Iphone 如何获取当前时间和第二天设置时间之间的时差？

我设计了一个应用程序，在其中发送推送通知。该通知根据时间间隔生成。该时间间隔根据当前时间和第二天选定时间的差值计算。所以我遇到了一个问题，那就是我如何为接下来的几天设定我想要设定的时间？第二个问题是如何获得它们之间的差异？

下面是获取时间间隔到明天某个时间的代码：

NSCalendar *calendar = [NSCalendar currentCalendar];

// Get today date
NSDateComponents *components = [calendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit fromDate:[NSDate date]];

// Set the time tomorrow
components.hour = 12;
components.minute = 30;
components.day = components.day + 1;

NSDate *tomorrow = [calendar dateFromComponents:components];
NSLog(@"tomorrow: %@", tomorrow);

NSTimeInterval timeTillTomorrow = [tomorrow timeIntervalSinceNow];
NSLog(@"timeTillTomorrow: %.0f seconds", timeTillTomorrow);

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下面是将时间间隔设置为明天某个时间的代码：

NSCalendar *calendar = [NSCalendar currentCalendar];

// Get today date
NSDateComponents *components = [calendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit fromDate:[NSDate date]];

// Set the time tomorrow
components.hour = 12;
components.minute = 30;
components.day = components.day + 1;

NSDate *tomorrow = [calendar dateFromComponents:components];
NSLog(@"tomorrow: %@", tomorrow);

NSTimeInterval timeTillTomorrow = [tomorrow timeIntervalSinceNow];
NSLog(@"timeTillTomorrow: %.0f seconds", timeTillTomorrow);