swift - 将参数传递给方法时出现错误 "extra argument in call"

Question

我正在尝试用 swift 编写以下 Objective-C 代码:

NSCalendar *cal = [NSCalendar currentCalendar];
NSDate *now = [NSDate date];
NSDate *startOfTheWeek;
NSTimeInterval interval;
[cal rangeOfUnit:NSWeekCalendarUnit 
       startDate:&startOfTheWeek 
        interval:&interval 
         forDate:now];

它将本周的开始写入 startOfTheWeek 并将周持续时间写入 interval。

我在 Playground 上写作

let now:NSDate = NSDate()
var startDate:NSDate
var duration: NSTimeInterval // also tried "var duration: CMutablePointer<NSTimeInterval>"
let cal = NSCalendar.currentCalendar()
cal.rangeOfUnit(unit: NSCalendarUnit.WeekCalendarUnit, startDate: startDate, interval: duration, forDate: now)"

虽然代码完成告诉我签名是

cal.rangeOfUnit(<#unit: NSCalendarUnit#>, startDate: AutoreleasingUnsafePointer<NSDate?>, interval: <#CMutablePointer<NSTimeInterval>#>, forDate: <#NSDate?#>)

发生错误说 Extra argument 'interval' in call

我做错了什么？

我也试过

cal.rangeOfUnit(NSCalendarUnit.WeekCalendarUnit, startDate: startDate, interval: duration, forDate: now)

但这会产生错误

"could not find an overload for 'rangeOfUnit' that accepts the supplied arguments."

Answer 1

试试这个:

let now = NSDate()
var startDate: NSDate? = nil
var duration: NSTimeInterval = 0
let cal = NSCalendar.currentCalendar()

cal.rangeOfUnit(NSCalendarUnit.WeekCalendarUnit, startDate: &startDate,
    interval: &duration, forDate: now)

(默认情况下，第一个参数没有外部名称，因此不应命名。)