小笔记

var dateFormatter = NSDateFormatter();
dateFormatter.dateFormat = ""; //时间格式，参考 ："yyyy'-'MM'-'dd'T'HH':'mm':'ss'Z'"
于是就可以：
dateFormatter.stringFromDate( NSDate 的值，比如 datePicker.date )
简易方法： 
func dateformatterDate(date: NSDate) -> NSString
{
var dateFormatter: NSDateFormatterNSDateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "MM-dd-yyyy"
dateFormatter.timeZone = NSTimeZone(abbreviation: "UTC")

return dateFormatter.stringFromDate(date)


}

//--- Convert Date String to NSDate ---//

func dateformatterDateString(dateString: NSString) -> NSDate?
{
var dateFormatter: NSDateFormatterNSDateFormatter = NSDateFormatter()
dateFormatter.dateFormat = "MM-dd-yyyy"
dateFormatter.timeZone = NSTimeZone(abbreviation: "UTC")


return dateFormatter.dateFromString(dateString)
}