進度條與線程（的Java Swing）

Question

這裏是一個小一例子：

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {           
     int x = 0; 
     while (jProgressBar1.getValue() < 100) { 
      try { 
       Thread.sleep(50); 
       x++; 
       jProgressBar1.setValue(x); 
       jProgressBar1.repaint(); 
      } catch (InterruptedException ex) { 
       Logger.getLogger(MainWindow.class.getName()).log(Level.SEVERE, null, ex); 
      } 
      System.out.println(jProgressBar1.getValue()); 
     } 
    } 

System.out.println(jProgressBar1.getValue());回到位數IDE輸出，但jProgressBar1不畫這個值。這段代碼有什麼問題？請幫忙。

Answer 1

在Swing線程中不要使用Thread.sleep（）方法。改爲使用javax.swing.Timer。

例子：

private void jButton1ActionPerformed(ActionEvent evt) {           
    final Timer t = new Timer(50, new ActionListener() { 
     public void actionPerformed(ActionEvent e) { 
      jProgressBar1.setValue(jProgressBar1.getValue() + 1); 
      if (jProgressBar1.getValue() == 100) { 
       ((Timer) e.getSource()).stop(); 
      } 
     } 
    }); 
    t.start(); 
} 

Answer 2

問題是，你正在調用.repaint()在你正在做「工作」（Thread.sleep）的同一線程中。 "repaint() does not invoke paint() directly. It schedules a call to an intermediate method, update(). Finally, update() calls paint()..."。這意味着你正在安排一堆repaint()調用，但它們沒有被處理。我還會打賭，一旦數值達到100，進度條就跳到滿了，這是因爲主線程已經結束，所有的repaint()調用終於被處理了。

爲了使jProgressBars的工作，你必須讓他們的重新繪製發生在一個不同的線程比你在做的工作（其中值得注意的也應該是在不同的線程 - 這對大多數Swing更新也是如此）。嘗試在一個新的線程開始此Runnable接口調用代碼之前：

public class ProgressBarPainter implements Runnable{ 
    public JProgressBar jProgressBar1; 
    public void run(){ 
     while(true){ 
      try { 
       Thread.sleep(50); 
       jProgressBar1.repaint(); 
      } catch (InterruptedException ex) { 
       break; 
      } 
     } 
    } 
} 

例功能代碼使用上述：

public class Frame extends JFrame { 

    private static final long serialVersionUID = 1L; 
    private JProgressBar bar; 

    public Frame(){ 
     JPanel contentPanel = (JPanel) getContentPane(); 

     JButton b = new JButton("Do Process"); 
     b.addActionListener(new ActionListener(){ 

      @Override 
      public void actionPerformed(ActionEvent e) { 
       ProgressBarPainter p = new ProgressBarPainter(); 
       p.jProgressBar1 = bar; //Fill in with the bar you want painted 
       Thread t = new Thread(p); 
       t.start(); 

       Worker w = new Worker(); 
       w.jProgressBar1 = bar; 
       Thread t2 = new Thread(w); 
       t2.start(); 
      } 

     }); 
     contentPanel.add(b, BorderLayout.SOUTH); 

     bar = new JProgressBar(); 
     contentPanel.add(bar, BorderLayout.CENTER); 

     pack(); 
     setDefaultCloseOperation(EXIT_ON_CLOSE); 
     setVisible(true); 
    } 

    public static void main(String[] args) { 
     new Frame(); 
    } 

} 

class Worker implements Runnable{ 
    public JProgressBar jProgressBar1; 
    public void run(){ 
     int x = 0; 
     while(jProgressBar1.getValue() != jProgressBar1.getMaximum()){ 
      try { 
       //Do some work 
       Thread.sleep(50); 
       //Update bar 
       jProgressBar1.setValue(x++); 
      } catch (InterruptedException ex) { 
       break; 
      } 
     } 
    } 
} 

class ProgressBarPainter implements Runnable{ 
    public JProgressBar jProgressBar1; 
    public void run(){ 
     while(true){ 
      try { 
       Thread.sleep(50); 
       jProgressBar1.repaint(); 
      } catch (InterruptedException ex) { 
       break; 
      } 
     } 
    } 
}