得到一排tableview

Question

点击按钮时如何获得indexPath.row？这是我现在的代码：

let alert = SCLAlertView()
let txt = alert.addTextField("Quantity")
txt.keyboardType = UIKeyboardType.NumberPad
txt.text = "\(1)"

alert.addButton("Add to cart") {
    var sar:Cart!
    let indexPath = self.tableView?.indexPathForSelectedRow
    print("\(indexPath.row)")
}

但它不起作用。