在另一个线程正在运行时执行任务

Question

我目前正在学习Java中的多线程并遇到了一个有趣的问题.我有一个"loader"类,它读取一些CSV文件.

public class LoaderThread implements Runnable{

@Override
public void run(){
//do some fancy stuff
}
}

此外,我有一个SplashScreen,我想在加载数据时显示它.

import javax.swing.JLabel;
import javax.swing.JWindow;
import javax.swing.SwingConstants;

public class SplashScreen extends JWindow{

JWindow jwin = new JWindow();

public SplashScreen(){

jwin.getContentPane().add(new JLabel("Loading...please wait!",SwingConstants.CENTER));
jwin.setBounds(200, 200, 200, 100);

jwin.setLocationRelativeTo(null);

jwin.setVisible(true);

try {
  Thread.sleep(3000);
} catch (InterruptedException e) {
  Thread.currentThread().interrupt(); 
 }

jwin.setVisible(false);
jwin.dispose();

}
}

当用户点击按钮时,代码从我的主类运行:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt)   {                                         


    final Thread t = new Thread() {

           @Override
           public void run() {  

              LoaderThread myRunnable = new LoaderThread();
              Thread myThread = new Thread(myRunnable);
              myThread.setDaemon(true); 
              myThread.start();
              while(myThread.isAlive()==true)
              {
                  SplashScreen ss = new SplashScreen();
              }


           }
        };
        t.start();  // call back run()
        Thread.currentThread().interrupt();         

}                  

此设置正在运行,但是当加载时间超过3秒并且显示至少3秒时,消息"闪烁",即使加载过程可能更短.

我现在想知道只要加载线程正在运行,是否可以显示消息.不再也不短.

提前致谢!

Answer 1

您正在循环中创建新实例,这就是它闪烁的原因.您宁愿创建一个实例,使其可见,当另一个线程完成执行时,请将其丢弃.

Answer 2

这是观察者模式运作良好的完美示例.在Swing中轻松完成此操作的一种方法是使用SwingWorker作为后台线程.执行SwingWorker时显示启动画面.在执行SwingWorker之前,向它添加一个PropertyChangeListener,当它返回SwingWorker.StateValue.DONE时,摆脱启动画面.

此外,不要Thread.sleep(...)像往常一样调用Swing事件线程,因为这是灾难的保证.

编辑1
关于您的评论 -

你是什​​么意思"也不要在Swing事件线程上调用Thread.sleep ......"？你是什​​么意思"也不要在Swing事件线程上调用Thread.sleep ......"？

这是在Swing事件线程上调用的,也称为EDT或E vent D ispatch T hread:

try {
  Thread.sleep(3000);
} catch (InterruptedException e) {
  Thread.currentThread().interrupt(); 
}

这将使您的整个应用程序处于睡眠状态,使其完全无响应,因此建议您不要Thread.sleep(...)在EDT上调用.

编辑2
示例代码:

import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;

import javax.swing.*;

public class SwingWorkerEg extends JPanel {
   private static final int PREF_W = 300;
   private static final int PREF_H = 200;

   public SwingWorkerEg() {
      add(new JButton(new ButtonAction("Press Me")));
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H);
   }

   private static void createAndShowGui() {
      JFrame frame = new JFrame("SwingWorkerEg");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(new SwingWorkerEg());
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

class ButtonAction extends AbstractAction {
   public ButtonAction(String title) {
      super(title);
   }

   @Override
   public void actionPerformed(ActionEvent actEvt) {
      final JButton source = (JButton)actEvt.getSource();
      source.setEnabled(false);
      MySwingWorker mySw = new MySwingWorker();
      final MySplashScreen mySplash = new MySplashScreen();
      mySplash.setVisible(true);

      mySw.addPropertyChangeListener(new PropertyChangeListener() {

         @Override
         public void propertyChange(PropertyChangeEvent pcEvt) {
            if (SwingWorker.StateValue.DONE == pcEvt.getNewValue()) {
               mySplash.setVisible(false);
               mySplash.dispose();
               source.setEnabled(true);
            }
         }
      });
      mySw.execute();
   }
}

class MySwingWorker extends SwingWorker<Void, Void> {
   private static final long SLEEP_TIME = 5 * 1000;

   @Override
   protected Void doInBackground() throws Exception {
      Thread.sleep(SLEEP_TIME); // emulate long-running task
      return null;
   }
}

class MySplashScreen extends JWindow {
   private static final String LABEL_TEXT = "Loading, ... please wait...";
   private static final int PREF_W = 500;
   private static final int PREF_H = 300;

   public MySplashScreen() {
      add(new JLabel(LABEL_TEXT, SwingConstants.CENTER));
      pack();
      setLocationRelativeTo(null);
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H);
   }
}