Java：遍歷 JButton 列表

Question

我的 JPanel 上有一個 JButton 的 ArrayList。 所有按鈕都使用 JPanel 上的 GridBagLayout 添加在一條水平線上，如下所示。

這樣做是為了讓 focusOwner JButton 具有紅色背景，而其他 JButton 具有綠色背景。

我想通過用戶 keboard 轉移焦點。 例如，如果用戶單擊左箭頭，則焦點轉移到具有焦點的按鈕左側的按鈕。 同樣，如果他單擊右箭頭，焦點將轉移到 focusOwner 右側的按鈕。

我還希望如果用戶按 Enter 鍵，則按下 focusOwner 按鈕（運行 actionListener）。

Answer 1

使用鍵綁定為每個JButton注冊所需的操作。
使用焦點偵聽器更改焦點和非焦點JButton的背景顏色。
使用鍵盤焦點管理器移動焦點。

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();
        }
    }
}