监听用户的 JTabbedPane 选项卡选择

Question

如何监听用户对

JTabbedPane

选项卡的选择？

目前，我们附加了

ChangeListener

，但问题是即使用户没有选择选项卡，

ChangeEvent

也会发布。具体来说，它是在删除选项卡并重新计算选项卡索引时发布的。当发生这种情况时，我们不想执行我们应该对用户选择执行的相同逻辑。我不想讨论细节（它们只会让你感到困惑），但这会导致我们的应用程序出现一个讨厌的错误，这不仅仅是性能问题

为了证明这一点，让我向您展示

javax.swing.JTabbedPane#removeTabAt

方法的片段

// triggers ChangeEvent
        if (selected > index) {
            setSelectedIndexImpl(selected - 1, false);

选项卡式窗格中的选项卡应该是动态的。删除和添加回来遵循我们应用程序的要求

这是 MRE：

import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTabbedPane;
import javax.swing.WindowConstants;
import javax.swing.event.ChangeListener;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;

public class TabbedPaneDemo {
    private static JTabbedPane tabbedPane;
    private static JButton removeGreenTabButton;
    private static JButton restoreGreenTabButton;

    public static void main(String[] args) {
        Container mainPanel = createMainPanel();
        JFrame frame = new JFrame("Tabbed Pane demo");
        frame.setContentPane(mainPanel);
        frame.setLocationRelativeTo(null);
        frame.pack();
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

    private static JComponent createMainPanel() {
        JPanel panel = new JPanel(new BorderLayout());
        panel.add(createButtonPanel(), BorderLayout.NORTH);
        panel.add(createTabbedPane());
        return panel;
    }

    private static JPanel createButtonPanel() {
        JPanel panel = new JPanel();
        panel.add(createRemoveTabButton());
        panel.add(createRestoreTabButton());
        return panel;
    }

    private static JButton createRemoveTabButton() {
        removeGreenTabButton = new JButton("Remove green tab");
        removeGreenTabButton.addActionListener(e -> {
            tabbedPane.remove(0);
            restoreGreenTabButton.setEnabled(true);
            removeGreenTabButton.setEnabled(false);
        });
        return removeGreenTabButton;
    }

    private static JButton createRestoreTabButton() {
        restoreGreenTabButton = new JButton("Restore green tab");
        restoreGreenTabButton.setEnabled(false);
        restoreGreenTabButton.addActionListener(e -> {
            tabbedPane.insertTab("Green tab", null, createGreenPanel(), null, 0);
            removeGreenTabButton.setEnabled(true);
            restoreGreenTabButton.setEnabled(false);
        });
        return restoreGreenTabButton;
    }

    private static JTabbedPane createTabbedPane() {
        tabbedPane = new JTabbedPane();
        tabbedPane.addTab("Green tab", createGreenPanel());
        tabbedPane.addTab("Red tab", createRedPanel());
        tabbedPane.setPreferredSize(new Dimension(250, 150));
        tabbedPane.addChangeListener(createChangeListener());
        return tabbedPane;
    }

    private static Component createGreenPanel() {
        JPanel panel = new JPanel();
        panel.setBackground(Color.GREEN);
        return panel;
    }

    private static Component createRedPanel() {
        JPanel panel = new JPanel();
        panel.setBackground(Color.RED);
        return panel;
    }

    private static ChangeListener createChangeListener() {
        // this is supposed to happen only on user tab selections
        return e -> System.out.println("Handling user tab selection...");
    }
}

Java 8

Answer 1

每当发生任何

更改时都会触发

ChangeEvent，您必须另外控制和检查所选选项卡索引（例如使用((JTabbedPane) event.getSource()).getSelectedIndex()

）才能确定选择是否实际更改。

您可以实现这一点，例如通过自定义

ChangeListener

 跟踪当前选定的选项卡并在选择更改时调用特定代码。