在迭代中更新textArea

Question

i have a fun project where i need to change the content of a text area inside a iteration.

Its a character, a "projectile", moving trought a string. The string is updated and sent to the textArea inside the iteration, and the iteration stops when the character reaches a wall.

But my textArea only updates (visually) when i leave the iteration. While im inside it, textArea freezes, as if its waiting for the iteration, even with Thread.sleep() inside it.

I made an MVCE exemplifing the problem bellow, notice the text only shows after the iteration, i want it to apper in every step of the while.

public class GUIProblem extends JFrame{
    public GUIProblem() {
        setSize(640, 480);

        JPanel panel = new JPanel();
        getContentPane().add(panel, BorderLayout.CENTER);

        final JTextArea textArea = new JTextArea();
        textArea.setRows(10);
        textArea.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent arg0) {
                int i = 0;
                while(i < 10){
                    textArea.setText("this text only appears after the iteration, i want it to appear in each step of the iteration!");
                    System.out.println("iterating..." + i++);
                    try {
                        Thread.sleep(200);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        });
        textArea.setColumns(30);
        panel.add(textArea);
    }

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                GUIProblem gui = new GUIProblem( );
                gui.setVisible(true);
            }
        });
        JOptionPane.showMessageDialog(null, "Click the textArea!");
    }   
}

Answer 1

You've a classic Swing threading issue where you stop the Swing event thread in its tracks with your iteration and its Thread.sleep() calls. The solution is the same as for similar questions: use a Swing Timer or background thread such as a SwingWorker. In your case, use the Timer.

For example, since you posted an MCVE

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;

public class GUIProblem extends JFrame {
   public GUIProblem() {
      // setSize(640, 480);

      JPanel panel = new JPanel();
      getContentPane().add(panel, BorderLayout.CENTER);

      final JTextArea textArea = new JTextArea(20, 50);
      textArea.addMouseListener(new MouseAdapter() {
         @Override
         public void mouseClicked(MouseEvent mEvt) {
            int i = 0;
            int timerDelay = 200;
            new Timer(timerDelay, new ActionListener() {
               int count = 0;
               private final int MAX_COUNT = 10;
               @Override
               public void actionPerformed(ActionEvent e) {
                  if (count >= MAX_COUNT) {
                     ((Timer) e.getSource()).stop(); // stop the timer
                     return;
                  }
                  textArea.append("Count is: " + count + "\n");
                  count++;
               }
            }).start();
         }
      });

      panel.add(new JScrollPane(textArea));
   }

   /**
    * 
    */
   private static final long serialVersionUID = 1L;

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         @Override
         public void run() {
            GUIProblem gui = new GUIProblem();
            gui.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
            gui.pack();
            gui.setLocationRelativeTo(null);
            gui.setVisible(true);
         }
      });
      JOptionPane.showMessageDialog(null, "Click the textArea!");
   }
}