If you are making a HTTPService call in Flex, you need to make sure that the domain specified in the url attribute is the domain from where your application was downloaded or there is a crossdomain.xml file granting access to your application’s originating is available on the domain specified in the HTTPService url attribute.
Take a look at the following example. Trying to load a XML file :-
<s:HTTPService resultFormat="e4x" result="resultHandler(event)" id="serv" url="http://news.bbc.co.uk/nol/shared/bsp/hi/services/desktop_alerts/xml/ukfs/alert_data.xml" />
If you run the above code, you get the following error :-
[RPC Fault faultString="Security error accessing url" faultCode="Channel.Security.Error" faultDetail="Destination: DefaultHTTP"] at mx.rpc::AbstractInvoker/http://www.adobe.com/2006/flex/mx/internal::faultHandler()[E:\dev\4.x\frameworks\projects\rpc\src\mx\rpc\AbstractInvoker.as:345] at mx.rpc::Responder/fault()[E:\dev\4.x\frameworks\projects\rpc\src\mx\rpc\Responder.as:68] at mx.rpc::AsyncRequest/fault()[E:\dev\4.x\frameworks\projects\rpc\src\mx\rpc\AsyncRequest.as:113] at DirectHTTPMessageResponder/securityErrorHandler()[E:\dev\4.x\frameworks\projects\rpc\src\mx\messaging\channels\DirectHTTPChannel.as:432] at flash.events::EventDispatcher/dispatchEventFunction() at flash.events::EventDispatcher/dispatchEvent() at flash.net::URLLoader/redirectEvent()
This means the URL we are trying to access does not have a crossdomain.xml file. And as is obvious, we can not ask for one in every case.
As I started looking into YQL recently, I figured this could be done with YQL. Here is a complete example I came up with that uses YQL to query the same URL that we could not access above and it parses the XML and displays in a grid.
<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/mx" minWidth="955"
minHeight="600" initialize="doInit()">
<fx:Declarations>
<!-- Place non-visual elements (e.g., services, value objects) here -->
<s:HTTPService resultFormat="e4x"
result="resultHandler(event)"
id="serv"
url="{yql_url('http://news.bbc.co.uk/nol/shared/bsp/hi/services/desktop_alerts/xml/ukfs/alert_data.xml')}" />
</fx:Declarations>
<fx:Script>
<![CDATA[
import mx.rpc.events.ResultEvent;
[Bindable] private var items:XMLList ;
private function doInit():void
{
serv.send();
}
private function yql_url(url:String):String
{
var str:String = 'http://query.yahooapis.com/v1/public/yql?q=';
var query:String = 'select * from xml where url="';
query = query + url + '"';
return str + encodeURI(query);
}
private function resultHandler(event:ResultEvent):void
{
var data:XML = new XML(String(event.result));
items = data.results.stories.story;
}
]]>
</fx:Script>
<mx:DataGrid id="newsList" dataProvider="{items}" width="500" height="200">
<mx:columns>
<mx:DataGridColumn dataField="headline" />
</mx:columns>
</mx:DataGrid>
</s:Application>
Basically, what is happening here is I am sending a query to the YQL which looks something like this.
http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20xml%20where%20url%3D'http%3A%2F%2Fnews.bbc.co.uk%2Fnol%2Fshared%2Fbsp%2Fhi%2Fservices%2Fdesktop_alerts%2Fxml%2Fukfs%2Falert_data.xml'
That does the trick. Returns me an XML as I wanted and then its upto me to do whatever I want with the XML.
I am actually wondering why is YQL not as widely used or heard about as it should be.
