Question

我打印简单值以使用简单的for循环附加JTextArea，当我运行它时，如果我在控制台输出中打印值，它就会正常运行...

但是如果我在文本区域附加JTextArea并打印值，则在整个程序运行后将它们全部附加。

public class SwingThread {

private JFrame frame;

/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                SwingThread window = new SwingThread();
                window.frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the application.
 */
public SwingThread() {
    initialize();
}

/**
 * Initialize the contents of the frame.
 */
private void initialize() {
    frame = new JFrame();
    frame.setBounds(100, 100, 450, 300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    JScrollPane scrollPane = new JScrollPane();
    frame.getContentPane().add(scrollPane, BorderLayout.CENTER);

    JTextArea textArea = new JTextArea();
    scrollPane.setViewportView(textArea);

    JButton btnNewButton = new JButton("New button");
    scrollPane.setColumnHeaderView(btnNewButton);
    btnNewButton.addActionListener(new ActionListener()
    {
        public void actionPerformed(ActionEvent arg0)
        {
            try
            {
                for(int i = 0 ; i <= 5 ; i++)
                {
                    textArea.append("Value "+i+"\n");
                    System.out.println("Value is" + i);
                    Thread.sleep(1000);
                }
            }
            catch(Exception e)
            {
                System.out.println("Error : "+e);
            }
        }
    });
}
}

我想逐个追加，但是在整个程序运行后附加了它。

Answer 1

您的问题在于使用Thread.sleep，因为当您在Swing事件线程（或事件调度线程的EDT）上调用它时，它将使整个Swing事件线程进入休眠状态。当发生这种情况时，无法执行此线程的操作，包括绘制GUI（更新它）以及与用户交互，这将完全冻结您的GUI - 不好。当前情况下的解决方案是使用Swing Timer作为伪循环。 Timer在后台线程中创建一个循环，并保证其ActionPerformed方法中的所有代码都将在Swing事件线程上调用，这是必需的，因为我们不希望从该线程附加到JTextArea。

正如其他人已经注意到的那样，如果你想要做的就是在Swing中执行延迟重复动作，那么是的，使用这个Swing Timer。另一方面，如果您希望在Swing中运行长时间运行的代码，则此代码将再次阻止EDT并冻结您的程序。对于这种情况，请使用后台线程，例如SwingWorker提供的后台线程。有关详细信息，请查看Lesson: Concurrency in Swing。

如，

btnNewButton.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent arg0) {
        // delay between timer ticks: 1000
        int timerDelay = 1000;
        new Timer(timerDelay, new ActionListener() {
            private int counter = 0;
            @Override
            public void actionPerformed(ActionEvent e) {
                // timer's stopping condition
                if (counter >= MAX_VALUE) { // MAX_VALUE is a constant int = 5
                    ((Timer) e.getSource()).stop();
                } else {
                    textArea.append("Value " + counter + "\n");
                }
                counter++; // increment timer's counter variable
            }
        }).start();
    }
});

整件事：

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.*;

import javax.swing.*;

public class SwingThread2 {
    protected static final int MAX_VALUE = 5; // our constant
    private JFrame frame;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    SwingThread2 window = new SwingThread2();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public SwingThread2() {
        initialize();
    }

    private void initialize() {
        frame = new JFrame();
        // frame.setBounds(100, 100, 450, 300); // avoid this
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JScrollPane scrollPane = new JScrollPane();
        frame.getContentPane().add(scrollPane, BorderLayout.CENTER);

        JTextArea textArea = new JTextArea(15, 40);
        scrollPane.setViewportView(textArea);

        JButton btnNewButton = new JButton("New button");
        scrollPane.setColumnHeaderView(btnNewButton);
        btnNewButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                // delay between timer ticks: 1000
                int timerDelay = 1000;
                new Timer(timerDelay, new ActionListener() {
                    private int counter = 0;
                    @Override
                    public void actionPerformed(ActionEvent e) {
                        // timer's stopping condition
                        if (counter >= MAX_VALUE) { // MAX_VALUE is a constant int = 5
                            ((Timer) e.getSource()).stop();
                        } else {
                            textArea.append("Value " + counter + "\n");
                        }
                        counter++; // increment timer's counter variable
                    }
                }).start();
            }
        });

        // better to avoid setting sizes but instead to
        // let the components size themselves vis pack
        frame.pack();
        frame.setLocationRelativeTo(null);
    }
}

