java 嵌套的 e.getActionCommand 不工作

Question

我刚开始学习 Java GUI，正如标题所说，我对 getActionCommand 有疑问。它是微波模拟。当倒计时正在运行并且用户按下停止时，它将计时器重置为 0(或空字符串)。 CountF 是一个 JLabel，而 startB 是一个 JButton。任何帮助将不胜感激

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

    public class Countdown extends JFrame implements ActionListener
    {

    private JLabel countF;
    private JButton oneB;
    private JButton twoB;
    private JButton threeB;
    private JButton fourB;
    private JButton fiveB;
    private JButton sixB;
    private JButton sevenB;
    private JButton eightB;
    private JButton nineB;
    private JButton zeroB;
    private JButton startB;
    private JButton openB;
    private int cookingSeconds;
    private int time;

    public static void main(String[] args)
    {
        Countdown demoGui = new Countdown( );
        demoGui.setVisible(true);
    }
    public Countdown()
    {
        super("Microwave");
        this.setSize(700, 400);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setLayout(new GridLayout(1,2));
        add(new JLabel("Food to be heated"));
        JPanel rightP = new JPanel();
        add(rightP);
        rightP.setLayout(new BorderLayout());
        JPanel textP = new JPanel();
        textP.setPreferredSize(new Dimension(300, 50));
        textP.setBackground(Color.WHITE);
        countF = new JLabel();
        textP.add(countF);
        rightP.add(textP, BorderLayout.NORTH);
        JPanel tempP = new JPanel();
        rightP.add(tempP, BorderLayout.CENTER);
        tempP.setLayout(new GridLayout(4,3));
        oneB = new JButton("1");
        tempP.add(oneB);
        twoB = new JButton("2");
        tempP.add(twoB);
        threeB = new JButton("3");
        tempP.add(threeB);
        fourB = new JButton("4");
        tempP.add(fourB);
        fiveB = new JButton("5");
        tempP.add(fiveB);
        sixB = new JButton("6");
        tempP.add(sixB);
        sevenB = new JButton("7");
        tempP.add(sevenB);
        eightB = new JButton("8");
        tempP.add(eightB);
        nineB = new JButton("9");
        tempP.add(nineB);
        zeroB = new JButton("0");
        tempP.add(zeroB);
        startB = new JButton("Start");
        tempP.add(startB);
        openB = new JButton("Open");
        tempP.add(openB);
        startB.addActionListener(this);
        openB.addActionListener(this);
        oneB.addActionListener(this);
        twoB.addActionListener(this);
        threeB.addActionListener(this);
        fourB.addActionListener(this);
        fiveB.addActionListener(this);
        sixB.addActionListener(this);
        sevenB.addActionListener(this);
        eightB.addActionListener(this);
        nineB.addActionListener(this);
        zeroB.addActionListener(this);
    }
    public void setCountDownLabelText(String text)
    {
        countF.setText(text);
    }
    public void setOpenBEnable()
    {
        openB.setEnabled(true);
        oneB.setEnabled(true);
        twoB.setEnabled(true);
        threeB.setEnabled(true);
        fourB.setEnabled(true);
        fiveB.setEnabled(true);
        sixB.setEnabled(true);
        sevenB.setEnabled(true);
        eightB.setEnabled(true);
        nineB.setEnabled(true);
        zeroB.setEnabled(true);
    }

    //you need to add the event handling for 1, 2, ...9, 0 buttons to calculate the cookingSeconds.
    public void actionPerformed(ActionEvent e)
    {
        if(e.getSource() == startB)
        {
            time = Integer.parseInt(countF.getText());
            cookingSeconds = time;
            new CountDownTimer(this, cookingSeconds).start();
            startB.setText("Stop");
            openB.setEnabled(false);
            oneB.setEnabled(false);
            twoB.setEnabled(false);
            threeB.setEnabled(false);
            fourB.setEnabled(false);
            fiveB.setEnabled(false);
            sixB.setEnabled(false);
            sevenB.setEnabled(false);
            eightB.setEnabled(false);
            nineB.setEnabled(false);
            zeroB.setEnabled(false);
            if(e.getActionCommand().equals("Stop"))
            {
                // this is not working
                countF.setText("");
            }
        }
        else if (e.getSource() == openB)
        {
            countF.setText("");
        }
        else if (e.getSource() == oneB)
        {
            countF.setText(countF.getText() + "1");
        }
        else if (e.getSource() == twoB)
        {
            countF.setText(countF.getText() + "2");
        }
        else if (e.getSource() == threeB)
        {
            countF.setText(countF.getText() + "3");
        }
        else if (e.getSource() == fourB)
        {
            countF.setText(countF.getText() + "4");
        }
        else if (e.getSource() == fiveB)
        {
            countF.setText(countF.getText() + "5");
        }
        else if (e.getSource() == sixB)
        {
            countF.setText(countF.getText() + "6");
        }
        else if (e.getSource() == sevenB)
        {
            countF.setText(countF.getText() + "7");
        }
        else if (e.getSource() == eightB)
        {
            countF.setText(countF.getText() + "8");
        }
        else if (e.getSource() == nineB)
        {
            countF.setText(countF.getText() + "9");
        }
        else if (e.getSource() == zeroB)
        {
            countF.setText(countF.getText() + "0");
        }
    }
}

Answer 1

您必须从 Button 获取 ActionCommand 的值，同时您从事件中获取它，这会给您旧值，因为您是在 if block 中设置文本，因为您还需要在该点上设置 setActionCommand。

 if("Stop".equals(startB.getActionCommand())){//To avoid NullPointer
       countF.setText("");
 }