为什么我的线程在 Swing 中不能正常工作？

Question

我正在打印简单的值以使用简单的 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，它会正确运行...

但如果我在文本区域附加JTextArea 并打印值，它们会在整个程序运行后全部附加。

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);
            }
        }
    });
}
}

我想一个一个追加，但是是整个程序运行后才追加的。

Answer 1

您的问题在于您使用了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 事件线程进入睡眠状态。发生这种情况时，无法执行该线程的操作，包括绘制 GUI（更新它）和与用户交互，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，这是必要的，因为我们不想附加到该线程之外的 JTextArea。

正如其他人所指出的，如果您只想在 Swing 中执行重复动作并延迟，那么可以，使用此 Swing Timer。另一方面，如果您希望在 Swing 中运行一段长时间运行的代码，那么此代码将再次阻塞 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。请查看Lesson: Concurrency in Swing 了解更多信息。

例如，

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);
    }
}

只是为了获得更多信息，这里是上面相同程序的示例，它使用 SwingWorker 执行长时间运行的操作，然后使用此操作更新 JProgressBar。 worker 非常简单，只需使用 while 循环将计数器变量推进有界随机量。然后它使用这个值来更新它自己的进度属性（这个值只能是从 0 到 100，所以在其他情况下，这个值需要被规范化以符合这个）。我将 PropertyChangeListener 附加到工作人员，并且每当工作人员的进度值更改以及 SwingWorker 更改状态时（例如完成操作时），都会在 Swing 事件线程上通知这一点。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。有什么问题请追问。

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;
        }
    }
}