仅供参考，以下是上述相同程序的示例，该程序使用SwingWorker执行长时间运行操作，然后使用此操作更新JProgressBar。工作者非常简单，只需使用while循环就可以通过有限的随机数推进计数器变量。然后它传输使用这个值来更新它自己的progress属性（一个只能从0到100的值，因此在其他情况下，需要对该值进行规范化以符合这一点）。我将一个PropertyChangeListener附加到worker，每当工作程序的进度值发生更改时，以及SwingWorker更改状态时（例如操作完成时），都会在Swing事件线程上通知。在后一种情况下，worker的StateValue变为StateValue.DONE。然后，侦听器相应地更新GUI。如果有任何问题，请询问。

import java.awt.BorderLayout; import java.awt.EventQueue; import java.awt.event.*; import java.beans.PropertyChangeEvent; import java.beans.PropertyChangeListener; import java.util.Random; import java.util.concurrent.ExecutionException; import javax.swing.*; public class SwingThread2 { protected static final int MAX_VALUE = 5; // our constant private JFrame frame; private JProgressBar progressBar = new JProgressBar(); public static void main(String[] args) { EventQueue.invokeLater(new Runnable() { public void run() { try { SwingThread2 window = new SwingThread2(); window.frame.setVisible(true); } catch (Exception e) { e.printStackTrace(); } } }); } public SwingThread2() { initialize(); } private void initialize() { frame = new JFrame(); // frame.setBounds(100, 100, 450, 300); // avoid this frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JScrollPane scrollPane = new JScrollPane(); frame.getContentPane().add(scrollPane, BorderLayout.CENTER); JTextArea textArea = new JTextArea(15, 40); scrollPane.setViewportView(textArea); JButton btnNewButton = new JButton("New button"); scrollPane.setColumnHeaderView(btnNewButton); btnNewButton.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent arg0) { // delay between timer ticks: 1000 int timerDelay = 1000; new Timer(timerDelay, new ActionListener() { private int counter = 0; @Override public void actionPerformed(ActionEvent e) { // timer's stopping condition if (counter >= MAX_VALUE) { // MAX_VALUE is a constant // int = 5 ((Timer) e.getSource()).stop(); } else { textArea.append("Value " + counter + "\n"); } counter++; // increment timer's counter variable } }).start(); } }); progressBar.setStringPainted(true); JPanel bottomPanel = new JPanel(); bottomPanel.setLayout(new BoxLayout(bottomPanel, BoxLayout.LINE_AXIS)); bottomPanel.add(new JButton(new MyAction("Press Me"))); bottomPanel.add(progressBar); frame.getContentPane().add(bottomPanel, BorderLayout.PAGE_END); // better to avoid setting sizes but instead to // let the components size themselves vis pack frame.pack(); frame.setLocationRelativeTo(null); } private class MyAction extends AbstractAction { public MyAction(String name) { super(name); int mnemonic = (int) name.charAt(0); putValue(MNEMONIC_KEY, mnemonic); } public void actionPerformed(ActionEvent e) { progressBar.setValue(0); setEnabled(false); MyWorker myWorker = new MyWorker(); myWorker.addPropertyChangeListener(new WorkerListener(this)); myWorker.execute(); } } private class WorkerListener implements PropertyChangeListener { private Action action; public WorkerListener(Action myAction) { this.action = myAction; } @Override public void propertyChange(PropertyChangeEvent evt) { if ("progress".equals(evt.getPropertyName())) { int progress = (int) evt.getNewValue(); progressBar.setValue(progress); } else if ("state".equals(evt.getPropertyName())) { if (evt.getNewValue() == SwingWorker.StateValue.DONE) { action.setEnabled(true); @SuppressWarnings("rawtypes") SwingWorker worker = (SwingWorker) evt.getSource(); try { // always want to call get to trap and act on // any exceptions that the worker might cause // do this even though get returns nothing worker.get(); } catch (InterruptedException | ExecutionException e) { e.printStackTrace(); } } } } } private class MyWorker extends SwingWorker<Void, Void> { private static final int MULTIPLIER = 80; private int counter = 0; private Random random = new Random(); @Override protected Void doInBackground() throws Exception { while (counter < 100) { int increment = random.nextInt(10); Thread.sleep(increment * MULTIPLIER); counter += increment; counter = Math.min(counter, 100); setProgress(counter); } return null; } } }

为什么我的线程在Swing中无法正常工作？

1 个答案: