How to create a KeyEvent

问题

When i create the KeyListener, it requires the following fields:

public void keyPressed(KeyEvent e) 
{

}
public void keyReleased(KeyEvent e) 
{

}
public void keyTyped(KeyEvent e) 
{

}

When i put System.out.println(e) into the keyPressed method, though, it returns this when i press the enter key:

java.awt.event.KeyEvent[KEY_PRESSED,keyCode=10,keyText=?,keyChar=?,keyLocation=KEY_LOCATION_STANDARD,rawCode=0,primaryLevelUnicode=0,scancode=0] on javax.swing.JButton[,1,1,100x100,alignmentX=0.0,alignmentY=0.5,border=com.apple.laf.AquaButtonBorder$Dynamic@13b33a0e,flags=288,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=0,left=2,bottom=0,right=2],paintBorder=true,paintFocus=true,pressedIcon=,rolloverEnabled=false,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=HI,defaultCapable=true]

This is obviously not a KeyEvent, so I cannot use it to call the keyPressed(KeyEvent e). What I want to be able to do is simulate the pressing of a key, specifically the enter key, in a way that would activate the keyListener and would output that text into a JTextArea.

Note: I looked at the accepted answer for How can I perfectly simulate KeyEvents?, and understood little of how it actually works, and i want code i understand. I also looked here How to simulate keyboard presses in java?, but not i could not get the robot to work; nothing happened when a key was supposed to be pressed.

回答1:

e is the KeyEvent.

if you want to see the e value, then you can try this

System.out.println(e.getKeyChar());

Creating KeyEvent :

KeyEvent e = new KeyEvent(Component source, int id, long when, int modifiers, int keyCode, char keyChar, int keyLocation);

Example (dunno if this is the right way, but it produce the right output):

Button a = new Button("click");
    KeyEvent e;
    e = new KeyEvent(a, 1, 20, 1, 10, 'a');
    System.out.println(""+e.getKeyChar());
    System.out.println(""+e.getKeyCode());

Here is the all type of KeyEvent parameters

java.awt.event.KeyEvent
@Deprecated public KeyEvent(Component source, int id, long when, int modifiers, int keyCode)
Deprecated. as of JDK1.1

===

java.awt.event.KeyEvent
public KeyEvent(Component source, int id, long when, int modifiers, int keyCode, char keyChar)
Constructs a KeyEvent object.
Note that passing in an invalid id results in unspecified behavior. This method throws an IllegalArgumentException if source is null.
Parameters:
source - the Component that originated the event id - an integer identifying the type of event when - a long integer that specifies the time the event occurred modifiers - the modifier keys down during event (shift, ctrl, alt, meta) Either extended _DOWN_MASK or old _MASK modifiers should be used, but both models should not be mixed in one event. Use of the extended modifiers is preferred. keyCode - the integer code for an actual key, or VK_UNDEFINED (for a key-typed event) keyChar - the Unicode character generated by this event, or CHAR_UNDEFINED (for key-pressed and key-released events which do not map to a valid Unicode character) 
Throws:
IllegalArgumentException - if id is KEY_TYPED and keyChar is CHAR_UNDEFINED; or if id is KEY_TYPED and keyCode is not VK_UNDEFINED IllegalArgumentException - if source is null

===

java.awt.event.KeyEvent
public KeyEvent(Component source, int id, long when, int modifiers, int keyCode, char keyChar, int keyLocation)

回答2:

When using robot, first obtain focus of component to which you add your KeyListener to. Then you can use robot to simulte key presses. As an alternative, you can just use dispatchEvent on component to which your listener is added.

KeyEvent key = new KeyEvent(inputField, KeyEvent.KEY_TYPED, System.currentTimeMillis(), 0, KeyEvent.VK_UNDEFINED, 'Z');
inputField.dispatchEvent(key);

Providing you have:

JInputField InputField = new JInputField();

You can as well create KeyEvent as described above and pass it to keyTyped method of your listener. As for keyPrssed, you can do the same.

回答3:

You state:

I believe it would make part of my code more efficient. When certain conditions are met (I am doing hang man, and this is a "cheat" that is a joke with my teacher) the computer will press the correct keys to "guess" the answer. and then there is the simple, i wonder if i can? part of it. that got started when i saw JButton.doClick() and wondered if it had one for JTextFields

As I suspected, you are going about this all wrong. If you want your program to press keys for you, there's no need to create KeyEvents. If the "keys" are JButtons, then simply calling doClick() on the button will do. If you are desiring to fill text into a JTextField, then simply setting the text is all that is needed. i.e.,

For instance if you called the bit of text below in a Swing Timer (to slow it down so that you see the text being added:

String myText = myTextField.getText();
myText += nextBitOfText;
myTextField.setText(myText);

You would likely get the effect you desire.

For example:

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;

import javax.swing.*;

@SuppressWarnings("serial")
public class AddTextToTextField extends JPanel {
   public static final String[] POSSIBLE_TEXTS = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday"};
   public static final int TIMER_DELAY = 500;
   private JTextField myTextField = new JTextField(20);
   private JButton myButton = new JButton(new BtnAction("Press Me"));
   private Random random = new Random();

   public AddTextToTextField() {
      add(myTextField);
      add(myButton);
   }

   private class BtnAction extends AbstractAction {
      public BtnAction(String text) {
         super(text);
      }

      @Override
      public void actionPerformed(ActionEvent arg0) {
         setEnabled(false);
         myTextField.setText("");
         myTextField.setFocusable(false);
         String randomText = POSSIBLE_TEXTS[random.nextInt(POSSIBLE_TEXTS.length)];
         new Timer(TIMER_DELAY, new TimerAction(this, randomText)).start();
      }
   }

   private class TimerAction implements ActionListener {
      private AbstractAction btnAction;
      private String text;
      private int count = 0;

      public TimerAction(AbstractAction btnAction, String text) {
         this.btnAction = btnAction;
         this.text = text;
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         if (count <= text.length()) {
            myTextField.setText(text.substring(0, count));
            count++;
         } else {
            ((Timer)e.getSource()).stop();
            btnAction.setEnabled(true);
            myTextField.setFocusable(true);
         }
      }
   }

   private static void createAndShowGui() {
      AddTextToTextField mainPanel = new AddTextToTextField();

      JFrame frame = new JFrame("AddTextToTextField");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

回答4:

You can use this to dispatch a virtual event:

textArea.dispatchEvent(new KeyEvent(jFrame,
        KeyEvent.KEY_TYPED, System.currentTimeMillis(),
        0,
        KeyEvent.VK_ENTER));

Try that out, it should work but that was from memory

来源：https://stackoverflow.com/questions/14867040/how-to-create-a-keyevent

标签

java

jtextfield

keylistener

keyevent