easy way to add tooltip on datagrid Items in Flex

import mx.collections.ArrayCollection; // this holds the grid data
[Bindable]
private var myData:ArrayCollection = new ArrayCollection();
private function doInit():void{
myData.addItem({fname:"Joe",lname:"Bloggs"});
myData.addItem({fname:"Joe1",lname:"Bloggs"});
}

private function buildToolTip(item:Object):String{
var myString:String = "";
if(item != null)
{
myString = myString + "Firstname : " + item.fname + "\n";
myString = myString + "Lastname : " + item.lname + "\n"
}
return myString;
}
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