Unable to cast object of type System.Web.UI.WebControls.GridViewRow to type System.Web.UI.WebCont

please tell me how to convert datagrid to gridview

Dim ddllist As DropDownList = CType(sender, DropDownList)
Dim cell As TableCell = CType(ddllist.Parent, TableCell)
Dim item As DataGridItem = CType(cell.Parent, DataGridItem)
Dim ddlType As DropDownList = CType(item.Cells(0).FindControl("cmbShowName"), DropDownList)