Question

我正在尝试在Applet中开发游戏，我遇到了这个问题。我希望显示器在游戏继续之前向用户显示倒计时。但是，倒计时不会显示，实际上会使GUI冻结。如何避免这种情况？以下是一些证明此问题的代码。

编辑：“几乎”下面的代码正常工作，计时器正在运行但屏幕只会在按下“开始”按钮时更新为新的计时器值。如何自动刷新文本？

public class TestApplet extends JApplet implements ActionListener{


        final JTextField _displayField = new JTextField("Countdown", 6);
        CountDownTimer clock = new CountDownTimer();
        JButton jbtnStart = new JButton("Start");

    public void addComponentToPane(Container pane) {

        JPanel mainPanel = new JPanel();    
        mainPanel.add(jbtnStart);
        mainPanel.add(_displayField);
        pane.add(mainPanel);
        jbtnStart.addActionListener(this);
    }


  public void init() {

        TestApplet testApplet = new TestApplet();
        testApplet.setVisible(true);    
        testApplet.addComponentToPane(this.getContentPane());   
        this.setSize(200, 100);

}

    public void actionPerformed(ActionEvent e) {

      if ( e.getSource() == jbtnStart   ){
              clock.start(_displayField);
          }
   }     
}

// ********************************************************************************
//********************************************************************************
//********************************************************************************

class CountDownTimer  {

    private static final int N = 60;
    private final ClockListener cl = new ClockListener();
    private final Timer t = new Timer(1000, cl);
    static int count =0;

    public int getCount(){
         System.out.println(count);
        return count;
    }
    public void setCount(int n){
        count = n;
    }

    public CountDownTimer() {
        t.setInitialDelay(0);
    }

    public void start(JTextComponent c) {
        t.start();
       Boolean bool  = false;
          while ( bool ==false){     
              c.setText( "Starting new game in... "+ this.getCount() );
              bool = ( this.getCount()<10 );
          }
    }

    private class ClockListener implements ActionListener {

        public void actionPerformed(ActionEvent e) {
            count %= N;
            count++;
           setCount(count);
        }
    }
}

Answer 1

ActionListener中有一个阻止EDT的while循环。更新显示字段的代码不应该在ActionListener中。

相反，此代码应该在Timer类中。然后，只要Timer触发，您只需减去一个并更新显示字段。当计数达到零时，停止计时器。

此外，您的CountDownTimer不应扩展JFrame。它只是一个类，与框架无关。

编辑：

以下是Swing Timer的一个简单用法：

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

public class TimerTime extends JFrame implements ActionListener
{
    JLabel timeLabel;

    public TimerTime()
    {
        timeLabel = new JLabel( new Date().toString() );
        getContentPane().add(timeLabel, BorderLayout.NORTH);
    }

    public void actionPerformed(ActionEvent e)
    {
        timeLabel.setText( new Date().toString() );
    }

    public static void main(String[] args)
    {
        TimerTime frame = new TimerTime();
        frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
        frame.pack();
        frame.setVisible(true);

        int time = 1000;
        javax.swing.Timer timer = new javax.swing.Timer(time, frame);
        timer.setInitialDelay(1);
        timer.start();
    }
}

Answer 2

我们一直在争论是否有可能使用后台线程的解决方案，所以我使用辅助线程编写了一个解决方案，它运行正常。

方法“getCount”和“setCount”是可有可无的

“N”常数稳定倒计时的长度

公共类TestApplet扩展JApplet实现了ActionListener {

JTextField _displayField;
CountDownTimer clock;
JButton jbtnStart;
Thread thread;

public TestApplet(){
    this.jbtnStart = new JButton("Start");
    this._displayField = new JTextField("Countdown", 30);
    this.clock = new CountDownTimer(_displayField);
    this.thread = null;
}

public void addComponentToPane(Container pane) {



    JPanel mainPanel = new JPanel();    
    mainPanel.add(jbtnStart);
    mainPanel.add(_displayField);
    pane.add(mainPanel);
    jbtnStart.addActionListener(this);
}


public void init() {

    TestApplet testApplet = new TestApplet();
    testApplet.setVisible(true);    
    testApplet.addComponentToPane(this.getContentPane());   
    this.setSize(200, 100);


}

public void actionPerformed(ActionEvent e) {

    if ( e.getSource() == jbtnStart   ){

        if(thread != null){
            thread.interrupt();
        }
        thread = new Thread(clock);
        thread.start();
    }
}

}

/ <强> * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * *** / / <强> 的 ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * * / / <强> * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * **** /

public class CountDownTimer implements Runnable{ private static final int N = 60; JTextComponent c; static int count =0; public int getCount(){ System.out.println(count); return count; } public void setCount(int n){ count = n; } public CountDownTimer(JTextComponent c) { this.c = c; } @Override public void run() { try { for(int i=N; i>0; i--){ setCount(i); c.setText( "Starting new game in... "+ this.getCount() ); Thread.sleep(1000); } } catch (InterruptedException e) { e.printStackTrace(); }finally{ setCount(0); } } }

Answer 3

如何使用并发进行倒计时？

        public void actionPerformed(ActionEvent e) {

              if ( e.getSource() == jbtnStart   ){
              //You should start your new thread here
              Thread thread = Thread(new Runnable(){
                 public void run(){
                     clock.start();
                     Boolean bool  = false;
                     while ( bool ==false){
    //You can not modify the UI from a secondary thread, so you should call to some 
    //method in the GUI thread...     
                     _displayField.setText( "Starting new game in... "+ clock.getCount() );
                     bool = ( clock.getCount()==5 );  
                 }

               }
               thread.start();

            }


     }
}

注意：代码是由心脏完成的，所以容易出现一些错误，但它表达了主要观点。

如何防止我的Applet定时器锁定？

3 个答案: