Sending and Receiving Data From Servers

Making a request from Flash

The URLRequest and URLLoader classes work together to make requests from Flash to external resources. The URLRequest defines information about the request e.g. the request body and the request method type, and the URLLoader references this to perform the actual request and provide a means of being notified when a response is received from the resource.

Example:

var request:URLRequest = new URLRequest('https://stackoverflow.com');
var loader:URLLoader = new URLLoader();

loader.addEventListener(Event.COMPLETE, responseReceived);
loader.load(request);

function responseReceived(event:Event):void {
    trace(event.target.data); // or loader.data if you have reference to it in
                              // this scope.
}

Adding variables to your request

The URLVariables class allows you to define data to be sent along with a URLRequest.

Example:

var variables:URLVariables = new URLVariables();

variables.prop = "hello";
variables.anotherProp = 10;

var request:URLRequest = new URLRequest('https://someservice.com');
request.data = variables;

You can either send the request via a URLLoader or open the request URL with the variables attached in the querystring using navigateToURL.

Altering the HTTP method (GET, POST, PUT, etc)

The URLRequestMethod class contains constants for the various request types you can make. These constants are to be allocated to URLRequest’s method property:

var request:URLRequest = new URLRequest('https://someservice.com');
request.method = URLRequestMethod.POST;

Note that only GET and POST are available outside the AIR runtime.

My response data is always null, what does “asynchronous” mean?

When Flash makes a request for data from an external source, that operation is asynchronous. The most basic explanation of what this means is that the data loads “in the background” and triggers the event handler you allocate to Event.COMPLETE when it is received. This can happen at any point in the lifetime of your application.

Your data WILL NOT be available immediately after calling load() on your URLLoader. You must attach an event listener for Event.COMPLETE and interact with the response there.

var request:URLRequest = new URLRequest('https://someservice.com');
var loader:URLLoader = new URLLoader();

loader.addEventListener(Event.COMPLETE, responseReceived);
loader.load(request);

trace(loader.data); // Will be null.

function responseReceived(event:Event):void {
    trace(loader.data); // Will be populated with the server response.
}

trace(loader.data); // Will still be null.

You cannot get around this with any little tricks like using setTimeout or similar:

setTimeout(function() {
    trace(loader.data); // Will be null if the data hasn't finished loading
                        // after 1000ms (which you can't guarantee).
}, 1000);

Cross-domain requests

Flash will not load data from a domain other than the one your application is running on unless that domain has an XML crossdomain policy either in the root of the domain (e.g. https://somedomain.com/crossdomain.xml) or somewhere that you can target with Security.loadPolicyFile(). The crossdomain.xml file is where you can specify domains that are able to ask your server for data from a Flash application.

Example of the most permissive crossdomain.xml:

<?xml version="1.0" ?>
<cross-domain-policy>
  <allow-access-from domain="*"/>
  <allow-http-request-headers-from domain="*" headers="*"/>
</cross-domain-policy>

Note this example should not be used in production environments, use a more restrictive instance.

A more restrictive specific crossdomain.xml will look like this for example:

<?xml version="1.0"?>
<!DOCTYPE cross-domain-policy SYSTEM "https://www.macromedia.com/xml/dtds/cross-domain-policy.dtd">
<cross-domain-policy>
    <site-control permitted-cross-domain-policies="master-only" />

    <allow-access-from domain="*.domain.com" to-ports="80,843,8011" /> 
    <allow-access-from domain="123.123.123.123" to-ports="80,843,8011" /> 
</cross-domain-policy>

Resources:

The crossdomain policy file specification.