Loading XML at run-time using the mx:HTTPService tag

In the previous post we looked at how to load an XML document in at compile-time and have it embedded in our Flex application. But that technique really only works if the XML data in question never changes. What if you had an XML document that was constantly changing on a daily, or hourly, basis. For example, consider an RSS reader application. If the XML was loaded and embedded in the XML document at compile-time, the RSS would never get updated. And while that may be good in some cases (such as a kiosk, or somewhere without an internet connection where you wanted to display static information), in many cases it may not work.
So, lets take a look at using the mx:HTTPService tag to dynamically load an XML file.
The following example dynamically loads an XML file at run-time using the mx:HTTPService tag, rather than using mx:XML and grabbing the data at compile-time:

<?xml version="1.0" encoding="UTF-8" standalone="no" ? ><FLVCoreCuePoints version="1" >
<CuePoint > <Time >0</Time > <Type >event</Type > <Name >slide1</Name > <Parameters > <Parameter > <Name >id</Name > <Value >value</Value > </Parameter > </Parameters > </CuePoint >
<CuePoint > <Time >5000</Time > <Type >event</Type > <Name >slide2</Name > <Parameters > <Parameter > <Name >param1</Name > <Value >value1</Value > </Parameter > <Parameter > <Name >param2</Name > <Value >value2</Value > </Parameter > </Parameters > </CuePoint >
<CuePoint > <Time >20000</Time > <Type >event</Type > <Name >slide3</Name > </CuePoint >
</FLVCoreCuePoints ><?xml version="1.0" encoding="utf-8"? ><mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="vertical" verticalAlign="top" backgroundColor="white" creationComplete="tempXML.send();" >
<mx:HTTPService id="tempXML" url="xml/cuePoints.xml" resultFormat="e4x" / > <mx:XMLListCollection id="cuePointXMLList" source="{tempXML.lastResult.CuePoint}" / > <mx:XMLListCollection id="parametersXMLList" source="{dataGrid.selectedItem.Parameters.Parameter}" / >
<mx:Script > <![CDATA[ private function parametersLabelFunction(item:Object, column:DataGridColumn):String { return item.Parameters.Parameter.length(); }
private function numericSortCompareFunction(objA:Object, objB:Object):int { var itemA:Number = parseInt(objA.Time.text()) as Number; var itemB:Number = parseInt(objB.Time.text()) as Number;
if (itemA > itemB) { return 1; } else if (itemA < itemB) { return -1; } else { return 0; } } ]] > </mx:Script >
<mx:VBox >
<mx:DataGrid id="dataGrid" dataProvider="{cuePointXMLList}" width="100%" rowCount="{cuePointXMLList.length + 1}" > <mx:columns > <mx:DataGridColumn id="timeCol" dataField="Time" headerText="Time (ms):" sortCompareFunction="numericSortCompareFunction" / > <mx:DataGridColumn id="typeCol" dataField="Type" headerText="Type:" / > <mx:DataGridColumn id="nameCol" dataField="Name" headerText="Name:" / > <mx:DataGridColumn id="parametersCol" dataField="Parameters" headerText="Parameters:" labelFunction="parametersLabelFunction" / > </mx:columns > </mx:DataGrid >
<mx:DataGrid id="parametersDataGrid" dataProvider="{parametersXMLList}" width="100%" visible="{parametersXMLList.length > 0}" rowCount="{parametersXMLList.length + 1}" > <mx:columns > <mx:DataGridColumn id="parameterNameCol" dataField="Name" headerText="Parameter Name:" / > <mx:DataGridColumn id="parameterValueCol" dataField="Value" headerText="Parameter Value:" / > </mx:columns > </mx:DataGrid >
</mx:VBox >
</mx:Application >The first thing you notice is that the code is nearly identical to the previous example which used mx:XML. The subtle differences are that instead of mx:XML we used mx:HTTPService to get the data. Also, we now listen for the creationComplete event for on the Application tag where we trigger the XML loading using the HTTPService.send() method. Finally, the locations of the files changed slightly. Now instead of the XML being calculated relative to the MXML file, the XML gets placed relative to the generated SWF file. All the other code stayed the same.