Programmactic Access DataGrid Rows and Columns

Question

Hello,
I am new to ActionScript. Can you tell me how can I access
the rows and columns of a data grid?
What I want to do is that when the application load, I will
populate the datagrid with the Xml returned from the webservice.
After that, webservice will be called periodically (using timer)
and the information in the datagrid needs to be updated. The cells
which are updated need to be highlighted.
The datagrid actually contains the stock market data (symbol
name and its other attributes). So once the datagrid has been
populated on application creation, it contains all the symbols in
the market. After that, only attributes of the symbols will change,
like price, volume etc. What I want is that once the datagrid is
populated, i can access the row by using the value of symbol code
and then update the appropriate columns of that symbol. (Xml from
next time will contain only symbols whose values change from last
time).
Below is the code that I have written so far.
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="
http://www.adobe.com/2006/mxml"
layout="absolute"
creationComplete="OnAppCreationComplete()" width="100%"
height="100%">
<mx:Script>
<![CDATA[
import mx.rpc.events.ResultEvent;
private var count:uint = 0;
private var messageFramXmlList:XMLList;
private var marketSnapshotTimer:Timer = new Timer(1000);
private function OnAppCreationComplete() : void
this.ajaxServiceInvokerProxy.addEventListener(ResultEvent.RESULT,
this.OnWebServiceResultArrived);
this.ajaxServiceInvokerProxy.InvokeService.send();
this.marketSnapshotTimer.addEventListener(TimerEvent.TIMER,
this.OnSnapshotTimerTick);
this.marketSnapshotTimer.start();
private function
OnWebServiceResultArrived(event:ResultEvent) : void
var marketSnapshotXml:XML = new XML(event.result);
this.messageFramXmlList =
marketSnapshotXml.child("MarketSnapshot").child("MessageFrameList")[0].child("MessageFram e");
this.dgTopPosts.dataProvider = this.messageFramXmlList;
this.btnCounter.label = this.count.toString();
private function OnSnapshotTimerTick(event:TimerEvent) :
void
this.count++;
this.ajaxServiceInvokerProxy.InvokeService.send();
]]>
</mx:Script>
<mx:WebService id="ajaxServiceInvokerProxy"
wsdl="
http://jehanzeb/ajaxserviceinvoker/ajaxserviceinvoker.asmx?wsdl"
useProxy="false">
<mx:operation name="InvokeService">
<mx:request>
<serviceWithComonentName>DetailedSnapshotComponent.MarketSnapshot@TADAWUL</serviceWithCom onentName>
<parametersXml><![CDATA[ <Parameters/>
]]></parametersXml>
</mx:request>
</mx:operation>
</mx:WebService>
<mx:Panel x="10" y="10" width="100%" height="100%"
layout="absolute" title="Market View">
<mx:RichTextEditor id="txtMarketViewResult" x="10" y="10"
width="612" height="194" />
<mx:DataGrid x="10" y="223" id="dgTopPosts" width="100%"
height="303">
<mx:columns>
<mx:DataGridColumn headerText="Symbol Code"
dataField="SymbolID" />
<mx:DataGridColumn headerText="Last Time"
dataField="LastTime" />
<mx:DataGridColumn headerText="Net Change"
dataField="NetChange" width="75"
/>
<mx:DataGridColumn headerText="Percent Change"
dataField="PercentChange" width="75" />
<mx:DataGridColumn headerText="Previous Closed"
dataField="PreviousClosed" width="75"/>
<mx:DataGridColumn headerText="Close" dataField="Close"
width="75"/>
<mx:DataGridColumn headerText="Direction"
dataField="Direction" width="75"/>
<mx:DataGridColumn headerText="BidPrice"
dataField="BidPrice" width="75"/>
<mx:DataGridColumn headerText="AskPrice"
dataField="AskPrice" width="75"/>
<mx:DataGridColumn headerText="BidVolume"
dataField="BidVolume" width="75"/>
<mx:DataGridColumn headerText="AskVolume"
dataField="AskVolume" width="75"/>
</mx:columns>
</mx:DataGrid>
<mx:LinkButton id="btnCounter" x="10" y="528" width="306"
textAlign="left" label="" />
</mx:Panel>
</mx:Application>

Answer 1

To achieve what you want, I would have two functions:
* One populates the DataGrid for the first time, i.e. the
inital load
* The other does the 'update' on each interval, since there's
logic required
To update the DataGrid with only the rows that have changed,
you're going to have to compare
the incoming XML to the existing XML in the dataProvider of
the DataGrid, then selectively update the dataProvider.
You can use the
getItemAt() and
setItemAt() methods of the data provider to check each row
against the incoming data. So, some example code:
// This is the function which handles the result of your
'updated data only' webservice
private function handleUpdateInvoke (event:ResultEvent) :
void {
var incoming:XML = new XML(event.result);
var someList:XMLList = incoming.somePattern;
// For each data provider item, check the key and if it
matches
// one of the incoming keys, update it at that index
var numRows = this.dgTopPosts.dataProvider.length;
var existingDataRow:*
for (var i:Number = 0; i < numRows; i++) {
existingDataRow = this.dgTopPosts.dataProvider.getItemAt(i);
for each (var newDataRow:* in someList) {
if (existingDataRow.SymbolID == newDataRow.SymbolID) {
this.dgTopPosts.dataProvider.setItemAt(newDataRow, i);
}