计算iOS中给定时间点之前的时间
我想知道现在与下周三 14:00 之间的秒差。
我发现 [NSDate date]; 为我提供了当前时间和日期，并且 NSTimeInterval 通常用于此目的（我想使用这个间隔在其他地方，而其他地方需要 NSTimeInterval），因此代码如下所示：
NSDate *now = [NSDate date];
NSDate *nextWednesday = ???;
// profit
NSTimeInterval secondsUntilNextWednesday = [nextWednesday timeIntervalSinceDate:now];
但是如何获取下周三的日期？
Edit2：我改进了这个方法，我仍然很不喜欢它，但这是一个巨大的改进。而且，这更让人想起我的伪尝试。
- (NSTimeInterval)secondsUntilNextWednesday
{
NSCalendar *calendar = [NSCalendar currentCalendar];
NSDate *today = [NSDate date];
NSDateComponents *components = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit) fromDate: today];
// 17 == 15:00, seemingly. (timezones)
[components setHour:17];
[components setWeekday:4];
NSDate *wednesday = [calendar dateFromComponents:components];
NSTimeInterval secondsToWednesday = [wednesday timeIntervalSinceDate:today];
// if secondsToWednesday is negative, it has already been wednesday, 15:00 (or 16:00 depending on DST)
if (secondsToWednesday < 0)
{
secondsToWednesday += 604800;
}
return secondsToWednesday;
}
I want to know the difference in seconds between now and, say, the next wednesday, 14:00.
I have found that [NSDate date]; gives me the current time and date, and that an NSTimeInterval would typically be used for this purpose (and I would like to use this interval somewhere else, and the somewhere else wants an NSTimeInterval), so the code would look like this:
NSDate *now = [NSDate date];
NSDate *nextWednesday = ???;
// profit
NSTimeInterval secondsUntilNextWednesday = [nextWednesday timeIntervalSinceDate:now];
But how do I get the date of next wednesday?
Edit2: I sort of improved the method, I still pretty much don't like it, but it's a huge improvement. Also, it's much more reminiscent of my pseudo-attempt.
- (NSTimeInterval)secondsUntilNextWednesday
{
NSCalendar *calendar = [NSCalendar currentCalendar];
NSDate *today = [NSDate date];
NSDateComponents *components = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit) fromDate: today];
// 17 == 15:00, seemingly. (timezones)
[components setHour:17];
[components setWeekday:4];
NSDate *wednesday = [calendar dateFromComponents:components];
NSTimeInterval secondsToWednesday = [wednesday timeIntervalSinceDate:today];
// if secondsToWednesday is negative, it has already been wednesday, 15:00 (or 16:00 depending on DST)
if (secondsToWednesday < 0)
{
secondsToWednesday += 604800;
}
return secondsToWednesday;
}
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Apple 提供了一个方便的指南，其中包含您需要了解的有关日期的所有信息： 日期和时间编程指南
您可能想查看一下
NSDateComponents和NSCalendar类。请参阅日历、日期组件和日历单位 >指南中的从组件创建日期中的示例基于不同的已知日期组件创建日期。
例如，该指南还展示了如何根据日期组件计算相对于当前日期的下一个星期三。
Apple provides a handy guide with all you need to know about dates: the Date and Time Programming Guide
You probably want to take a look at the classes
NSDateComponentsandNSCalendar.See Calendars, Date Components, and Calendar Units > Creating a Date from Components in the guide for an example to create a date based on different known date components.
The guide also shows how to calculate based on date components to get to the next wednesday relative to the current date for example.