Handling event listeners - returns from async queries...

Question

i'm a longtime programmer, but relatively new to async calls.
so i think i'm missing something basic...
when my current flex screen loads, it performs three queries
to pre-populate the screen. first query is the "header" record,
second query gets the "line item" records, and the third query gets
values for a picklist which will be in the data grid. (note that
i'm querying a web service - although i doubt that matters much...)
when each query is finished and the local objects
(ArrayCollections, etc) are populated, i want to perform a specific
action. So my first thought is to write three
"handle*QueryComplete" methods, and add an event listener to the
connection before each query. So these three lines will appear in
my code:
apex.addEventListener(QueryEvent.QUERY_EVENT,
handleHeaderQueryCompleted);
apex.addEventListener(QueryEvent.QUERY_EVENT,
handleLineItemQueryCompleted);
apex.addEventListener(QueryEvent.QUERY_EVENT,
handleProdQueryCompleted);
But then when one qeury finishes, it will call all three
handle* methods, right? How am I supposed to do this so that when
each query completes, it performs the proper action?
thanks for your time
chris

Answer 1

In order to identify a result with its call, to perform some
specific processing, you can use the AsyncToken. Below is some
sample code.
Tracy
Sample code using HTTPService, e4x, handler function to
populate a list item.
Also shows usage of AsyncToken.
The DataGrid tag:
<mx:DataGrid id="dg" dataProvider="{_xlcMyListData}"
.../>
The HTTPService tag:
<mx:HTTPService id="service" resultFormat="e4x"
result="onResult(event)" fault="..../>
Script block declaration:
import mx.rpc.Events.ResultEvent;
[Bindable]private var _xlcMyListData:XMLListCollection;
Invoke send:
var oRequest:Object = new Object();
oRequest.Arg1 = "value1";
var callToken:AsyncToken = service.send(oRequest);
token.callId = "myQuery1";
Result Handler function:
private function onResult(oEvent:ResultEvent):void {
var xmlResult:XML = XML(event.result); //converts result
Object to XML. can also use "as" operator
var xlMyListData:XMLList = xmlResult.myListData; //depends
on xml format, is row data
_xlcMyListData = new XMLListCollection(xlMyListData); //wrap
the XMLList in a collection
trace(_xlcMyListData.toXMLString()); //so you can see
exactly how to specify dataField or build labelFunction
var callToken:AsyncToken = oEvent.token;
var sCallId = callToken.callId; //"myQuery1"
switch(sCallId) { //Process the result conditionally
case "myQuery1":
doQuery2(); //do whatever. this example calls another data
service query
break;
}//onResult