IOS--时间 NSDate,NSTimeInterval的一些转换

 //1.时间格式
 NSDateFormatter *_dateFormatter = [[NSDateFormatter alloc] init];
 [_dateFormatter setDateFormat:@"YYYY年MM月dd天hh小时mm分ss秒"];
 
 //2.获取系统时间
 NSString *date = [_dateFormatter stringFromDate:[NSDate date]];
 
 //3.NSDate转化为时间戳
 NSTimeInterval a=[date timeIntervalSince1970];
 
 //4.时间戳转化为NSDate
 NSDate *stampDate = [NSDate dateWithTimeIntervalSince1970:timeInter];
 
 //4.NSDate转化为NSString
 NSString* dateString = [_dateFormatter stringFromDate:date];
 
 //5.传入时间差,重置格式
 //传入时间差,转换格式
 - (NSString *)timeWithMessageString:(NSTimeInterval)timeInter
 {
     
     int month = timeInter / (3600 * 24 * 30);
     int day = timeInter / (3600 * 24);
     int hour = timeInter / 3600;
     int minute = timeInter / 60;
     
     int day_process = day - month * 30;
     int hour_process = hour - day *24;
     int minute_process = minute - hour *60;
     int miao_process = timeInter - minute*60;
     
     NSString *timedate = nil;
     if (day == 0) {
         timedate = [NSString stringWithFormat:@"%d小时%d分%d秒",hour_process,minute_process,miao_process];
         if (hour == 0) {
            timedate = [NSString stringWithFormat:@"%d分%d秒",minute_process,miao_process];
             if (hour == 0) {
                 timedate = [NSString stringWithFormat:@"%d秒",miao_process];
             }
         }
     }else{
         timedate = [NSString stringWithFormat:@"%d天%d小时%d分%d秒",day_process,hour_process,minute_process,miao_process];
     }
     
     
     timedate = [NSString stringWithFormat:@"限时优惠: 还剩%@",timedate];
     return timedate;
 }

//当前时间的半小时后
NSDate *date1 = [NSDate date];
 NSDate *date2 = [[NSDate date] dateByAddingTimeInterval: 30*60];
    NSDate *date3 = [NSDate dateWithTimeIntervalSinceNow:30*60];