        javax.swing.GroupLayout jPanel2Layout = new javax.swing.GroupLayout(jPanel2);
        jPanel2.setLayout(jPanel2Layout);
        jPanel2Layout.setHorizontalGroup(
            jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel2Layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(jPanel2Layout.createSequentialGroup()
                        .addComponent(jButton1)
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                        .addComponent(jButton2))
                    .addComponent(jTextField4, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addContainerGap(165, Short.MAX_VALUE))
        );
        jPanel2Layout.setVerticalGroup(
            jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel2Layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jButton1)
                    .addComponent(jButton2))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(jTextField4, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(162, Short.MAX_VALUE))
        );

        jTabbedPane1.addTab("tab2", jPanel2);

        jTextField1.setText("jTextField1");

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(jTabbedPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 376, Short.MAX_VALUE)
                    .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(jTabbedPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 251, Short.MAX_VALUE)
                .addContainerGap())
        );

        pack();
    }// </editor-fold>//GEN-END:initComponents

    /**
    * @param args the command line arguments
    */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new TestFrame().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify//GEN-BEGIN:variables
    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton2;
    private javax.swing.JPanel jPanel1;
    private javax.swing.JPanel jPanel2;
    private javax.swing.JTabbedPane jTabbedPane1;
    private javax.swing.JTextField jTextField1;
    private javax.swing.JTextField jTextField2;
    private javax.swing.JTextField jTextField3;
    private javax.swing.JTextField jTextField4;
    // End of variables declaration//GEN-END:variables

}

遍历策略

package testrun;

import java.awt.Component;
import java.awt.Container;
import javax.swing.JTabbedPane;
import javax.swing.LayoutFocusTraversalPolicy;

/**
 *
 * @author malbert
 */
public class EasyTabberFocusTraversalPolicy extends LayoutFocusTraversalPolicy {

    private final JTabbedPane container;
    private int currentTab = 0;

    public EasyTabberFocusTraversalPolicy(JTabbedPane container) {
        this.container = container;
    }

    @Override
    public Component getComponentAfter(Container aContainer, Component aComponent) {
        System.out.println("after " + aComponent);
        Component comp = container.getComponentAt(currentTab);
        if (Container.class.isInstance(comp)) {
            Component[] components = ((Container) comp).getComponents();
            int i = 0;
            for (i = 0; i < components.length; i++) {
                if (!components[i].isEnabled() || !components[i].isFocusable()) {
                    continue;
                }
                if (components[i].equals(aComponent)) {
                    break;
                }
            }
            if (i == components.length - 1) {
                // we reached the end. Go to the next tab!
                currentTab = currentTab + 1;
                Component fc = firstComponentInCurrentTab();
                activateTab(currentTab);
                return fc;
            } else {
                return components[i + 1];
            }
        } else {
            return comp;
        }
    }

    @Override
    public Component getComponentBefore(Container aContainer, Component aComponent) {
        System.out.println("before");
        return super.getComponentBefore(aContainer, aComponent);
    }

    @Override
    public Component getFirstComponent(Container aContainer) {
        System.out.println("first");
        return firstComponentInCurrentTab();
    }

    @Override
    public Component getLastComponent(Container aContainer) {
        System.out.println("last");
        return lastComponentInCurrentTab();
    }

    private Component firstComponentInCurrentTab() {
        Component comp = container.getComponentAt(currentTab);
        if (comp instanceof Container) {
            Component[] components = ((Container) comp).getComponents();
            if (components.length == 0) {
                return null;
            }
            return components[0];
        } else {
            return comp;
        }
    }

    private Component lastComponentInCurrentTab() {
        Component comp = container.getComponentAt(currentTab);
        if (comp instanceof Container) {
            Component[] components = ((Container) comp).getComponents();
            if (components.length == 0) {
                return null;
            }
            return components[components.length - 1];
        } else {
            return comp;
        }
    }

    private void activateTab(int index) {
        // wrap around
        if (index < 0) {
            index = container.getTabCount() - 1;
        } else if (index > container.getTabCount() - 1) {
            index = 0;
        }
        currentTab = index;
        container.setSelectedIndex(index);
    }
}

最佳答案

FTP 是......真正令人痛苦的痛苦;-)

不完全确定到底是什么导致了 NPE，只是简化了您的代码(如果您有访问最后一个的方法，最好使用它):

@Override
public Component getComponentAfter(Container aContainer, Component aComponent) {
    System.out.println("after " + aComponent);
    Component last = lastComponentInCurrentTab();
    if (aComponent == last) {
      // we reached the end. Go to the next tab!
      currentTab = currentTab + 1;
      Component fc = firstComponentInCurrentTab();
      activateTab(currentTab);
      return fc;

    }
    return super.getComponentAfter(aContainer, aComponent);
}

AIOOB 消失了，显示了第二个选项卡……但没有聚焦。发生这种情况的原因是(只是猜测，因为我在其他设置中看到过类似的东西，没有记住所有肮脏的细节；)在返回时第二个选项卡的第一个组件还没有资格接收焦点，所以它进一步转移到选项卡外的文本。

编辑:必须修改我的猜测 - 经过一些挖掘，问题似乎是对 getFirst/LastComponent 的错误覆盖。他们必须返回所有选项卡的第一个/最后一个，即第一个始终是第一个选项卡的第一个，最后一个始终是最后一个选项卡的最后一个。这是第一个片段:

@Override
public Component getFirstComponent(Container aContainer) {
    System.out.println("first");
    return firstComponentInTab(0) ;//firstComponentInCurrentTab();
}

private Component firstComponentInCurrentTab() {
    int tabIndex = currentTab;
    return firstComponentInTab(tabIndex);
}

private Component firstComponentInTab(int tabIndex) {
    Component comp = container.getComponentAt(tabIndex);
    LOG.info("comp: " + comp.getName());
    if (comp instanceof Container) {
        Component[] components = ((Container) comp).getComponents();
        if (components.length == 0) {
            return null;
        }
        return components[0];
    } else {
        return comp;
    }
}

然后向前的标签看起来很好。最后需要类似的，清理留给 OP :-)

顺便说一句:好主意!

Edit2:当心 - 清理不会是微不足道的。 FTP 必须处理其子项的完整层次结构，因此仅检查直接子项很快就会中断(例如对于 JComboBox 等复合组件)

关于java - jTabbedPane 将焦点转移到下一张纸，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/5704512/