[flexcoders] Null Return when try to get total of sum from one field

[Harry Saputra]

I try this :

.mxml file :

...
<mx:DataGridColumn id="sks" headerText="SKS"  width="20" dataField="sks"/>
...
<mx:Button x="685" y="10" label="Button" click="showTotalDataTranskrip()"/>
...

.as file :

[Bindable]
Public var lengthArrDataTranksrip:int;
public var total:Number;

        public function totalDataTranskrip(col:DataGridColumn):String
        {
                
                lengthArrDataTranksrip = arrDataTranskrip.length; //
arrDataTranskrip is DataProvider as Array
                
                for (var i:int = 0; i < lengthArrDataTranksrip; i++)
                {       
                total = total + Number(arrDataTranskrip[i][col.dataField]);
                }
                
                return String(total);
                
        }
        
        public function showTotalDataTranskrip():void
        {
                txtTotalSKS.text = totalDataTranskrip(sks);
        }


I get Null Return...please help me to solve this problem, thanks :)