java - doInBackground 不起作用

Question

我创建了一个小型 BackGroundWorker 来测试 pdf 文件。一切正常，直到代码捕获 pdf 文件的路径。我真的不知道为什么它不起作用 -.- 我也没有在 Eclipse 的控制台中收到任何错误消息。你知道我的问题到底是什么吗？

public class SwingWorkerDemo {
    static JButton pressMe;
    static JPanel buttonPanel;
    static String text;
    protected static JTextArea textArea = new JTextArea(25, 45);

    public SwingWorkerDemo() {
        JFrame frame = new JFrame();
        frame.setVisible(true);

        buttonPanel = new JPanel();
        buttonPanel.setLayout(new FlowLayout(FlowLayout.RIGHT));
        pressMe= new JButton("Drück mich");
        buttonPanel.add(pressMe);
        frame.add(buttonPanel);
        frame.pack();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        pressMe.addActionListener(new java.awt.event.ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                try {
                    runWorker();
                } catch (PDFDocumentException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }
            }
        });
    }

    static class MyTask extends SwingWorker<Void, Void> {

        public MyTask() throws PDFDocumentException {
            JFrame frame = new JFrame();
            frame.setVisible(true);

            frame.add(textArea);
            frame.pack();
        }

        @SuppressWarnings("resource")
        @Override
        protected Void doInBackground() throws Exception {
            File inputFiles = new File("C:\\Users\\Tommy\\Desktop\\pdf\\Name_der_testenden.pdf");
            PDFDocument pdf = new PDFDocument(inputFiles);

            textArea.setText("content errors:" + "\n");
            for (int pageNo = 1; pageNo < pdf.getPages(); pageNo++) {
                try {
                    PCProperty content = pdf.getContent(pageNo, ContentCollationOptions.NONE);

                    if (content == null) {
                       textArea.setText("no content on page " + pageNo + "\n");
                    }

                } catch (PDFDocumentException exception) {
                    textArea.setText("failed to read content on page " + pageNo + "\n");
               }
            }
            return null;
        }
    }

 public static void runWorker() throws PDFDocumentException {

        MyTask task = new MyTask();
        task.execute();
    }

    public static void main(String[] args) throws PDFDocumentException {
        new SwingWorkerDemo();
        }
}

Answer 1

我不是专家，但我稍微改变了你的代码。首先，我在调用 execute() 之前为工作人员创建了窗口，我通过构造函数将 textArea 传递给任务，并在那里使用 process( ) 方法来更新它。

这是代码，注意:我只是使用了一些带有 Thread.sleep() 的字符串来模拟进度。

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.List;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.SwingWorker;

public class SwingWorkerDemo 
{
    static JButton pressMe;
    static JPanel buttonPanel;
    static String text;
    protected static JTextArea textArea = new JTextArea(25, 45);

    public SwingWorkerDemo() {
        JFrame frame = new JFrame("Main Frame");
        frame.setVisible(true);

        buttonPanel = new JPanel();
        buttonPanel.setLayout(new FlowLayout(FlowLayout.RIGHT));
        pressMe= new JButton("Drück mich");
        buttonPanel.add(pressMe);
        frame.add(buttonPanel);
        frame.pack();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        pressMe.addActionListener(new ActionListener()
        {
            @Override
            public void actionPerformed(ActionEvent arg0) 
            {
                JFrame frame = new JFrame("Worker Frame");
                frame.setVisible(true);

                frame.add(textArea);
                frame.pack();

                MyTask task = new MyTask(textArea);
                task.execute();
            }
        });
    }

    static class MyTask extends SwingWorker<String, String> 
    {
        private JTextArea innerTextArea;

        public MyTask(JTextArea innerTextArea)
        {
            this.innerTextArea = innerTextArea;
        }

        @Override
        protected String doInBackground() throws Exception 
        {
            publish("First message:" + "\n");
            Thread.sleep(2000);
            publish(" no content on page 2:" + "\n");
            Thread.sleep(2000);
            publish(" no content on page 4:" + "\n");
            Thread.sleep(2000);
            publish(" no content on page 5" + "\n");
            Thread.sleep(2000);

            return "reading done";
        }

        @Override
        protected void process(List<String> chunks)
        {
            innerTextArea.append(chunks.get(chunks.size() - 1));
        }

        @Override
        public void done() 
        {
            try 
            {
               innerTextArea.append(get());
            } 
            catch (Exception e)
            {
               e.printStackTrace(System.err);
               System.out.println("error");
            }
        }

    }



    public static void main(String[] args)
    {
        new SwingWorkerDemo();
    }
}

有关更多信息，请查看 documentation SwingWorker 的。