How to send array through HTTPservice in Adobe Flex 3

I am not quite sure what you mean by sending an array to a httpservice. If you mean to send an array to a httpservice with the same field name, you can pass an array as field value.

var service:HTTPService = new HTTPService();
service.useProxy = true;
service.destination = "myservicet";
service.resultFormat = HTTPService.RESULT_FORMAT_XML;

var fields:Array = ["categories", "organisation"];
var params:Object = new Object();
params.q = "stackoverflow";
params.rows = 0;
params.facet = "true";
params["facet.field"] = fields;
service.send(params);

The HTTPService will convert this to the url parameters:

facet=true&q=stackoverflow&facet%2Efield=categories&facet%2Efield=organisation&rows=0

Hope this helps!

Added for more clarity. When there is only 1 argument in the array, do not pass the fields as an array. For some reason, flex will not send this to the http service

It really depends what is the back end technology you're using. If you're sending it to PHP you could try:

var fields:Array = ["categories", "organisation"];
var params:Object = {};
params.q = "stackoverflow";
params.rows = 0;
params.facet = "true";
params["facet.field[]"] = fields;
service.send(params);

PHP will generate an array for you. AFAIR this works fine in Rails as well.

if it is a simple string array, you can join it with a well know separator char, and on the other site, split the string with the same separator back to an array.

If it is a simple array, you could send it as a comma separated string.

httpService.request = new Object;
httpService.request.csv = array.toString();