我想用swift语言写一个BMI程序.
在Objective-C中,我可以这样做:
double myDouble = [myString doubleValue];
但我怎样才能用迅捷的语言做到这一点呢?
我想用swift语言写一个BMI程序.
在Objective-C中,我可以这样做:
double myDouble = [myString doubleValue];
但我怎样才能用迅捷的语言做到这一点呢?
Swift 4.2+ String to Double
应该使用新的类型初始值设定项在字符串和数字类型(双精度、浮点、Int)之间进行转换.它将返回一个可选类型(Double?)如果字符串不是数字,则将具有正确的值或nil.
Note:不建议使用NSString doubleValue属性,因为如果无法转换该值(即:用户输入错误),它将返回0.
let lessPrecisePI = Float("3.14")
let morePrecisePI = Double("3.1415926536")
let invalidNumber = Float("alphabet") // nil, not a valid number
Unwrap the values to use them using if/let
if let cost = Double(textField.text!) {
print("The user entered a value price of \(cost)")
} else {
print("Not a valid number: \(textField.text!)")
}
您可以使用NumberFormatter
类转换格式化的数字和货币.
let formatter = NumberFormatter()
formatter.locale = Locale.current // USA: Locale(identifier: "en_US")
formatter.numberStyle = .decimal
let number = formatter.number(from: "9,999.99")
Currency formats
let usLocale = Locale(identifier: "en_US")
let frenchLocale = Locale(identifier: "fr_FR")
let germanLocale = Locale(identifier: "de_DE")
let englishUKLocale = Locale(identifier: "en_GB") // United Kingdom
formatter.numberStyle = .currency
formatter.locale = usLocale
let usCurrency = formatter.number(from: "$9,999.99")
formatter.locale = frenchLocale
let frenchCurrency = formatter.number(from: "9999,99€")
// Note: "9 999,99€" fails with grouping separator
// Note: "9999,99 €" fails with a space before the €
formatter.locale = germanLocale
let germanCurrency = formatter.number(from: "9999,99€")
// Note: "9.999,99€" fails with grouping separator
formatter.locale = englishUKLocale
let englishUKCurrency = formatter.number(from: "£9,999.99")
阅读更多关于我的blog post about converting String to Double types (and currency).