/* AS3
	Copyright 2009 urbanINFLUENCE.
*/
package org.natemiller.types {
	import fl.motion.easing.*;
	import flash.display.*;
	import flash.events.*;
	import flash.net.*;
	import flash.utils.Timer;
	
	import org.natemiller.events.AssetEvent;
	/*
	*	Generic base class for a loadable asset
	*
	*	@langversion ActionScript 3.0
	*	@playerversion Flash 9.0
	*
	*	@author 
	*	@since  13.02.2009
	*/
	public class Asset implements IEventDispatcher {
		
		//--------------------------------------
		// CLASS CONSTANTS
		//--------------------------------------
		
		//--------------------------------------
		//  CONSTRUCTOR
		//--------------------------------------
		
		public function Asset() {
		}
		
		//--------------------------------------
		//  VARIABLES
		//--------------------------------------
		
		public static var base_path:String = "";
		protected static var _assets:Array = [];
		protected static var _hshAssets:Object = {};
		
		protected var dispatcher:EventDispatcher;
		
		public var data:Object = {};	// public object for dynamic property setting
		private var _assetLoader:Loader;
		private var _path:String;
		private var _hasLoadError:Boolean = false;		// whether an error was triggered while loading
		private var _isLoaded:Boolean = false;				// if the image successfully loaded
		private var _percentLoaded:int = 0;				// the percentage loaded
		private var _timerMonitorProcess:Timer;		// a timer used to monitor load progress
		
		//--------------------------------------
		//  GETTER/SETTERS
		//--------------------------------------
		
		
		public function get content() : Loader { 
			return _assetLoader; 
		}
		
		public function get isLoaded() : Boolean { 
			return _isLoaded; 
		}
		
		public function get percentLoaded() : int { 
			return _percentLoaded; 
		}
		
		//--------------------------------------
		//  PUBLIC METHODS
		//--------------------------------------
		
		/**
		* Initializes the asset instance
		*/
		public function initialize(path:String) : void {
			_path = path;
			_assetLoader = new Loader();
			dispatcher = new EventDispatcher(this);
		} // end initialize
		
		
		public function addEventListener(type:String, listener:Function, useCapture:Boolean = false, priority:int = 0, useWeakReference:Boolean = false):void{
       dispatcher.addEventListener(type, listener, useCapture, priority);
    }
           
    public function dispatchEvent(evt:Event):Boolean{
       return dispatcher.dispatchEvent(evt);
    }
    
    public function hasEventListener(type:String):Boolean{
       return dispatcher.hasEventListener(type);
    }
    
    public function removeEventListener(type:String, listener:Function, useCapture:Boolean = false):void{
       dispatcher.removeEventListener(type, listener, useCapture);
    }
                   
    public function willTrigger(type:String):Boolean {
       return dispatcher.willTrigger(type);
    }

		/**
		* public string method
		*/
		public function toString() : String {
			return "[Asset path: " + _path + "]";
		} // end toString
		
		/**
		* Loads the asset into mem
		*/
		public function load() : void {
			if (_isLoaded || _hasLoadError) {
				trace("[Asset.load]: Warning - you've already attempted to load this asset. Halting load execution.");
				return;
			}
			
			
			_assetLoader.contentLoaderInfo.addEventListener(Event.INIT, onAssetLoaded, false, 0, true);
			_assetLoader.contentLoaderInfo.addEventListener(IOErrorEvent.IO_ERROR, onAssetLoadError, false, 0, true);
			beginAssetLoadProgressMonitor();
			_assetLoader.load( new URLRequest(_path));
		} // end load
		

		//--------------------------------------
		//  EVENT HANDLERS
		//--------------------------------------
		
		/**
		* Called when the photo has completed loading
		*/
		protected function onAssetLoaded(e:Event) : void {
			killAssetLoadProgressMonitor();
			_percentLoaded = 100;
			_isLoaded = true;
			dispatchEvent(new AssetEvent(AssetEvent.LOADED, true, false, this));
			disposeListeners();
		} // end onAssetLoaded
		
		/**
		* Called when the photo has failed to load
		*/
		protected function onAssetLoadError(e:IOErrorEvent) : void {
			trace(e);
			_hasLoadError = true;
			disposeListeners();
		} // end onAssetLoadError
		
		/**
		* Called each time the load progress monitor ticks, updates the load percentage
		*/
		protected function onMonitorLoadTick(e:TimerEvent = null) : void {
			var bLoaded:Number = _assetLoader.contentLoaderInfo.bytesLoaded;
			var bTotal:Number = _assetLoader.contentLoaderInfo.bytesTotal;
			if (bLoaded > 0 && bTotal > 0) {
				_percentLoaded = Math.round(bLoaded / bTotal * 100);
			} else _percentLoaded = 0;
		} // end onMonitorLoadTick
		
		//--------------------------------------
		//  PRIVATE & PROTECTED INSTANCE METHODS
		//--------------------------------------
		
		/**
		* Trashes any listeners no longer needed. Triggered by either an error or load complete event
		*/
		protected function disposeListeners() : void {
			_assetLoader.removeEventListener(Event.INIT, onAssetLoaded);
			_assetLoader.removeEventListener(IOErrorEvent.IO_ERROR, onAssetLoadError);
		} // end disposeListeners
		
		
		/**
		* Starts a monitor process to update the load amount for the photo
		*/
		protected function beginAssetLoadProgressMonitor() : void {
			_timerMonitorProcess = new Timer(100);	// execute check every 100 ms
			_timerMonitorProcess.addEventListener(TimerEvent.TIMER, onMonitorLoadTick, false, 0, true);
			onMonitorLoadTick(); // fires to make sure that this is called at least once
			_timerMonitorProcess.start();
		} // end beginPhotoLoadProgressMonitor
		
		/**
		* Destroys the photo progress monitor
		*/
		protected function killAssetLoadProgressMonitor() : void {
			_timerMonitorProcess.stop();
			_timerMonitorProcess.removeEventListener(TimerEvent.TIMER, onMonitorLoadTick);
		} // end killPhotoLoadProgressMonitor
		
	} // end Asset
	
} // end package


/* AS3
	Copyright 2009 urbanINFLUENCE.
*/
package org.natemiller.events {
	import flash.events.Event;
	import org.natemiller.types.Asset;
	
	/*
	*	Event sublcass used for assets
	*
	*	@langversion ActionScript 3.0
	*	@playerversion Flash 9.0
	*
	*	@author 
	*	@since  13.02.2009
	*/
	public class AssetEvent extends Event {
		
		//--------------------------------------
		// CLASS CONSTANTS
		//--------------------------------------
		
		public static const LOADED : String = "assetLoaded";
		
		//--------------------------------------
		//  CONSTRUCTOR
		//--------------------------------------
		
		public function AssetEvent( type:String, bubbles:Boolean=true, cancelable:Boolean=false, asset:Asset = null ){
			super(type, bubbles, cancelable);		
			_asset = asset;
		}
		
		
		public function get asset() : Asset { 
			return _asset; 
		}
		

		override public function clone() : Event {
			return new AssetEvent(type, bubbles, cancelable, _asset);
		}
		
		private var _asset:Asset;
		
	}
	
}

A simple class and event which can be used to load external assets

Flash: External asset class

flash

ActionScript 3