1.獲取當前時間
+(NSString *)getCurrentDate
{
    //獲取當前時間
    NSDate *now = [NSDate date];
    KELog(@"now date is: %@", now);
    
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSUInteger unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
    NSDateComponents *dateComponent = [calendar components:unitFlags fromDate:now];
    
    NSInteger year = [dateComponent year];
    NSInteger month = [dateComponent month];
    NSInteger day = [dateComponent day];
    NSInteger hour = [dateComponent hour];
    NSInteger minute = [dateComponent minute];
    NSInteger second = [dateComponent second];
    NSString * currentDate = [NSString stringWithFormat:@"%ld-%.2ld-%.2ld %.2ld:%.2ld:%.2ld",year,month,day,hour,minute,second];
    
    return currentDate;

}

2.NSDate轉換成時間戳
       
        NSDate *datenow = [NSDate date];//現在時間,你可以輸出來看下是什麼格式
       
        NSString *timeSp = [NSString stringWithFormat:@"%d", (long)[datenow timeIntervalSince1970]];

        NSLog(@"timeSp:%@",timeSp); //時間戳的值時間戳轉時間的方法

//NSString 轉 NSDate
+(NSDate *)dateWithString:(NSString *)dataString
{
    NSDateFormatter * format = [[NSDateFormatter alloc] init];
    
    [format setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    
    NSDate * date = [format dateFromString:[self getCurrentDate]];
    
    return date;
}

//NSDate 轉 NSString
+(NSString *)stringWithDate:(NSDate *)date{
    
    NSDateFormatter * dateFormatter = [[NSDateFormatter alloc] init];
    
    [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    
    NSString*strDate = [dateFormatter stringFromDate:[NSDate date]];
    
    NSLog(@"%@",strDate);
    
    [dateFormatter release];
    
    return strDate;
}