倒计时

原始版本

仅贴出计算时间的核心代码

//每个时间间隔0.1s调用一次
func secondsToTimeString(seconds: Float) -> (String, Int, Int, Int, Int, Int) {
    
    let temp = seconds
    let seconds = Int(temp)
    
    // 天数计算
    let days = (seconds)/(24*3600);
    //小时计算
    let hours = (seconds)%(24*3600)/3600;
    //分钟计算
    let minutes = (seconds)%3600/60;
    //秒计算
    let second = (seconds)%60;
    let timeString  = String(format: "%lu天 %02lu:%02lu:%02lu", days, hours, minutes, second)
    return (timeString, days, hours, minutes, second, Int((temp-Float(seconds))*10))
}

每次调用都需要重新计算时分秒，计算很频繁。CPU这样也太累了吧？于是我决定给它减减负。实际上大多数时间有些数字都不会变动。比如分钟60秒才会变一次，小时60分钟才会变一次。等等。

进化版本

定义如下属性：
var days: Int?;

//小时
var hours: Int?;
var hoursFlag: Bool = false

//分钟
var minutes: Int?
var minutesFlag: Bool = false

//秒
var second: Int?;
var secondFlag: Bool = false

//每个时间间隔0.1s调用一次
func secondsToTimeString2(seconds: Float) -> (Int, Int, Int, Int, Int) {
    let temp = seconds
    let seconds = Int(temp)
    let minInterval = Int((temp-Float(seconds))*10)
    if second == nil {
        second = (seconds)%60
    }
    if minutes == nil {
        minutes = (seconds)%3600/60
    }
    if hours == nil {
        hours = (seconds)%(24*3600)/3600
    }
    if days == nil {
        days = (seconds)/(24*3600)
        return (days!, hours!, minutes!, second!, minInterval)
    }
    if minInterval == 9  {
        secondFlag = true
        if second == 0 {
            second = 60
            second! -= 1
        } else {
            second! -= 1
        }
    }
    if second == 59 && secondFlag == true {
        secondFlag = false
        minutesFlag = true
        if minutes == 0 {
            minutes = 60
            minutes! -= 1
        } else {
            minutes! -= 1
        }
    }
    if minutes == 59 && minutesFlag == true {
        minutesFlag = false
        hoursFlag = true
        if hours == 0 {
            hours = 24
            hours! -= 1
        } else {
            hours! -= 1
        }
    }
    if hours == 23 && hoursFlag == true {
        hoursFlag = false
        if days != 0 {
            days! -= 1
        }
    }
    return (days!, hours!, minutes!, second!, minInterval)
}

代码变得复杂多了，你们觉得我是不是咸的蛋疼？哈哈哈，我就是这样追求极致的呀！
代码虽然多了很多，也花了我不少时间debug。但是改进后性能却提升了很多。