ios - 我应该使用 NSDate 来跟踪到达时间和迟到时间吗？

Question

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Answer 1

如果您只是比较持续时间，NSTimeInterval是适合您的类型(它实际上是 float 毫秒数，向读者解释其意图)。

NSDate对于需要以实际时钟时间开始或结束的计算是必需的。

编辑 根据描述的更具体的问题:给定用户的日常工作开始时间，计算与到达工作时间的偏差，关键计算涉及 NSDate .

它旨在回答以下问题:与实际时钟相比，用户现在是否准时？此计算的关键参数是当前时间 NSDate以及用户计划到达时间NSDate可以保存为简单标量并通过 NSDateComponents 转换为 NSDate ...

// core location triggered an arrival notification and we call this
// assumes a "User" class that knows user state, like the time user is due at work
-(void)userJustArrived:(User *)myUser {
    NSDate *now = [NSDate date];
    NSDate *dueAtWork = [myUser dueAtWork];
    NSTimeInterval lateness = [now timeIntervalSinceDate:dueAtWork];

    // a negative lateness means user is early
    if (lateness > 0)
        NSLog(@"you are %f milliseconds late.  perhaps you should go into standup comedy", lateness);
}

// on the user class, due at work produces an NSDate from what you would
// have stored earlier as the time when a user is expected at work
- (NSDate *)dueAtWork {
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSDateComponents *components = [calendar components:(NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay) fromDate:[NSDate date]];
    // these are given as user state, the user's planned start time
    components.hour = self.dueAtWorkHour;
    components.minute = self.dueAtWorkMinute;
    return [components date];
}