swing与线程:
1.如果一个动作需要花费很长时间,在一个独立的工作线程中坐这个事情,不要在事件分配线程中做。
意思是可以在事件分配的线程中另起一个线程做这个事情。
2.除了事件分配线程,不要再任何线程中接触swing组件。
如果一个耗时的任务,在过程中要更新GUI上的进度显示。但是由于这个耗时的工作线程不能接触GUI,如何解决?
可以使用EventQueue类的invokeLater(),和invokeAndWait()中实行。
这两个方法的区别是invokeLater()会立即返回,而invokeAndWait()会等待执行完之后返回。
e.g:下面的示范,如果接连按good按钮程序不会出现异常,但是接连按bad按钮会出现异常。
package v1ch14.SwingThreadTest;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
/**
* This program demonstrates that a thread that runs in parallel with the event dispatch thread can
* cause errors in Swing components.
* @version 1.23 2007-05-17
* @author Cay Horstmann
*/
public class SwingThreadTest
{
public static void main(String[] args)
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
SwingThreadFrame frame = new SwingThreadFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
});
}
}
/**
* This frame has two buttons to fill a combo box from a separate thread. The "Good" button uses the
* event queue, the "Bad" button modifies the combo box directly.
*/
class SwingThreadFrame extends JFrame
{
public SwingThreadFrame()
{
setTitle("SwingThreadTest");
final JComboBox combo = new JComboBox();
combo.insertItemAt(Integer.MAX_VALUE, 0);
combo.setPrototypeDisplayValue("set...");
combo.setSelectedIndex(0);
JPanel panel = new JPanel();
JButton goodButton = new JButton("Good");
goodButton.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent event)
{
new Thread(new GoodWorkerRunnable(combo)).start();
}
});
panel.add(goodButton);
JButton badButton = new JButton("Bad");
badButton.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent event)
{
new Thread(new BadWorkerRunnable(combo)).start();
}
});
panel.add(badButton);
panel.add(combo);
add(panel);
pack();
}
}
/**
* This runnable modifies a combo box by randomly adding and removing numbers. This can result in
* errors because the combo box methods are not synchronized and both the worker thread and the
* event dispatch thread access the combo box.
*/
class BadWorkerRunnable implements Runnable
{
public BadWorkerRunnable(JComboBox aCombo)
{
combo = aCombo;
generator = new Random();
}
public void run()
{
try
{
while (true)
{
int i = Math.abs(generator.nextInt());
if (i % 2 == 0) combo.insertItemAt(i, 0);
else if (combo.getItemCount() > 0) combo.removeItemAt(i % combo.getItemCount());
Thread.sleep(1);
}
}
catch (InterruptedException e)
{
}
}
private JComboBox combo;
private Random generator;
}
/**
* This runnable modifies a combo box by randomly adding and removing numbers. In order to ensure
* that the combo box is not corrupted, the editing operations are forwarded to the event dispatch
* thread.
*/
class GoodWorkerRunnable implements Runnable
{
public GoodWorkerRunnable(JComboBox aCombo)
{
combo = aCombo;
generator = new Random();
}
public void run()
{
try
{
while (true)
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
int i = Math.abs(generator.nextInt());
if (i % 2 == 0) combo.insertItemAt(i, 0);
else if (combo.getItemCount() > 0) combo.removeItemAt(i
% combo.getItemCount());
}
});
Thread.sleep(1);
}
}
catch (InterruptedException e)
{
}
}
private JComboBox combo;
private Random generator;
}
在java6中,这样的类已经写进了类库,就是swingWorker<T,V>类,T是工作器线程的返回值,V是想过程方法传递的参数。
e.g:
package v1ch14.SwingWorkerTest;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;
import java.util.List;
import java.util.concurrent.*;
import javax.swing.*;
/**
* This program demonstrates a worker thread that runs a potentially time-consuming task.
* @version 1.1 2007-05-18
* @author Cay Horstmann
*/
public class SwingWorkerTest
{
public static void main(String[] args) throws Exception
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
JFrame frame = new SwingWorkerFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
});
}
}
/**
* This frame has a text area to show the contents of a text file, a menu to open a file and cancel
* the opening process, and a status line to show the file loading progress.
