计算时在 JTextArea 中显示文本 [英] Showing text in JTextArea while calculating

问题描述

我正在编写的一个应用程序包括一个 JButton 和一个 JTextArea.单击按钮会导致长时间计算，从而导致在 JTextArea 中显示文本.即使计算很长，我也可以在旅途中得到中间结果(例如，考虑一个将 pi 近似为 100 位的应用程序 - 每隔几秒我就可以写另一个数字).问题是，即使我编写(在 ActionListener 类中，因为按钮调用了计算)将 JTextArea 的文本设置为某些东西，在计算完成时它也不会显示，我只能看到结尾结果，计算结束后.

An application I am writing consists, among others, a JButton and a JTextArea. A click on the button leads to a long calculation, resulting in a text shown in the JTextArea. Even though the calculation is long, I can have middle-results on the go (think, for example, of an application which approximates pi up to 100 digits - every few seconds I could write another digit). The problem is, that even if I write (being in the ActionListener class because the button invoked the calculation) to set the text of the JTextArea to something, it isn't shown while the calculation is done, and I can only see the end result, after the calculation is over.

为什么会这样，我该如何解决?

Why is it so, and how can I fix it?

提前谢谢你.

推荐答案

您的问题是您在主 Swing 线程(EDT)中进行了长时间计算，这将冻结您的整个 GUI，直到进程自行完成.一种解决方案是使用后台线程进行计算，并且一种简单的方法是使用 SwingWorker 为主 Swing 线程、EDT 创建线程背景，并将中间结果发布/处理到 JTextArea 中.有关 SwingWorkers 和 EDT 的更多信息，请查看此处:Swing 中的并发

Your problem is that you're doing a long calculation in the main Swing thread, the EDT, and this will freeze your entire GUI until the process has completed itself. A solution is to use a background thread for your calculation, and an easy way to do this it to use a SwingWorker to create a thread background to the main Swing thread, the EDT, and publish/process the interim results into the JTextArea. For more on SwingWorkers and the EDT, please look here: Concurrency in Swing

另外，如果您提供一个体面的sscce，我们甚至可以提供更详细的回复，甚至可能提供示例代码.

Also, if you provide a decent sscce we can probably give you a more detailed response perhaps even with sample code.

SSCCE 示例:

import java.awt.event.*;
import java.text.DecimalFormat;
import java.util.List;
import javax.swing.*;

public class InterimCalc {
   private JPanel mainPanel = new JPanel();
   private JTextField resultField = new JTextField(10);
   private JButton doItBtn = new JButton("Do It!");
   private DecimalFormat dblFormat = new DecimalFormat("0.0000000000");
   private SwingWorker<Void, Double> mySwingWorker = null;

   public InterimCalc() {
      mainPanel.add(doItBtn);
      mainPanel.add(resultField);
      displayResult(0.0);

      doItBtn.addActionListener(new DoItListener());
   }

   public void displayResult(double result) {
      resultField.setText(dblFormat.format(result));
   }

   public JPanel getMainPanel() {
      return mainPanel;
   }

   private class DoItListener implements ActionListener {

      public void actionPerformed(ActionEvent e) {
         if (mySwingWorker != null && !mySwingWorker.isDone()) {
            mySwingWorker.cancel(true);
         }
         displayResult(0.0);
         mySwingWorker = new MySwingWorker();
         mySwingWorker.execute();
      }
   }

   private class MySwingWorker extends SwingWorker<Void, Double> {

      private static final int INTERIM_LENGTH = 10000; // how many loops to do before displaying

      @Override
      protected Void doInBackground() throws Exception {
         boolean keepGoing = true;
         long index = 1L;
         double value = 0.0;
         while (keepGoing) {
            for (int i = 0; i < INTERIM_LENGTH; i++) {
               int multiplier = (index % 2 == 0) ? -1 : 1;
               value += (double)multiplier / (index);
               index++;
            }
            publish(value);
         }
         return null;
      }

      @Override
      protected void process(List<Double> chunks) {
         for (Double dbl : chunks) {
            displayResult(dbl);
         }
      }

   }

   private static void createAndShowUI() {
      JFrame frame = new JFrame("Decay Const");
      frame.getContentPane().add(new InterimCalc().getMainPanel());
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      java.awt.EventQueue.invokeLater(new Runnable() {
         public void run() {
            createAndShowUI();
         }
      });
   }
}

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