有一个需求获取当天的0点 做分界线, 然后去获取步数的数据的, 发现都是oc的,

就转了下swift版本的
`

extension NSDate{
/// 当前的0 点 0分 0 秒时间
var currentDayzeroOfDate:NSDate{

    let calendar:NSCalendar = NSCalendar.currentCalendar()
    //calendar.components(NSCalendarUnit(), fromDate: self)//UIntMax
    
    let unitFlags: NSCalendarUnit = [
        
        NSCalendarUnit.Year,
        NSCalendarUnit.Month,
        NSCalendarUnit.Day,
        .Hour,
        .Minute,
        .Second ]
    
    //calendar.components(unitFlags, fromDate: self)//解析当前的时间 返回NSDateComponents 解析后的数据后面设置解析后的时间在反转
    let components = calendar.components(unitFlags, fromDate: self)//NSDateComponents() 不初始化, 直接返回解析的时间

    components.hour = 0
    components.minute = 0
    components.second = 0
    print(" 2  \(components.year)  \(components.month)  \(components.day) \( components.hour)")
    let date = calendar.dateFromComponents(components)

    return date!
}

}
`