RE: [Flashcoders] How to detect for modifier (alt/ctrl) keys

[Benny]

Hi Glen,

I tried your code (somewhat modified, see below, to get the desired traces)
but it gives me the same result. 
E.g. if I hit (right) Alt-5 it traces:

onKeyDown: _ctrlKeyDown=true, _altKeyDown=false, keyCode=17
onKeyDown: _ctrlKeyDown=true, _altKeyDown=true, keyCode=18
onKeyDown: _ctrlKeyDown=true, _altKeyDown=true, keyCode=53
onKeyUp: _ctrlKeyDown=true, _altKeyDown=true, keyCode=53
onKeyUp: _ctrlKeyDown=true, _altKeyDown=false, keyCode=18

Notice that the KEY_DOWN event fires twice for the right alt key!
 
If I just press and release the right alt key it traces:

onKeyDown: _ctrlKeyDown=true, _altKeyDown=false, keyCode=17
onKeyDown: _ctrlKeyDown=true, _altKeyDown=true, keyCode=18
onKeyUp: _ctrlKeyDown=true, _altKeyDown=false, keyCode=18 

So the first trace shows a phantom control key press ...

This lead me to the following work-around (Flash Pro script):

import flash.events.KeyboardEvent;
import flash.ui.Keyboard;

stage.addEventListener(KeyboardEvent.KEY_DOWN, onKeyDownOrUpHandler);
stage.addEventListener(KeyboardEvent.KEY_UP, onKeyDownOrUpHandler);

var _ctrlKeyDown:Boolean;
var _altKeyDown:Boolean;

function onKeyDownOrUpHandler(e:KeyboardEvent):void
{       
        if (e.keyCode==17 || e.keyCode==18) // then always test both Ctrl
and Alt to work around possible bug:
        {
                _ctrlKeyDown = e.keyCode == Keyboard.CONTROL;
                _altKeyDown = e.keyCode == Keyboard.ALTERNATE;
        }
        trace(e.type + ": _ctrlKeyDown=" + _ctrlKeyDown + ", _altKeyDown=" +
_altKeyDown + ", character: " + String.fromCharCode(e.charCode));       
}

So the trick is to flag both ctrlKeyIsDown and _altKeyIsDown every time.
This will override the phantom event.

It would be great if you and/or anybody else could confirm the initial bogus
key down event for the right alt key on press. 
I tested this so far on two systems with MS Vista and tested with various
debug 10 and 10.1 players, stand alone and in browser. In all cases I got
the bogus control event when pressing alt.

If this is a bug I will log it to Adobe's bug base with the discovered
work-around.

Thanks!

- Benny


By the way this is how I modified your code to get the traces I want (in
Flash Pro):

import flash.events.KeyboardEvent;

const CTRL_KEYCODE:int = 17;
const ALT_KEYCODE:int = 18;

var _ctrlKeyDown:Boolean = false;
var _altKeyDown:Boolean = false;

stage.addEventListener(KeyboardEvent.KEY_DOWN, onKeyDownHandler);
stage.addEventListener(KeyboardEvent.KEY_UP, onKeyUpHandler);

function onKeyDownHandler(e:KeyboardEvent):void
{
        switch(e.keyCode) {

                case CTRL_KEYCODE:
                        _ctrlKeyDown = true;                    
                        break;
                case ALT_KEYCODE:
                        _altKeyDown = true;                             
                        break;
        }
        
        trace("onKeyDown: _ctrlKeyDown=" + _ctrlKeyDown + ", _altKeyDown=" +
_altKeyDown + ", keyCode="+e.keyCode);

}

function onKeyUpHandler(e:KeyboardEvent):void
{
        switch(e.keyCode) {

                case CTRL_KEYCODE:
                        _ctrlKeyDown = false;
                        break; //your choice if you put break after return
                case ALT_KEYCODE:
                        _altKeyDown = false;                            
                        break;
        }

        trace("onKeyUp: _ctrlKeyDown=" + _ctrlKeyDown + ", _altKeyDown=" +
_altKeyDown + ", keyCode="+e.keyCode);

}


-----Oorspronkelijk bericht-----
Van: flashcoders-boun...@chattyfig.figleaf.com
[mailto:flashcoders-boun...@chattyfig.figleaf.com] Namens Glen Pike
Verzonden: dinsdag 16 november 2010 1:08
Aan: Flash Coders List
Onderwerp: Re: [Flashcoders] How to detect for modifier (alt/ctrl) keys

Yes, but if you don't use keyEvent.ctrlKey in your event handler, but 
check for CTRL and set a flag:

e.g.

public static const CTRL_KEYCODE:int = 17;
private var _ctrlKeyDown:Boolean = false;
//etc

function onKeyDownHandler(e:KeyboardEvent):void
{
        switch(e.keyCode) {

                case CTRL_KEYCODE:
                        _ctrlKeyDown = true;
                        return;
                        break; //your choice if you put break after return
                //case ALT_KEYCODE:
                //      _altKeyDown = true;     
                //      return;
                //      break;
                default:
                        break;
        }
        
        trace("onKeyDown: ctrlKeyDown=" + _ctrlKeyDown);

}

function onKeyUpHandler(e:KeyboardEvent):void
{
        switch(e.keyCode) {

                case CTRL_KEYCODE:
                        _ctrlKeyDown = false;
                        return;
                        break; //your choice if you put break after return
                //case ALT_KEYCODE:
                //      _altKeyDown = false;    
                /       return;
                //      break;
                default:
                        break;
        }

        trace("onKeyUp: e.ctrlKey=" + e.ctrlKey + ", e.altKey=" + e.altKey);

}


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