Java：遍历 JButton 列表

Question

我的 JPanel 上有一个 JButton 的 ArrayList。 所有按钮都使用 JPanel 上的 GridBagLayout 添加在一条水平线上，如下所示。

这样做是为了让 focusOwner JButton 具有红色背景，而其他 JButton 具有绿色背景。

我想通过用户 keboard 转移焦点。 例如，如果用户单击左箭头，则焦点转移到具有焦点的按钮左侧的按钮。 同样，如果他单击右箭头，焦点将转移到 focusOwner 右侧的按钮。

我还希望如果用户按 Enter 键，则按下 focusOwner 按钮（运行 actionListener）。

Answer 1

使用键绑定为每个JButton注册所需的操作。
使用焦点侦听器更改焦点和非焦点JButton的背景颜色。
使用键盘焦点管理器移动焦点。

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.KeyboardFocusManager;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import java.awt.event.KeyEvent;

import javax.swing.AbstractAction;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.WindowConstants;

public class RedGreen implements ActionListener, FocusListener, Runnable {
    private JFrame  frame;

    public void actionPerformed(ActionEvent event) {
        JOptionPane.showMessageDialog(frame, event.getActionCommand());
    }

    public void focusGained(FocusEvent event) {
        event.getComponent().setBackground(Color.red);
    }

    public void focusLost(FocusEvent event) {
        event.getComponent().setBackground(Color.green);
    }

    @Override
    public void run() {
        showGui();
    }

    private JButton createButton(int index) {
        JButton button = new JButton("Ledger");
        button.setActionCommand(String.valueOf(index));
        button.addActionListener(this);
        button.setBackground(Color.green);
        button.addFocusListener(this);
        InputMap inputMap = button.getInputMap();
        ActionMap actionMap = button.getActionMap();

        KeyStroke enter = KeyStroke.getKeyStroke(KeyEvent.VK_ENTER, 0);
        inputMap.put(enter, "ACTION");
        actionMap.put("ACTION", new EnterAction());

        KeyStroke rightArrow = KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0);
        inputMap.put(rightArrow, "NEXT");
        actionMap.put("NEXT", new RightAction());

        KeyStroke leftArrow = KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0);
        inputMap.put(leftArrow, "PREVIOUS");
        actionMap.put("PREVIOUS", new LeftAction());

        return button;
    }
    private JPanel createButtonsPanel() {
        JPanel panel = new JPanel();
        panel.add(createButton(1));
        panel.add(createButton(2));
        panel.add(createButton(3));
        panel.add(createButton(4));
        return panel;
    }

    private void showGui() {
        frame = new JFrame();
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.add(createButtonsPanel(), BorderLayout.PAGE_END);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new RedGreen());
    }

    private static class EnterAction extends AbstractAction {
        
        @Override
        public void actionPerformed(ActionEvent event) {
            Object source = event.getSource();
            if (source instanceof JButton) {
                JButton button = (JButton) source;
                button.doClick();
            }
        }
    }

    private static class LeftAction extends AbstractAction {

        @Override
        public void actionPerformed(ActionEvent event) {
            KeyboardFocusManager kfm = KeyboardFocusManager.getCurrentKeyboardFocusManager();
            kfm.focusPreviousComponent();
        }
    }

    private static class RightAction extends AbstractAction {

        @Override
        public void actionPerformed(ActionEvent event) {
            KeyboardFocusManager kfm = KeyboardFocusManager.getCurrentKeyboardFocusManager();
            kfm.focusNextComponent();
        }
    }
}