java - 为什么我的线程在 Swing 中不能正常工作？

Question

我正在使用简单的 for 循环打印简单值以附加 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...

但是如果我在文本区域附加 JTextArea 和打印值，它们将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);
            }
        }
    });
}
}

想一个一个追加，结果是整个程序运行完才追加

Answer 1

您的问题在于您对 Thread.sleep 的使用，因为当您在 Swing 事件线程(或事件调度线程的 EDT)上调用它时，它将把整个 Swing事件线程 hibernate 。当这种情况发生时，该线程的操作将无法执行，包括绘制 GUI(更新它)和与用户交互，这将完全卡住您的 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，因为我们不想附加到此线程之外的 JTextArea。

此外，正如其他人所指出的，如果您只想在 Swing 中延迟执行重复操作，那么是的，请使用此 Swing 计时器。另一方面，如果您希望在 Swing 中运行一段长时间运行的代码，那么这段代码将再次阻止 EDT 并卡住您的程序。对于这种情况，请使用后台线程，例如 SwingWorker 提供的线程。请查看 Lesson: Concurrency in Swing有关更多信息。

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();
    }
});

整个事情:

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，这里是上面同一程序的示例，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，只使用一个 while 循环将计数器变量推进一个有界的随机数。然后它传输使用这个值来更新它自己的进度属性(一个只能从 0 到 100 的值，因此在其他情况下，该值将需要被规范化以符合这个)。我将一个 PropertyChangeListener 附加到 worker，每当 worker 的进度值发生变化以及 SwingWorker 更改状态(例如完成操作)时，它都会在 Swing 事件线程上 收到通知。在后一种情况下，worker 的 StateValue 变为 StateValue.DONE。监听器然后相应地更新 GUI。有问题请追问。

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;
        }
    }
}