程式扎記

來源自這裡
Preface:
在使用 Java Swing 開發 UI 程式時, 有時候需要進行耗時工作時, 可以使用 Progress bar 提示使用者目前工作進度或是告訴使用者目前程式的工作狀態.

Demo Code:
下面代碼執行會開啟一個 UI, 並在上面顯示 Progress bar. 在背景使用 SwingWorker (類別 UpdateWorker) 動態的更新 Progress bar 的進度條:

當進度條上的數字達到 100, 則 SwingWorker 方法 done() 會被執行並關閉 UI 與結束程式.

Implementation:

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package swing.demo;  
  
import java.awt.BorderLayout;  
import java.awt.Container;  
import java.util.Random;  
  
import javax.swing.BorderFactory;  
import javax.swing.JFrame;  
import javax.swing.JProgressBar;  
import javax.swing.SwingWorker;  
import javax.swing.border.Border;  
  
public class ProgressSample {  
    public static void main(String args[]) {  
        JFrame f = new JFrame("JProgressBar Sample");  
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
        Container content = f.getContentPane();  
        JProgressBar progressBar = new JProgressBar();  
        progressBar.setValue(0);  
        progressBar.setStringPainted(true);  
        Border border = BorderFactory.createTitledBorder("Reading...");  
        progressBar.setBorder(border);  
        content.add(progressBar, BorderLayout.NORTH);  
        f.setSize(300, 100);  
        f.setVisible(true);  
        UpdateWorker updateWorker = new UpdateWorker(f, progressBar);  
        updateWorker.execute();  
    }  
      
    public static class UpdateWorker extends SwingWorker   
    {  
        JProgressBar bar = null;  
        JFrame f=null;  
        public UpdateWorker(JFrame f, JProgressBar bar)  
        {  
            this.bar = bar;  
            this.f = f;  
        }         
          
        @Override  
        protected String doInBackground() throws Exception {  
            Random rdm = new Random();  
            int pv = 0;  
            while(pv<100)  
            {  
                Thread.sleep(rdm.nextInt(500)+500);  
                pv+=rdm.nextInt(5);  
                bar.setValue(pv);  
            }  
            return null;  
        }   
          
        @Override    
        protected void done()   
        {   
            f.setVisible(false);      
            f.dispose();  
        }  
    }  
}  

Supplement:
* The Java Tutorial > How to Use Progress Bars

Sometimes a task running within a program might take a while to complete. A user-friendly program provides some indication to the user that the task is occurring, how long the task might take, and how much work has already been done. One way of indicating work, and perhaps the amount of progress, is to use an animated image...

* [ Java 代碼範本 ] SwingWorker Example

來源自這裡
Preface :
當我們開發 Swing 程式需要執行需耗時的工作時, 可以使用 worker thread (或稱為 background threads). 而這樣的 worker thread 可以使用類別 javax.swing.SwingWorker 來完成. 它是抽象類別, 要使用時可以繼承該類別, 並實作方法 doInBackground(), 並在裡面執行耗時工作.

Demo Code:
下面的範例代碼會建立一個 UI 如下:

點擊按鈕 "Start" 將會建立 NumberWorker 的物件, 它實作 javax.swing.SwingWorker, 接著會執行你實作方法 doInBackground() 的代碼, 而當背景程式正在執行時你可以任意移動該 UI, 甚至可以在 TextField 上面輸入字串; 而在你從該方法透出後, 方法 done() 會被執行:

而在背景程式 done() 方法中, 會將取得的 random number 設回原來 UI 的 TextField 並完成背景工作.

當你在點擊按鈕 "Start" 後, 按鈕 "Cancel" 將會被 enable. 當你點擊 "Cancel" 按鈕, 在 "Start" 按鈕點擊後建立的 NumberWorker 的物件上的方法 cancel(true) (繼承來自 SwingWorker 上面方法)將會被執行, 並同時終止正在背景執行的工作.

