Is KeyListenening wothout focus possible?

General Discussions
#1

Note: Ive earlier been critizised for not posting in the right forum, but I really have no clue where else to post this one:

Question: I would like to hear if it is possible to get notified when a key is pressed even though my program doesnt have focus?

Reason for posting: Im working on a robot that hopefully one day will be able to play poker on my command when I scream into my microphone lying on my bed like a lazy donkey :slight_smile:

#2

I believe you can add an AWTEventListener directly to the awt event queue by using.

java.awt.Toolkit - addAWTEventListener.

You’ll have to convert the events back into KeyEvents (just a cast on the right event code).

Kev

#3

Hmmm I have got this far as to create the AWTEventListener:


AWTEventListener l = new AWTEventListener() {
            public void eventDispatched(AWTEvent arg0) {
                  //Here I will place my actions
            }
      };

But where do you mean I should add it?

#4 

AWTEventListener listener = 
          new AWTEventListener() {
            public void eventDispatched(AWTEvent event) {
              KeyEvent ke = (KeyEvent)event;
              if (ke.getID() == KeyEvent.KEY_TYPED) {
                buffer.append(ke.getKeyChar());
            }
          }
        };
        Toolkit toolkit = Toolkit.getDefaultToolkit();
        toolkit.addAWTEventListener(
          listener, AWTEvent.KEY_EVENT_MASK);

http://java.sun.com/developer/JDCTechTips/2003/tt0624.html

Kev

#5 
public class A {
      public static void main(String[] args) {
            AWTEventListener l = new AWTEventListener() {
                  public void eventDispatched(AWTEvent arg0) {
                        System.out.println(System.out.println());
                  }
            };
            Toolkit toolkit = Toolkit.getDefaultToolkit(); 
            toolkit.addAWTEventListener(l, AWTEvent.KEY_EVENT_MASK); 
      }

}

This code gives me this error message:

[quote]Exception in thread “main” java.lang.VerifyError: (class: main/A$1, method: eventDispatched signature: (Ljava/awt/AWTEvent;)V) Unable to pop operand off an empty stack
at main.A.main(A.java:53)
[/quote]
Do you have any clue whats wrong?

#6

Did you compile with one version of java then run with another? Normally where VerifyErrors turn up.

Kev

#7

I made some copy pasting from the url you sent me. Now I get no error message but I dont see anything happen when typing a key:

public class A {
    public static void main(String args[]) {
        AWTEventListener listener = 
          new AWTEventListener() {
            public void eventDispatched(AWTEvent event) {
              KeyEvent ke = (KeyEvent)event;
              if (ke.getID() == KeyEvent.KEY_TYPED) {
                System.out.println("Key typed");
            }
          }
        };
        Toolkit toolkit = Toolkit.getDefaultToolkit();
        toolkit.addAWTEventListener(
          listener, AWTEvent.KEY_EVENT_MASK);
      }

}
#8

Ah ha, I think you actually do need to create a component… maybe not show it… but AWT needs to get initiallised to start the event queueing.

At least I think so,

Kev

#9

that means if I add the Listener inside a class extending a Frame is should work?

#10

I’d think so, I take it, it doesn’t?

Kev

#11

Well it works while the Frame is visible but it I dont use setVisible(true) og if I use hide(); after setting visibility to true then it doesnt react on anymore.

It seems that the solution only works when the Component they are attached to is in focus.

I was searching for some kind of listener that would be able to react on key pressings even though the program is in the background. Do you have any other suggestions?

#12

JInput might solve what you want? Though I think that may have a similar restriction.

If the application is in the background (i.e. not even the focus from a dos/shell window) then any event driven system will fail. You might be getting to the point where you’ll need to be making O/S specific calls to monitor key input.

Kev

#13

I will go read about JInput and see what that could do. Thanks again. Especially for the fast replies :slight_smile:

#14

Do you know if it would be possible to use that awtlistener with mouseMove detection too? in that case, how?

#15

Just need to modify the mask:



   toolkit.addAWTEventListener( 
     listener, AWTEvent.KEY_EVENT_MASK | AWTEvent.MOUSE_MOTION_EVENT_MASK);

or summink…

Kev

#16

[quote]Note: Ive earlier been critizised for not posting in the right forum, but I really have no clue where else to post this one:
[/quote]
If you’re really not sure, and it’s a question about java core libraries, Clueless Newbies is a good bet. Especially since a lot of people read that with the intent of answering questions ;D

#17

There is a new class added in 1.5 called java.awt.MouseInfo that I have been playing with. It allows you to get the system wide mouse coordinates without opening a window or anything. Unfortunately it is awkward to use and there is no way to poll the mouse buttons, but it is nice to have.

I think polling the keyboard outside of a focused window is still something you cannot do without an external library.

I assume you know about the java.awt.Robot class that you can use to generate keypresses and move the mouse with since you mentioned “Robot” above.