self.tableView.scrollToRow(at: IndexPath.init(row: 0, section: 0), at: .top, animated: true)
self.tb.scrollRectToVisible(CGRect(x: 0, y: 48, self.tb.frame.size.width, height: self.tb.frame.size.width), animated: true)
String(format : "%.0f%@", floor(sender.value), "%")// 如果要显示%，需要格式化%@
isNaN//A Boolean value indicating whether the instance is NaN (“not a number”).
string.components(separatedBy: CharacterSet(charactersIn:"0123456789").inverted).joined(separator: "")//Returns an array containing substrings from the string that have been divided by characters in the given set.
NumberFormatter().number(from: self.returnAmountField().text!)// by parsing string using the receiver’s format, or nil if no single number could be parsed.