Using ModuleLoader events in flex

http://livedocs.adobe.com/flex/3/html/help.html?content=modular_6.html

<?xml version="1.0"?>
<!-- modules/EventApp.mxml -->
<mx:Application xmlns="*" xmlns:mx="http://www.adobe.com/2006/mxml">
    <mx:Script>
        <![CDATA[
            [Bindable]
            public var selectedItem:Object;
        ]]>
    </mx:Script>
    <mx:ComboBox 
        width="215" 
        labelField="label" 
        close="selectedItem=ComboBox(event.target).selectedItem"
    >
        <mx:dataProvider>
            <mx:Object label="Select Coverage"/>        
            <mx:Object 
                label="Life Insurance" 
                module="insurancemodules/LifeInsurance.swf"
            />
            <mx:Object 
                label="Auto Insurance" 
                module="insurancemodules/AutoInsurance.swf"
            />          
            <mx:Object 
                label="Home Insurance" 
                module="insurancemodules/HomeInsurance.swf"
            />
        </mx:dataProvider>
    </mx:ComboBox>

    <mx:Panel width="100%" height="100%">
        <CustomModuleLoader id="mod" 
            width="100%" 
            url="{selectedItem.module}"
        />
    </mx:Panel>
    <mx:HBox>
        <mx:Button label="Unload" click="mod.unloadModule()"/> 
        <mx:Button label="Nullify" click="mod.url = null"/>
    </mx:HBox>  
</mx:Application> 

<?xml version="1.0" encoding="iso-8859-1"?>
<!-- modules/CustomModuleLoader.mxml -->
<mx:ModuleLoader xmlns:mx="http://www.adobe.com/2006/mxml" xmlns="*" creationComplete="init()">
  <mx:Script>
    <![CDATA[
    public function init():void {
        addEventListener("urlChanged", onUrlChanged);
        addEventListener("loading", onLoading);
        addEventListener("progress", onProgress);
        addEventListener("setup", onSetup);
        addEventListener("ready", onReady);
        addEventListener("error", onError);
        addEventListener("unload", onUnload);

        standin = panel;
        removeChild(standin);        
    }
    
    public function onUrlChanged(event:Event):void {
        if (url == null) {
            if (contains(standin))
                removeChild(standin);
        } else {
            if (!contains(standin))
                addChild(standin);
        }
        progress.indeterminate=true;
        unload.enabled=false;
        reload.enabled=false;
    }

    public function onLoading(event:Event):void {
        progress.label="Loading module " + url;
        if (!contains(standin))
            addChild(standin);

        progress.indeterminate=true;
        unload.enabled=false;
        reload.enabled=false;
    }
    
    public function onProgress(event:Event):void {
        progress.label="Loaded %1 of %2 bytes...";
        progress.indeterminate=false;
        unload.enabled=true;
        reload.enabled=false;
    }
    
    public function onSetup(event:Event):void {
        progress.label="Module " + url + " initialized!";
        progress.indeterminate=false;
        unload.enabled=true;
        reload.enabled=true;
    }
    
    public function onReady(event:Event):void {
        progress.label="Module " + url + " successfully loaded!";
        unload.enabled=true;
        reload.enabled=true;

        if (contains(standin))
            removeChild(standin);
    }
    
    public function onError(event:Event):void {
        progress.label="Error loading module " + url;
        unload.enabled=false;
        reload.enabled=true;
    }
    
    public function onUnload(event:Event):void {
        if (url == null) {
            if (contains(standin))
                removeChild(standin);
        } else {
            if (!contains(standin))
                addChild(standin);
        }
        progress.indeterminate=true;
        progress.label="Module " + url + " was unloaded!";
        unload.enabled=false;
        reload.enabled=true;
    }
    
    public var standin:DisplayObject;
    ]]>
  </mx:Script>

  <mx:Panel id="panel" width="100%">
    <mx:ProgressBar width="100%" id="progress" source="{this}"/>
    <mx:HBox width="100%">
      <mx:Button id="unload" 
        label="Unload Module" 
        click="unloadModule()"
      />
      <mx:Button id="reload" 
        label="Reload Module" 
        click="unloadModule();loadModule()"
      />
    </mx:HBox>
  </mx:Panel>
</mx:ModuleLoader>