Implementation:

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package swing.demo;  
  
import java.awt.BorderLayout;  
import java.awt.Dimension;  
import java.awt.FlowLayout;  
import java.awt.GridLayout;  
import java.awt.event.ActionEvent;  
import java.awt.event.ActionListener;  
import java.util.Random;  
  
import javax.swing.ImageIcon;  
import javax.swing.JButton;  
import javax.swing.JFrame;  
import javax.swing.JLabel;  
import javax.swing.JPanel;  
import javax.swing.JTextField;  
import javax.swing.SwingUtilities;  
import javax.swing.SwingWorker;  
import javax.swing.WindowConstants;  
  
  
public class LuckyNumber extends JFrame implements ActionListener{  
    private static final long serialVersionUID = 4276832367310733568L;  
    private JLabel label;  
    private JButton cancel;  
    private JButton start;  
    private SwingWorker worker;  
    private JTextField textField;  
  
    public LuckyNumber() {  
        JPanel panel = new JPanel();  
        panel.setLayout(new GridLayout(2, 1));  
  
        JPanel buttons = new JPanel(new FlowLayout());  
        start = new JButton("Start");  
        start.addActionListener(this);  
        start.setDefaultCapable(true);  
        buttons.add(start);  
        cancel = new JButton("Cancel");  
        cancel.setEnabled(false);  
        cancel.addActionListener(this);  
        buttons.add(cancel);  
        panel.add(buttons);  
  
        ImageIcon image = new ImageIcon(getClass().getClassLoader().getResource("swing/demo/images/spinner.gif"));        
  
        label = new JLabel(image);  
        JPanel answer = new JPanel(new GridLayout(1, 2));  
        textField = new JTextField("");  
        answer.add(textField);  
        answer.add(label);  
        label.setVisible(false);  
        panel.add(answer);  
  
        setTitle("Lucky number generator");  
        setPreferredSize(new Dimension(300, 100));  
        getContentPane().setLayout(new BorderLayout());  
        getContentPane().add(panel);  
  
    }  
  
    public static void main(String[] args) {  
        SwingUtilities.invokeLater(new Runnable() {  
            public void run() {  
                LuckyNumber luckyNumber = new LuckyNumber();  
                luckyNumber.pack();  
                luckyNumber.setVisible(true);  
                luckyNumber.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);  
            }  
        });  
    }  
  
    public void actionPerformed(ActionEvent e) {  
        if (e.getSource() == start) {  
            start.setEnabled(false);  
            textField.setText("");  
            worker = new NumberWorker();  
            worker.execute();  
            label.setVisible(true);  
            cancel.setEnabled(true);  
        } else if (e.getSource() == cancel) {  
            cancel();  
        }  
  
    }  
  
    @Override  
    public void dispose() {  
        cancel();  
        super.dispose();  
    }  
  
    private void cancel() {  
        start.setEnabled(true);  
        label.setVisible(false);  
        cancel.setEnabled(false);  
        if (worker != null) {  
            worker.cancel(true);  
            worker = null;  
        }  
  
    }  
  
    private class NumberWorker extends SwingWorker {  
  
        private Random r = new Random();  
  
        @Override  
        protected String doInBackground() throws Exception {  
            long s = System.currentTimeMillis();  
            while (System.currentTimeMillis() - s < 5000 && !Thread.currentThread().isInterrupted()) {  
                r.nextInt();  
            }  
            return String.valueOf(r.nextInt(10) + 1);  
        }  
  
        @Override  
        protected void done() {  
            try {  
                textField.setText(get());  
                LuckyNumber.this.worker = null;  
                LuckyNumber.this.cancel();  
            } catch (Exception ignore) {  
            }  
        }  
    }  
}  

Supplement:
* The Java Tutorial > Worker Threads and SwingWorker

When a Swing program needs to execute a long-running task, it usually uses one of the worker threads, also known as the background threads. Each task running on a worker thread is represented by an instance of javax.swing.SwingWorker. SwingWorker itself is an abstract class; you must define a subclass in order to create a SwingWorker object; anonymous inner classes are often useful for creating very simple SwingWorker objects.

程式扎記

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2012年10月29日星期一

[ Java 代碼範本 ] UI - Progress bar sample code

2012年10月28日星期日

[ Java 代碼範本 ] SwingWorker Example

[Git 常見問題] error: The following untracked working tree files would be overwritten by merge

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2012年10月29日 星期一