Blue Flex

Today while coding I was creating some classes that required them to dispatch custom events. I know that this is a fairly common thing to do but sometimes it is these little things that can trip you up or take a while to find out how to do them.

So I thought that each time I come across something that is ‘simple’ (only simple after you know it!) that I’ll try to create a quick blog entry and take note of it.  Each time I create a new ‘tip’ post I’ll link it to the previous/next tip so that it will be quick and easy to browse through a load of tips.
 

Tip #1

So for my first tip, this is how to implement your own custom events.

First if you are firing the events from a custom MXML file then you need to create a metadata tag. I make this the first node inside the MXML file.  For example:

<?xml version="1.0" encoding="utf-8"?>
<mx:Canvas xmlns:mx="http://www.adobe.com/2006/mxml"
		width="500"
		height="300"
		>
 
<mx:Metadata>
<!-- 
First two event are plain string events, they do not pass any specific data with them -->
<!-- 
The last event is a custom class that extends Event and as such you need to give
it its package name + the class name as the type -->
	[Event('next')]
	[Event('previous')]
	[Event(name='jump', type='com.kennethsutherland.events.JumpEvent')]
</mx:Metadata>
...

If your custom class is an AS3 file then you would put something like the following are the imports

[Event(name="previous", type="flash.events.Event")]
[Event(name='jump', type='com.kennethsutherland.events.JumpEvent')]

Then inside the MXML file (script block) or anywhere in the AS3 file to fire the event I’d do the following:
 

//custom event, the extra value is handled by the JumpEvent class
dispatchEvent(new JumpEvent("jump", specificValueForTheJumpEventClass));
//standard event
dispatchEvent(new Event("next"));

If you do the above and lets just say your MXML/AS file is called ‘GreatComponent’ then in order to use the new custom event, its as simple as the below bit of code. 

<local:GreatComponent
    next="doSomething()"
    jump="doSomethingElse(event)"
/>

That’s it, now you can fire of any custom event that you wish and make sure that it gets listened to.