calculate textbox value on FpSpread on leave event

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ASP.NET4

I am using spread.net spread sheet

My user enter value in a column of sheet

and there is a textbox also where i calculate all record calculation.

I am not getting a way how to update textbox.

private void SetFormula_Circular()
    {
        string[] strArr = new string[FpSpread1.ActiveSheetView.RowCount];
        string[] strArrsumAC = new string[FpSpread1.ActiveSheetView.RowCount];
        for (int i = 0; i < FpSpread1.ActiveSheetView.RowCount; i++)
        {
            if (!string.IsNullOrEmpty(FpSpread1.ActiveSheetView.Cells[i, 7].Text))
                strArr[i] = FpSpread1.ActiveSheetView.Cells[i, 7].Text;
            if (!string.IsNullOrEmpty(FpSpread1.ActiveSheetView.Cells[i, 8].Text))
                strArrsumAC[i] = FpSpread1.ActiveSheetView.Cells[i, 8].Text.Replace("$","");
        }
        decimal sumForecast_Cost = 0;
        for (int j = 0; j < strArr.Length; j++)
        {
            sumForecast_Cost = sumForecast_Cost + Convert.ToDecimal(strArr[j]);
        }
        txtProjectedCost.Text = Convert.ToString(sumForecast_Cost);
        decimal sumActualCost = 0;
        for (int j = 0; j < strArrsumAC.Length; j++)
        {
            sumActualCost = sumActualCost + Convert.ToDecimal(strArrsumAC[j]);
        }
        txtActualCost.Text = Convert.ToString(sumActualCost);
    }

right now i am using this way.but it is not working