Finding Textbox control inside datagrid in WPF Application.

string message = "";
POSLibrary.Entity.Supplier supplier = new POSLibrary.Entity.Supplier();
POSLibrary.Entity.SupplierList supplierlist = new POSLibrary.Entity.SupplierList();
supplierlist.SupplierID = SupplierID;
string msg="";
DataTable dtSupplierItemsList = new DataTable();
var retValue = suppliers.SearchSupplierList(supplierlist, out msg, out dtSupplierItemsList);
var itemsSource = grdItems.ItemsSource as IEnumerable;


if (grdItems.Items.Count > 0)
{
for (int i = 0; i < grdItems.SelectedItems.Count; i++)
{
System.Data.DataRowView row = (System.Data.DataRowView)grdItems.SelectedItems[i];
int itemID = Convert.ToInt16(row.Row.ItemArray[0].ToString());
int supplierID = SupplierID;
if (retValue)
{
int dtsupplierID = 0;
int dtitemID = 0;
for (int j = 0; j <\; dtSupplierItemsList.Rows.Count; j++)
{
dtitemID = Convert.ToInt16(dtSupplierItemsList.Rows[j].ItemArray[1].ToString());
dtsupplierID = Convert.ToInt16(dtSupplierItemsList.Rows[j].ItemArray[2].ToString());
if (itemID == dtitemID && supplierID == dtsupplierID)
{

object o = grdItems.Items;
DataGridRow lvi = (DataGridRow)grdItems.ItemContainerGenerator.ContainerFromItem(o);
TextBox txtcost = FindByName("txtcost", lvi) as TextBox; //here lvi is coming null and i have to find this textbox
string cost = dtSupplierItemsList.Rows[j].ItemArray[4].ToString();
string minimumOrder = dtSupplierItemsList.Rows[j].ItemArray[3].ToString();
}
}
}
}
}

here the calling function

private FrameworkElement FindByName(string name, FrameworkElement root)
{
Stack<FrameworkElement> tree = new Stack<FrameworkElement>();
tree.Push(root);
while (tree.Count > 0)
{
FrameworkElement current = tree.Pop(); // root is null
if (current.Name == name)
return current;

int count = VisualTreeHelper.GetChildrenCount(current);
for (int SupplierCounter = 0; SupplierCounter < count; ++SupplierCounter)
{
DependencyObject child = VisualTreeHelper.GetChild(current, SupplierCounter);
if (child is FrameworkElement)
tree.Push((FrameworkElement)child);
}
}
return null;
}