FocusListener & JOptionPane

Question

这是我的简单程序的代码。有四个textFields。当光标在第一个textField上时，JOptionPane被创建，当我按ok游标移动到下一个字段，再次创建OptionPane时，当游标位于第四个字段时，单击OptionPane上的OK，光标移动到第五个字段"f“。当光标在字段中时，我在数组中打印字段的位置:System.out.println(“第一或第二或第三或第四”)

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class Hello extends JFrame implements ActionListener, FocusListener {

    public JTextField[] fields = new JTextField[4];
    public JPanel panel = new JPanel();
    public JTextField f = new JTextField(12);
    public static void main(String[] args) {
        new Hello();
    }

    public Hello() {
        for (int i = 0; i < 4; i++) {
            fields[i] = new JTextField(12);
            fields[i].addFocusListener(this);
            panel.add(fields[i]);
        }
        add(panel);
        add(f);
        setTitle("Hello World");
        getContentPane().setLayout(new BoxLayout(getContentPane(), BoxLayout.PAGE_AXIS));
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(920, 420);
        setLocation(100, 100);
        setVisible(true);
    }

    @Override
    public void actionPerformed(ActionEvent ae) {
    }

    @Override
    public void focusGained(FocusEvent fe) {
        if (fe.getSource() == fields[0]) {
             JOptionPane.showMessageDialog(null, "HELLO");             
            fields[1].requestFocus();
            System.out.println("FIRST");
        } else if (fe.getSource() == fields[1]) {
             JOptionPane.showMessageDialog(null, "HELLO");           
            fields[2].requestFocus();
            System.out.println("SECOND");
        } else if (fe.getSource() == fields[2]) {
             JOptionPane.showMessageDialog(null, "HELLO");            
            fields[3].requestFocus();
            System.out.println("THIRD");
        } else if (fe.getSource() == fields[3]) {
             JOptionPane.showMessageDialog(null, "HELLO");          
              f.requestFocus();
                System.out.println("FOURTH")
        }
    }

    @Override
    public void focusLost(FocusEvent fe) {
    }
}

当没有OptionPane时，光标从第一个字段向前移动到第四个字段并打印：

FIRST
SECOND
THIRD
FOURTH

但是，当有JOptionPane时，输出是：

FIRST
SECOND
FIRST
SECOND
THIRD
SECOND
THIRD
FOURTH
THIRD
FOURTH
FOURTH

可以看出，在第二场之后，它回到了第一场，在第三场之后，它又回到了第二场，而不是第四场之后，它又回到了第三场。

我想知道为什么？我该怎么解决这个问题

Answer 1

问题是，每次单击JOptionPane上的OK时，焦点将返回到显示JOptionPane之前的最后一个JOptionPane活动，因此将向该控件的事件队列中添加一个新的requestFocus事件。实际上，在第一次执行代码时单击OK之后，会触发几个对话框，只是看不到它，因为每次都显示相同的文本(HELLO)。我已经修改了你的代码让它正常工作。希望能帮上忙！

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import java.util.ArrayList;
import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class testOptionPane extends JFrame implements ActionListener, FocusListener {

    public ArrayList<JTextField> fields = new ArrayList<>();
    public JPanel panel = new JPanel();
    public JTextField f = new JTextField(12);
    private int currentField = 0;
    private boolean focusReturned = false;
    public static void main(String[] args) {
        new testOptionPane();
    }

    public testOptionPane() {
        for (int i = 0; i < 4; i++) {
            JTextField tf = new JTextField(12);
            fields.add(tf);
            tf.addFocusListener(this);
            panel.add(tf);
        }
        add(panel);
        fields.add(f);
        add(f);
        setTitle("Hello World");
        getContentPane().setLayout(new BoxLayout(getContentPane(), BoxLayout.PAGE_AXIS));
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(920, 420);
        setLocation(100, 100);
        setVisible(true);
    }

    @Override
    public void actionPerformed(ActionEvent ae) {
    }

    @Override
    public void focusGained(FocusEvent fe) {
        if (fe.getSource() == fields.get(currentField)) {
            if (!focusReturned) {
                JOptionPane.showMessageDialog(this, "focus on field " + String.valueOf(currentField));
                System.out.println(currentField);
                focusReturned = true;
            } else {
                currentField++;
                focusReturned = false;
                if (currentField < fields.size()) {
                    fields.get(currentField).requestFocus();
                }
            }
        }
    }

    @Override
    public void focusLost(FocusEvent fe) {
    }
}