OS X Mouse Wheel Support for Flex 2 Applications

Filed under ActionScript 3, Flex, Mac, Programming
Note: This version of this solution is deprecated. I've made a separate post about the new version, which you can find here.

In my current job I have been programming user interfaces for applications that display networks of data (as in nodes, links etc.) with the Adobe Flex framework, and the UI paradigm I have been utilizing is a kind of a Zoomable User Interface (ZUI). The idea there is to enable the user to view and manipulate objects on a two-dimensional plane, and navigate around that plane by zooming and panning.

Now, the easiest way (at least for me) to control the zooming is to use the mouse wheel. Mouse wheel support for Flex is implemented by registering an event listener of type MouseEvent.MOUSE_WHEEL with the DisplayObject that would dispatch the event. Sadly, mouse wheel support is not available in the Mac OS X version of Flash Player. This prompted me to create a custom solution, as my main computer is a MacBook and I would like to be able to test the mouse wheel navigation with my development machine.

Update: The javascript now works with more browsers than just Firefox 2 and Safari 2. I Tested it, in addition to those two, with Opera 9, Camino 1.5 and Omniweb 5.5, and it seems to work in all of them now.

Update #2: Changed the javascript code to also work with Safari 3 beta. When using it, small movements with the wheel do not invoke any action, so you'll have to roll it a bit further to make the app respond.

Update #3: Added statement about licensing the code under the MIT License as per request of Philip Flip Kromer

Update #4 (feb 8, 08): If you're looking for AS3 (not Flex) OS X mouse wheel support, check out PixelBreaker.com.

Update #5 (feb 12, 08): Fljot sent me a version of this that works also in non-Flex AS3 projects. He also fixed some issues in the code related to the automatic registration of listening objects. You can find him here.

The solution has been tested with Firefox 2 and Safari 2 Firefox 2, Safari 2, Opera 9, Camino 1.5 and Omniweb 5.5, and it is based on two main elements:


Just include the osxmousewheel.js file in your HTML and specify the ids/names of your flash object element and the div element that contains the flash object:

<script type="text/javascript"> 
    var mw_flashMovieId = "flashMovie"; // the id/name of your flash app's HTML DOM element  	
    var mw_flashContainerId = "flashContainerDiv"; // the id/name of the flash element's surrounding div element  
<script src="./osxmousewheel.js" type="text/javascript"></script>


The singleton has to be created first, and that can be done by getting a reference to the instance property in at least one place:

import org.hasseg.externalMouseWheel.*;
private var _mwSupport:ExternalMouseWheelSupport = ExternalMouseWheelSupport.instance;

Then, all objects that you want to have the OS X mouse wheel support enabled for have to be registered with the ExternalMouseWheelSupport class. This can be done in two ways:

  1. Manually:
  2. This is the more foolproof way. First make sure that the registerAutomatically property is set to false (it is true by default):
    ExternalMouseWheelSupport.registerAutomatically = false;

    Then just register the objects one by one:


    or several at a time:

    _mwSupport.registerObjects([myBox, myButton, mySlider]);
  3. Automatically:
  4. This is the easier, but more bug-prone way. Simply make sure that the registerAutomatically property is set to true (it is true by default, so you actually don't even need to do this):
    ExternalMouseWheelSupport.registerAutomatically = true;

    After that, all InteractiveObjects on the stage should dispatch mouse events, so you can normally attach event listeners to them and do whatever you want in them:

    myBox.addEventListener(MouseEvent.MOUSE_WHEEL, function(event:MouseEvent):void {
        t.text = ("Mouse wheel delta: "+event.delta);

The code could probably use some debugging and optimization, but it seems to work well if you're not doing anything too fancy. If you take it and make any fixes, please let me know! ;)

A working example.
The source code for the example.
The AsDoc-generated API Documentation for the support library

This code is distributed under the MIT License.


techheadlines.org » Blog Archive » OS X Mouse wheel support for Flex 2 applications July 6, 2007 at 2:00 PM

[…] OS X Mouse wheel support for Flex 2 applicationsIn my current job I have been programming user interfaces for applications that display networks of data (as in nodes, links etc.) with the Adobe Flex framework, and the UI paradigm I have been utilizing is a kind of a Zoomable User Interface (ZUI) …. […]

Nicolas July 13, 2007 at 6:27 AM

Hey mate. Great solution, works well in Safari. However, I couldn’t get it to work in Camino. As far as I know, Camino uses the same engine than Firefox?… Could you have a look and let me/us know?

thanks in advance.

