这就是我想要做的，当我单击button时，我想跳到顶部，但是当我单击button时，我的应用程序崩溃了。

@IBaction func addToCart(_ sender: UIButton) {

    if quantitylbl.text == "0" {
        dismiss(animated: true)
    }

    // Save in to userdefault
    let section = sender.tag / 100
    let row = sender.tag % 100
    let dict = arrayCategory[section] as? NSDictionary
    let subLimit = getStringValueFromAPIValue(apiValue: dict?.value(forKey: "limit"),defaultvalue: "")

    let cell = self.tableView.cellForRow(at: IndexPath(row: row,section: section)) as! CustomizationDropDownTableViewCell

    if self.section_quantity[section] < Int(truncating: subLimit.numberValue!) {
        cell.btnDropdown.becomeFirstResponder()
    }
}