Swift版获取月份的最后一天

    //这个月的最后一天
    func getLastDay(var year:Int,var month:Int) -> Int?{
        var dateFormatter:NSDateFormatter = NSDateFormatter();
        dateFormatter.dateFormat = "yyyy/MM/dd";
        if month == 12 {
            month = 0
            year++
        }
        var targetDate:NSDate? = dateFormatter.dateFromString(String(format:"%04d/%02d/01",year,month+1));
        if targetDate != nil {
            
            var orgDate = NSDate(timeInterval:(24*60*60)*(-1), sinceDate: targetDate!)
            var str:String = dateFormatter.stringFromDate(orgDate)
            
            return str.lastPathComponent.toInt();
        }
        
        return nil;
    }