Use the updateDataChild() method to add a label to a single data point on the line
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<!-- charts/UpdateDataChildExample.mxml -->
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:mx="library://ns.adobe.com/flex/mx" xmlns:s="library://ns.adobe.com/flex/spark"
height="600">
<fx:Script>
import mx.controls.Label;
import mx.charts.chartClasses.CartesianCanvasValue;
import mx.collections.ArrayCollection;
[Bindable]
public var expenses:ArrayCollection = new ArrayCollection([
{Month:"Jan", Profit:2000, Expenses:1500, Amount:450},
{Month:"Feb", Profit:1000, Expenses:200, Amount:600},
{Month:"Mar", Profit:1500, Expenses:500, Amount:300}
]);
public function drawData():void
{
canvas.clear();
canvas.beginFill(0xFF0033, 1);
canvas.drawCircle("Feb", 1000, 20);
canvas.endFill();
var myLabel:Label = new Label();
myLabel.text = "X";
myLabel.setStyle("fontWeight", "bold");
myLabel.setStyle("fontSize", 20);
canvas.addChild(myLabel);
canvas.updateDataChild(myLabel, "Feb", 1100);
}
</fx:Script>
<s:layout>
<s:VerticalLayout />
</s:layout>
<s:Panel title="Line Chart">
<s:layout>
<s:HorizontalLayout />
</s:layout>
<mx:LineChart id="myChart" dataProvider="{expenses}"
showDataTips="true" creationComplete="drawData()">
<mx:annotationElements>
<mx:CartesianDataCanvas id="canvas"
includeInRanges="true" />
</mx:annotationElements>
<mx:horizontalAxis>
<mx:CategoryAxis dataProvider="{expenses}"
categoryField="Month" />
</mx:horizontalAxis>
<mx:series>
<mx:LineSeries yField="Profit" displayName="Profit" />
<mx:LineSeries yField="Expenses" displayName="Expenses" />
</mx:series>
</mx:LineChart>
<mx:Legend dataProvider="{myChart}" />
</s:Panel>
</s:Application>
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