Hasse G July 13, 2007 at 9:02 AM

Hey Nicolas.

I modified the javascript to work with other OS X browsers, too. See the post for more details. :)

Alex K. July 20, 2007 at 2:27 AM

Nice work. I was going to use SWFMacMouseWheel, only to find that it was AS2. I just searched through it and found your post. Again, nice work.

geza August 18, 2007 at 3:11 AM

Nice stuff, I have the same trap: dev on macBook fo’ win users.. :) but guys.. I just can’t make it work It’s like:

The error console sais:

1120: Access of undefined property _mwSupport.

Why It doesen’t recognise it?


geza August 18, 2007 at 3:18 AM

akay.. you can check it out here.. http://www.figurart.hu/test.mxml

Hasse G August 19, 2007 at 7:14 PM

Hi Geza,

Well, you seem to be declaring the variable _mwSupport properly, so that shouldn’t be a problem. In the code you posted, I don’t really see anything wrong. I would just make sure that you actually have an object with the id redArea in there.

Philip Flip Kromer August 25, 2007 at 8:13 AM

Hi, This is great stuff – thanks for figuring this out.

Would you please clarify the license attached to this code? In the US and many other countries, if no copyright is specified then all rights are reserved – so I can’t include your excellent work in other projects.

If you’d like to let anyone do whatever they want with the code, the MIT license is probably easiest: http://www.opensource.org/licenses/mit-license.php

Cheers, flip

Bernhard August 31, 2007 at 7:40 PM

In my dev environment using “file://” your code works fine, but it doesn’t as soon as I use “http://”. It doesn’t even brings up an error message.

I have no clue why. Do you have any hints for me??

Regards, Bernhard

Hasse G August 31, 2007 at 7:46 PM

Bernhard: Your problem probably has to do with Flash Player’s security sandbox features and the ExternalInterface. Make sure that the javascript file is in the same host and port as the .swf and the page that embeds the .swf and you should be fine.

nala September 22, 2007 at 11:51 PM

Nice Site!

David desieb September 30, 2007 at 3:21 PM

Hi there! Nice work, Just a dumb question though (I’m not use to Flex, not sure to know what it is): does this mean that we can add the mouse wheel support (for scrollPanes or whatever) on flash websites (no Flex) ? Tks for your answer

Hasse G October 1, 2007 at 10:51 AM

Hi David.

This code is ActionScript 3 and it relies on the use of some Flex classes, but it can be adapted for non-Flex AS3 – I just haven’t done it. If you do, please send me the code or the link to the code and I’ll post it here for others as well. If you use AS2, check out the following link:


danielyuen October 3, 2007 at 10:24 AM

thank you

maxim October 7, 2007 at 12:01 AM

Hasseg, you are a genius.

mike October 7, 2007 at 5:06 PM

Unfortunely the example is not working with Opera version 9.23

Bram November 7, 2007 at 3:57 PM

Thanks for this project Hasseg, however; your example does not work on Win XP SP2 - IE … Any thoughts?


Hasse G November 7, 2007 at 4:32 PM


I Tried to fix it for the new Opera version but couldn’t find a quick fix and I haven’t had time to go into it more deeply. It has something to do with JavaScript not being able to listen for mouse events inside the div that contains the Flash app, or more likely that Opera just uses some other method for doing it that I couldn’t figure out when I tried to fix it.


