Intercepting keystrokes in plugin

[Jeff Hardin]

Hello Imagers,

I wrote a plugin a long time ago (for browsing 4d datasets from disc)  
that extends the ImageWindow class, and creates a KeyListener to act  
on the up, down, left, and right arrow keys. This worked well before  
the default behavior was to magnify or reduce the ImageWindow using  
the right and left arrow keys, as in more recent versions of ImageJ.  
Now the plugin reads the key stroke and acts on it, but the key stroke  
is passed to ImageJ, which then magnifies or reduces the ImageWindow.  
I guess I'm stupid, but I don't see how to prevent this.

Any ideas would be deeply appreciated!

Cheers,

Jeff
----------------------------------------------
Jeff Hardin
Professor and Chair, Department of Zoology
Director, Biology Core Curriculum
University of Wisconsin
1117 W. Johnson St.
Madison, WI 53706
voice: [phone]
fax: [phone]
email: [hidden email]
web page: http://worms.zoology.wisc.edu

[Joachim Wesner]

Hi Jeff,

you mean, your plugin kets the keys as it should be, but it will ALSO be
handled by ImageJ?

I´m not sure, which happens first, just did a quick internet search, there
is a

KeyEvent.consume

methods, which marks an event as already fully handled, you might give it a
try!?

Mit freundlichen Grüßen / Best regards

Joachim Wesner
Projektleiter Optik Technologiesysteme


Leica Microsystems CMS GmbH | GmbH mit Sitz in Wetzlar | Amtsgericht
Wetzlar  HRB 2432
Geschäftsführer:  Dr. Stefan Traeger | Dr. Wolf-Otto Reuter | Dr. David Roy
Martyr | Colin Davis
www.leica-microsystems.com



                                                                           
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Hello Imagers,

I wrote a plugin a long time ago (for browsing 4d datasets from disc)
that extends the ImageWindow class, and creates a KeyListener to act
on the up, down, left, and right arrow keys. This worked well before
the default behavior was to magnify or reduce the ImageWindow using
the right and left arrow keys, as in more recent versions of ImageJ.
Now the plugin reads the key stroke and acts on it, but the key stroke
is passed to ImageJ, which then magnifies or reduces the ImageWindow.
I guess I'm stupid, but I don't see how to prevent this.

Any ideas would be deeply appreciated!

Cheers,

Jeff
----------------------------------------------
Jeff Hardin
Professor and Chair, Department of Zoology
Director, Biology Core Curriculum
University of Wisconsin
1117 W. Johnson St.
Madison, WI 53706
voice: [phone]
fax: [phone]
email: [hidden email]
web page: http://worms.zoology.wisc.edu



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[dscho]

Hi,

On Wed, 22 Jul 2009, Joachim Wesner wrote:

> you mean, your plugin kets the keys as it should be, but it will ALSO be
> handled by ImageJ?
>
> I´m not sure, which happens first, just did a quick internet search, there
> is a
>
> KeyEvent.consume
>
> methods, which marks an event as already fully handled, you might give
> it a try!?

That relies on your KeyListener being called first, which is not good.

Better to removeKeyListener(IJ.getInstance()) on the ImageWindow to
prevent ImageJ from handling the keys at all.

You can then hand off the event (if it is not handled yet) to
IJ.getInstance().keyPressed().

Ciao,
Dscho

[Nico Stuurman-4]

Hi Joachim and Johannes,

>> you mean, your plugin kets the keys as it should be, but it will  
>> ALSO be
>> handled by ImageJ?

>> KeyEvent.consume
>>
>> methods, which marks an event as already fully handled, you might  
>> give
>> it a try!?
>
> That relies on your KeyListener being called first, which is not good.

Apparently, Listeners are called in reverse order of addition, which  
in this case should guarantee that the plugin's listener is called  
first.  However, propagation of the InputEvent is not stopped when the  
consume function is called, rather, a Listener should check the  
isConsumed() flag on the inputEvent and take action accordingly.  I  
had a quick look at the ImageJ code to handle KeyPresses and do not  
see the isConsumed() check there.  It seems useful to add so that  
plugin writers can use the "consume" method to signal ImageJ that they  
have handled an event.

I found the following link helpful: http://elliotth.blogspot.com/2004/08/implementing-java-listeners.html

Best,

Nico

[Wayne Rasband]

> Hello Imagers,
>
> I wrote a plugin a long time ago (for browsing 4d datasets from disc)
> that extends the ImageWindow class, and creates a KeyListener to act
> on the up, down, left, and right arrow keys. This worked well before
> the default behavior was to magnify or reduce the ImageWindow using
> the right and left arrow keys, as in more recent versions of ImageJ.
> Now the plugin reads the key stroke and acts on it, but the key stroke
> is passed to ImageJ, which then magnifies or reduces the ImageWindow.
> I guess I'm stupid, but I don't see how to prevent this.
>
> Any ideas would be deeply appreciated!

You can keep key pressed events from being passed to ImageJ by  
removing it as a KeyListener using

    removeKeyListener(IJ.getInstance());

I updated the KeyListener example plugin at

      http://rsbweb.nih.gov/ij/plugins/key-listener.html

to do this. I tried using KeyEvent.consume() but it didn't work  
because the plugin's keyPressed() method was called after ImageJ's  
keyPressed() method.

-wayne

[Jeff Hardin]

Hi folks,

Oops! I meant, of course, "... to magnify or reduce the ImageWindow  
using the up and down arrow keys..."

Cheers,

Jeff
----------------------------------------------
Jeff Hardin
Professor and Chair, Department of Zoology
Director, Biology Core Curriculum
University of Wisconsin
1117 W. Johnson St.
Madison, WI 53706
voice: [phone]
fax: [phone]
email: [hidden email]
web page: http://worms.zoology.wisc.edu



On Jul 22, 2009, at 11:00 PM, IMAGEJ automatic digest system wrote:

> Date:    Wed, 22 Jul 2009 00:39:42 -0500
> From:    Jeff Hardin <[hidden email]>
> Subject: Intercepting keystrokes in plugin
>
> Hello Imagers,
>
> I wrote a plugin a long time ago (for browsing 4d datasets from disc)
> that extends the ImageWindow class, and creates a KeyListener to act
> on the up, down, left, and right arrow keys. This worked well before
> the default behavior was to magnify or reduce the ImageWindow using
> the right and left arrow keys, as in more recent versions of ImageJ.
> Now the plugin reads the key stroke and acts on it, but the key stroke
> is passed to ImageJ, which then magnifies or reduces the ImageWindow.
> I guess I'm stupid, but I don't see how to prevent this.
>
> Any ideas would be deeply appreciated!
>
> Cheers,
>
> Jeff