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Can't catch CTRL-C if the user releases the keys in the wrong order. [message #869688]

Thu, 03 May 2012 20:36

Dave Dell

Messages: 8
Registered: April 2012

Junior Member

We have an application using SWT widgets. We'd like to do some processing when a user clicks CTRL-C when one of the widgets has focus. We added a KeyListener to the object, and in the keyReleased() method we checked for CTRL-C this way:

if ((ev.stateMask == 0x40000) && (ev.keyCode == 67))

. Depending on the order the user released the keys, the stateMask is either 0 or has the value for CTRL. If the user released the CTRL key first, the stateMask is 0; if the user released the C key first, the stateMask has the value for CTRL. So sometimes our code gets processed, and sometimes it doesn't. Is that what should happen? Is there anyway to process this as CTRL-C regardless of which key is released first? Thanks.

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Re: Can't catch CTRL-C if the user releases the keys in the wrong order. [message #870515 is a reply to message #869688]

Tue, 08 May 2012 13:52

Grant Gayed

Messages: 2150
Registered: July 2009

Senior Member

Listeners like this are usually hooked on KeyPressed rather than
KeyReleased. If you change to this then you'll likely find that users
won't make the mistake you're describing, as I can't imagine going to
press Ctrl+C and pressing the 'C' first.

Grant

On 5/3/2012 4:36 PM, Dave Dell wrote:
> We have an application using SWT widgets. We'd like to do some
> processing when a user clicks CTRL-C when one of the widgets has focus.
> We added a KeyListener to the object, and in the keyReleased() method we
> checked for CTRL-C this way: if ((ev.stateMask == 0x40000) &&
> (ev.keyCode == 67)). Depending on the order the user released the keys,
> the stateMask is either 0 or has the value for CTRL. If the user
> released the CTRL key first, the stateMask is 0; if the user released
> the C key first, the stateMask has the value for CTRL. So sometimes our
> code gets processed, and sometimes it doesn't. Is that what should
> happen? Is there anyway to process this as CTRL-C regardless of which
> key is released first? Thanks.

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Re: Can't catch CTRL-C if the user releases the keys in the wrong order. [message #870568 is a reply to message #870515]

Tue, 08 May 2012 19:01

Dave Dell

Messages: 8
Registered: April 2012

Junior Member

Well, interestingly enough, today I just tried to catch it using keyPressed(), but it didn't work. What I discovered is that if you have the CTRL key pressed, the keyPressed() method never gets called, even when pressing the "c". I also learned that the Windows OS doesn't copy to the clipboard if you press "c" and then CTRL. So what I did was set a flag in keyPressed() when called to indicate that an invalid copy key sequence was pressed, because the only time it will get called is when a key is pressed by itself (not with a CTRL key). I then checked that flag in the keyReleased() method. If the flag hadn't been set by keyPressed() and the key pressed was a "c" then I assumed the user just released CTRL-C (in any order) and do the processing that needs to be done in that case.

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