It seems to work fine on WinXP SP2 when using Firefox. I Don’t have the proper access rights to update the ActiveX Flash player on my work computer (the only Windows box I have available), and it currently has Flash player 8 on it so I can’t test it :( Sorry..

Bram November 7, 2007 at 4:45 PM


FF & Opera 9.24 work just fine on Windows for me, Internet Explorer is an issue, as I can not see the example. The page is completely empty, as in total blank :).

Takeshi November 11, 2007 at 9:04 PM

In case of Vista + IE7?

Bram November 12, 2007 at 11:40 AM

Win XP SP2

Anthony Picciano November 27, 2007 at 9:47 PM

I tried implementing your mouse scroll wheel support using Flex 3 and it worked great locally, but when I put the site up on our web server, it did not work. I had the “allowScriptAccess” set to “sameDomain”, but no go. Do you know if your code should work correctly with Flex 3? Thanks!

Hasse G November 28, 2007 at 5:48 PM

Hey Anthony,

I haven’t tried Flex 3 at all so I can’t say if this’ll work with it. For what it’s worth, I believe it should work and your problem is probably based somewhere else, but I can’t say for sure. I Apologize for not having more useful advice but I unfortunately haven’t had time to work on this stuff lately. :(

Laurent November 30, 2007 at 10:59 PM

Very good job!


Melvyn December 3, 2007 at 6:55 PM

Bram, I could avoid the bug in IE by wrapping the JS code in the html page in a conditional tag :

var mw_flashMovieId = "flashMovie"; // the id/name of your flash app's HTML DOM element     
var mw_flashContainerId = "flashContainerDiv"; // the id/name of the flash element's surrounding div element  
Melvyn December 3, 2007 at 6:59 PM

guuhhh all tags were stripped in my previous message :(

here’s the code : http://toolateatnight.be/macmousewheel/

Bram December 3, 2007 at 6:59 PM

Thanks Melvyn, It works on my projects, but not on the example pages provided on this site :)

Melvyn December 3, 2007 at 7:00 PM

all right ;)

Jamie December 6, 2007 at 6:39 AM

I used your solution for getting MouseWheel support on Macs and it is fabulous! A while later I discovered that setting wmode=opaque breaks Flash’s MouseWheel in Firefox 2 on Windows. A google search shows it has been a major problem for a lot of Flex developers. So what I did was fall back to your solution. I just commented out the following conditional statement in osxmousewheel.js

//if (navigator.userAgent.indexOf(‘Mac’) != -1)

Now I can have wmode=opaque AND MouseWheel in IE, Firefox, and Safari on both Windows and Mac.

Jonathan Campos January 7, 2008 at 10:45 PM

If anyone has any information on making this work in Flex 3 that would be most helpful. I really can’t figure out why it isn’t working, but it works on my local box and not on my server. Also I moved my files to get the error to popup in the local environment and I got this:

TypeError: Error #1009: Cannot access a property or method of a null object reference. at mx.managers::PopUpManagerImpl/addPopUp()[E:\dev\flex_3_beta3\sdk\frameworks\projects\framework\src\mx\managers\PopUpManagerImpl.as:229] at mx.managers::PopUpManager$/addPopUp()[E:\dev\flex_3_beta3\sdk\frameworks\projects\framework\src\mx\managers\PopUpManager.as:167] at mx.controls::Alert$/show()[E:\dev\flex_3_beta3\sdk\frameworks\projects\framework\src\mx\controls\Alert.as:505] at org.hasseg.externalMouseWheel::ExternalMouseWheelSupport/initialize()[/Users/jonathan/Documents/Flex Builder 3/dflex/src/org/hasseg/externalMouseWheel/ExternalMouseWheelSupport.as:64] at org.hasseg.externalMouseWheel::ExternalMouseWheelSupport()[/Users/jonathan/Documents/Flex Builder 3/dflex/src/org/hasseg/externalMouseWheel/ExternalMouseWheelSupport.as:43] at org.hasseg.externalMouseWheel::ExternalMouseWheelSupport$/get instance()[/Users/jonathan/Documents/Flex Builder 3/dflex/src/org/hasseg/externalMouseWheel/ExternalMouseWheelSupport.as:51] at dflex()[/Users/jonathan/Documents/Flex Builder 3/dflex/src/com/dflex/controllers/application.as:18] at _dflex_mx_managers_SystemManager/create() at mx.managers::SystemManager/initializeTopLevelWindow()[E:\dev\flex_3_beta3\sdk\frameworks\projects\framework\src\mx\managers\SystemManager.as:2436] at mx.managers::SystemManager/docFrameHandler()[E:\dev\flex_3_beta3\sdk\frameworks\projects\framework\src\mx\managers\SystemManager.as:2328]