*/
class SwingWorkerFrame extends JFrame
{
public SwingWorkerFrame()
{
chooser = new JFileChooser();
chooser.setCurrentDirectory(new File("."));
textArea = new JTextArea();
add(new JScrollPane(textArea));
setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
statusLine = new JLabel(" ");
add(statusLine, BorderLayout.SOUTH);
JMenuBar menuBar = new JMenuBar();
setJMenuBar(menuBar);
JMenu menu = new JMenu("File");
menuBar.add(menu);
openItem = new JMenuItem("Open");
menu.add(openItem);
openItem.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent event)
{
// show file chooser dialog
int result = chooser.showOpenDialog(null);
// if file selected, set it as icon of the label
if (result == JFileChooser.APPROVE_OPTION)
{
textArea.setText("");
openItem.setEnabled(false);
textReader = new TextReader(chooser.getSelectedFile());
textReader.execute();
cancelItem.setEnabled(true);
}
}
});
cancelItem = new JMenuItem("Cancel");
menu.add(cancelItem);
cancelItem.setEnabled(false);
cancelItem.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent event)
{
textReader.cancel(true);
}
});
}
private class ProgressData
{
public int number;
public String line;
}
private class TextReader extends SwingWorker<StringBuilder, ProgressData>
{
public TextReader(File file)
{
this.file = file;
}
// the following method executes in the worker thread; it doesn't touch Swing components
@Override
public StringBuilder doInBackground() throws IOException, InterruptedException
{
int lineNumber = 0;
Scanner in = new Scanner(new FileInputStream(file));
while (in.hasNextLine())
{
String line = in.nextLine();
lineNumber++;
text.append(line);
text.append("\n");
ProgressData data = new ProgressData();
data.number = lineNumber;
data.line = line;
publish(data);
Thread.sleep(1); // to test cancellation; no need to do this in your programs
}
return text;
}
// the following methods execute in the event dispatch thread
@Override
public void process(List<ProgressData> data)
{ //事件线程也就是中间过程,这里为什么是list呢,因为publish方法的参数时可变数组,而且由publish方法传过来的数据可能不是同一个蘋率,所以当运行这个方法的时候可能publish已经运行了很多次,所以是list参数不是单个参数
if (isCancelled()) return;
StringBuilder b = new StringBuilder();
statusLine.setText("" + data.get(data.size() - 1).number);
for (ProgressData d : data)
{
b.append(d.line);
b.append("\n");
}
textArea.append(b.toString());
}
@Override
public void done()
{
try
{
StringBuilder result = get();//这里得到的是doInBackground方法的返回的值,也就是工作器线程的返回值。
textArea.setText(result.toString()); //可以操作GUI
statusLine.setText("Done");
}
catch (InterruptedException ex)
{
}
catch (CancellationException ex)
{
textArea.setText("");
statusLine.setText("Cancelled");
}
catch (ExecutionException ex)
{
statusLine.setText("" + ex.getCause());
}
cancelItem.setEnabled(false);
openItem.setEnabled(true);
}
private File file;
private StringBuilder text = new StringBuilder();
};
private JFileChooser chooser;
private JTextArea textArea;
private JLabel statusLine;
private JMenuItem openItem;
private JMenuItem cancelItem;
private SwingWorker<StringBuilder, ProgressData> textReader;
public static final int DEFAULT_WIDTH = 450;
public static final int DEFAULT_HEIGHT = 350;
}
主要实现了上面的EventQueue类的invokeLater(),和invokeAndWait()的代替:
doInBackground()方法来实现后台的工作线程。
process(List<V> data) 这一方法来处理分配线程中的中间进度数据。可在这里实现对gui 的操作。
void publish(v... data)传递中间数据到事件线程。在工作线程中可以调用它
viod execute() 为工作器线程的执行预定这个工作器(启动工作器线程)。
SwingWorker.StateValue getState得到这个工作器线程的状态。
但是也有一些意外:
1。可以在任一个线程中添加或移除事件监听器
2。有些Swing方法时线程安全的
JTextComponent.setText
JTextArea.insert
JTextArea.append
JTextArea.replaceRange
JComponent.repaint
JComponent.revalidate
Swing的设计者认为除了事件分配线程之外,从任何其它线程访问组件永远都是不安全的。因此你需要在事件分配线程中构建用户界面。