Actionscript – confused about HttpService’s useProxy (Flex 3)

actionscriptactionscript-3apache-flexflex3mxml

I have a flex app, where the user can provide a link to a resource. I want to perform a simple validation and check if the url is actually valid (not just structure, but actually test the link to ensure I get a 200 OK).

I figured I would just use HttpService and use the HEAD method, but it seems that this is only available when you set useProxy to true, but I tried that and I still get errors; so I am pretty sure I am doing something wrong….here is a snippet of the code

var service:HTTPService = new HTTPService();
service.method = "HEAD"; 
service.url = url;
service.useProxy = true;
service.addEventListener(ResultEvent.RESULT, result);       
service.addEventListener(FaultEvent.FAULT, error);       
service.send();

Any idea what I am doing wrong? I am also open to other suggestions as to how to check if a url is valid (I would prefer to do this directly from Flex, without having to go back & forth to the server). Thanks.

EDIT (8/13/2009)

I implemented a simple UrlValidator by using a UrlLoader and assigning 2 listeners on it. one for IOError, and the other for Progress. My thinking was that Progress would act similar to a HEAD call, and I could just kill the stream after some amount of data was received. Unfortunately, the progress event is called in the case of a 404 or 403, which defeats the purpose. I also tried this with the Open event, but got the same results. Any ideas?

Best Answer

Adobe's Flex docs state: "When you do not go through the server-based proxy service, you can use only HTTP GET or POST methods. However, when you set the useProxy property to true and you use the server-based proxy service, you can also use the HTTP HEAD, OPTIONS, TRACE, and DELETE methods."

The server-based proxy service is referring to Live Cycle Data Services

I know AIR supports HEAD requests using the ServiceMonitor, but it looks like Flex on it's own doesn't.

Having a quick search around, it looks a few people have used sockets to roll their own custom URLLoader classes which can access the request headers - you could try one of them

Related Solutions

Possible to use Flex Framework/Components without using MXML

I did a simple bootstrap similar to Borek (see below). I would love to get rid of the mxml file, but if I don't have it, I don't get any of the standard themes that come with Flex (haloclassic.swc, etc). Does anybody know how to do what Theo suggests and still have the standard themes applied?

Here's my simplified bootstrapping method:

main.mxml

<?xml version="1.0" encoding="utf-8"?>
<custom:ApplicationClass xmlns:custom="components.*"/>

ApplicationClass.as

package components {
    import mx.core.Application;
    import mx.events.FlexEvent;
    import flash.events.MouseEvent;
    import mx.controls.Alert;
    import mx.controls.Button;

    public class ApplicationClass extends Application {
        public function ApplicationClass () {
            addEventListener (FlexEvent.CREATION_COMPLETE, handleComplete);
        }
        private function handleComplete( event : FlexEvent ) : void {
            var button : Button = new Button();
            button.label = "My favorite button";
            button.styleName="halo"
            button.addEventListener(MouseEvent.CLICK, handleClick);
            addChild( button );
        }
        private function handleClick(e:MouseEvent):void {
            Alert.show("You clicked on the button!", "Clickity");
        }
    }
}

Here are the necessary updates to use it with Flex 4:

main.mxml

<?xml version="1.0" encoding="utf-8"?>
<local:MyApplication xmlns:fx="http://ns.adobe.com/mxml/2009" xmlns:local="components.*" />

MyApplication.as

package components {
    import flash.events.MouseEvent;
    import mx.controls.Alert;
    import mx.events.FlexEvent;
    import spark.components.Application;
    import spark.components.Button;

    public class MyApplication extends Application {
        public function MyApplication() {
              addEventListener(FlexEvent.CREATION_COMPLETE, creationHandler);
        }
        private function creationHandler(e:FlexEvent):void {
            var button : Button = new Button();
            button.label = "My favorite button";
            button.styleName="halo"
            button.addEventListener(MouseEvent.CLICK, handleClick);
            addElement( button );
        }
        private function handleClick(e:MouseEvent):void {
            Alert.show("You clicked it!", "Clickity!");
        }
    }
}

Xml – Flex – URLLoader and HTTPService

HTTPService inherits AbstractInvoker which allows you to use tokens and responders which you cannot use with URLLoader. Tokens are good when you need to pass specific variables that are relevant to the request, which you want returned with the response.

Other than that, using URLLoader or HttpService to load xml is the same.

Example:

var token:AsyncToken = httpService.send({someVariable: 123});
token.requestStartTime = getTimer();
token.addResponder(new AsyncResponder(
    function (evt:ResultEvent, token:Object):void {
        var xml:XML = evt.result as XML;
        var startTime = token.requestStartTime;
        var runTime = getTimer() - startTime;
        Alert.show("Request took " + runTime + " ms");
        //handle response here
    },
    function (info:Object, token:Object):void {
        //handle fault here
    },
    token
));

Best Answer

Related Solutions

Possible to use Flex Framework/Components without using MXML

Xml – Flex – URLLoader and HTTPService

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