Sebastian Zarzycki January 16, 2008 at 12:55 PM

Exact same behaviour on my machines. Can you produce a solution for Flex 3?

Ali Rantakari January 16, 2008 at 2:10 PM

Hi guys, I don’t have Flex 3 installed nor have I time to start debugging this with it, but from the error message it seems that it’s failing in the initialize() method:

private function initialize():void {
	try {
		ExternalInterface.addCallback("dispatchExternalMouseWheelEvent", externalMouseWheelEventHandler);
		Alert.show("Error initializing ExternalMouseWheelSupport: "+e.toString());

It’s clear that the ExternalInterface method calls are causing a problem there, so I think the way to start debugging is to check if any security features are blocking it.

Clayton January 23, 2008 at 6:28 AM

stab in the dark… allowScriptAccess=“samedomain” ?

Ryan January 31, 2008 at 12:47 AM

Anyone close to converting this for AS3 use in Flash, rather than Flex?

Melvyn January 31, 2008 at 1:21 PM


Sources : http://toolateatnight.be/macmousewheel/mac_mousewheel_AS3.zip

I modified the class in a new one “ExternalMouseWheelSupportFlash.as” with the Flex-specific stuff stripped out.

Johan Sundhage February 8, 2008 at 1:32 PM

Yay!! This made my day. Thanks thanks thanks.

I made it work with Flash AS3.

Melvyn February 8, 2008 at 1:45 PM

PixelBreaker has updated his mac mousewheel support for AS3 : http://blog.pixelbreaker.com/flash/as30-mousewheel-on-mac-os-x/

Ali Rantakari February 8, 2008 at 1:52 PM

Thanks for the info, Melvyn. I Put a link to the top of the page for that to guide people looking for an AS3-only solution there.

Jamie McDaniel March 1, 2008 at 4:16 AM

Just a note. The PixelBreaker solution will work with all Flex applications, not just AS3 projects. Just change the line in the PixelBreaker example:




I put this line in my applicationComplete event handler, although it may work elsewhere.

The GAE SWF Project version 1.34 at Aral Balkan April 25, 2008 at 2:17 AM

[…] the mouse wheel work in Flash on OS X (it doesn’t by default) by using Ali Rantakari’s excellent ExternalMouseWheelSupport package. The The GAE SWF Project version 1.34 article by Aral Balkan, unless otherwise expressly […]

Ali Rantakari April 26, 2008 at 10:41 PM

Hey everyone, just posting this into the comments here in case someone has subscribed and would thus like to be informed of this.

I’ve just made a post about the new version (2) of this solution – check it out:


Pathfinder Development » Mouse wheel (scroll) Event in Flash Player running on a Mac September 18, 2008 at 8:59 PM

[…] You can find the full explenation on this blog post. […]

Kelso’s Corner » Blog Archive » Mac OS X Mouse Wheel Support for ActionScript 3 Flash Applications (v.2+) (Hasseg) January 9, 2009 at 7:47 AM

[…] I’ve finally updated the solution I’ve made earlier for enabling Mac OS X mouse wheel support in Flex applications to a second version. I didn’t want to continue adding stuff into the original post, so I decided […]

Thomas Q. Brady September 2, 2009 at 7:51 PM

Awesome. Thanks!!