ios 学习笔记 —— NSDate 使用详解（一）

NSTimeInterval secondsPerDay = 24*60*60;
NSTimeInterval secondsPerHour = 60*60;
//现在(今天)
NSDate *date1 = [NSDate date];
NSDate *date2 = [NSDate dateWithTimeIntervalSinceNow:secondsPerDay];
NSDate *date3 = [NSDate dateWithTimeIntervalSinceNow:secondsPerDay*2];
//昨天
NSDate *date4 = [date1 addTimeInterval:-secondsPerDay];
//前天
NSDate *date5 = [date1 addTimeInterval:-secondsPerDay*2];
//前一小时
NSDate *date6 = [date1 addTimeInterval:-secondsPerHour];