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Flex Design Patterns

Flex Singleton Class

Written by Philip

The Singleton class, which can be used in Flex / Flash, which are of course coded in AS3, is designed to restrict instantiation of a class to only one object. It's great when you only want one object across the whole of your application. An example could be you load in a load of xml data and you want to store the values of the xml for use throughout the application. In Flex / Flash we can write a Singleton Class like the following. We use the getInstance() to return the object created.

 

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package com.howtocode
{
	[Bindable]
	public class Singleton
	{
 
        	/** Only one instance of the model locator **/
 
        	private static var instance:Singleton = new Singleton();
 
        	/** Bindable Data **/
 
        	public var flexData:String = "SuperApp";
		public var userScore:int = 0;
 
       	 	public function Singleton()
		{
			if(instance)
			{
				throw new Error ("We cannot create a new instance.
 Please use Singleton.getInstance()");
			}
		}
 
		public static function getInstance():Singleton
		{
			return instance;
		}
	}
}


Singleton Class Access

To access a variable from the Singleton class we use the following.

 

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import com.howtocode.Singleton;
 
private var model:Singleton = Singleton.getInstance();
 
// To retrieve flexData String from Singleton Class use model.flexData
trace(model.flexData);
 
// To set flexData String in Singleton Class use the following
model.flexData = "FlexApp"

 

You can of course do something really cool which is place something like place

 

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<mx:Button id="flexButton" label="{model.flexData}">

 

into you're MXML and when flexData is changed in your Singleton Class it automatically updates you're MXML as we've set the whole Singleton Class as [bindable].