Post a KeyEvent to the focused component

Question

What is the best way to post a Button Press to a component? I tried using the Robot class and it works, normally. However, this class has some problems under some Linux platforms, so I wonder what is the best Java-only way to post an event to a component.

In this particular case, I want to post backspace events to a JTextField when I press a button.

EDIT: I've used the Robot class after all. I fixed the problem that prevented this class from working correctly under Linux

Answer 1

There's also this approach to avoid relaying in the robot:

import java.awt.*;
import java.awt.event.KeyEvent;
import javax.swing.*;

public class KeyEventTest
{
    public static void main(String[] args)
    {
        final JTextField textField = new JTextField(8);
        textField.setFont(textField.getFont().deriveFont(18f));
        JPanel panel = new JPanel(new GridBagLayout());
        panel.add(textField, new GridBagConstraints());
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(panel);
        f.setSize(300,160);
        f.setLocation(200,200);
        f.setVisible(true);
        new Thread(new Runnable()
        {
            public void run()
            {
                Toolkit toolkit = Toolkit.getDefaultToolkit();
                EventQueue queue = toolkit.getSystemEventQueue();
                try {
                    Thread.sleep(1500);
                } catch(InterruptedException ie) { }
                char newChar = 'x';
                queue.postEvent(new KeyEvent(textField,
                                             KeyEvent.KEY_TYPED,
                                             System.currentTimeMillis(),
                                             0,
                                             KeyEvent.VK_UNDEFINED,
                                             newChar));
                try {
                    Thread.sleep(1500);
                } catch(InterruptedException ie) { }
                queue.postEvent(new KeyEvent(textField,
                                             KeyEvent.KEY_PRESSED,
                                             System.currentTimeMillis(),
                                             0,
                                             KeyEvent.VK_BACK_SPACE,
                                             KeyEvent.CHAR_UNDEFINED));
            }
        }).start();
    }
}

I must warn you that if the component loses the focus the generated events will be lost! D:

Answer 2

I ended up using the robot class, which was the easiest way after all. The problem is that in the specific Linux distro I was using, the instantiation of the Robot class would hang the Virtual Machine. Looking at the log files I found out that java was trying to load a DLL that wasn't available:

libXi.so.6

After adding this library to the distro I was able to continue

Answer 3

You can find example of such key post event, like in this class

Those posts are using the dispatchEvent() function

public void mousePressed(MouseEvent event) {
    KeyboardButton key = getKey(event.getX(), event.getY());

[...]

      KeyEvent ke;
      Component source = Component.getFocusComponent();
      lastPressed = key;
      lastSource = source;
      key.setPressed(true);

      if(source != null) {

        if((key == k_accent || key == k_circle) && (lastKey instanceof KeyboardButtonTextJapanese)) {
          int accent = ((KeyboardButtonTextJapanese)lastKey).getAccent();
          if(accent >= 1 && key == k_accent) {

            /*
            ** First send a backspace to delete the previous character, then send the character with the accent.
            */

            source.dispatchEvent(new KeyEvent(source, KeyEvent.KEY_PRESSED, System.currentTimeMillis(), 0, k_backspace.getKeyEvent(), k_backspace.getKeyChar()));
            source.dispatchEvent(new KeyEvent(source, KeyEvent.KEY_TYPED,   System.currentTimeMillis(), 0, k_backspace.getKeyEvent(), k_backspace.getKeyChar()));