Swift

DateHelper

extension String {
    func toDate(format: String) -> NSDate? {
        let dateFormatter = NSDateFormatter()
        dateFormatter.dateFormat = format
        return dateFormatter.dateFromString(self)
    }
}

extension NSDate {
    func toString(format: String) -> String {
        let dateFormatter = NSDateFormatter()
        dateFormatter.dateFormat = format
        return dateFormatter.stringFromDate(self)
    }
}


var a = "17:23"
var d = a.toDate("HH:mm")
d.toString("yyyy-MM-dd HH:mm")