两个NSDate之间的小时差异

Question

在这里,我试图计算两个日期之间的小时数.当我运行应用程序时,它崩溃了.你能告诉我这段代码中的错误吗？

NSString *lastViewedString = @"2012-04-25 06:13:21 +0000";
NSDateFormatter *dateFormatter = [[[NSDateFormatter alloc] init] autorelease];
[dateFormatter setDateFormat: @"yyyy-MM-dd HH:mm:ss zzz"];

NSDate *lastViewed = [[dateFormatter dateFromString:lastViewedString] retain];
NSDate *now = [NSDate date];

NSLog(@"lastViewed: %@", lastViewed); //2012-04-25 06:13:21 +0000
NSLog(@"now: %@", now); //2012-04-25 07:00:30 +0000

NSTimeInterval distanceBetweenDates = [now timeIntervalSinceDate:lastViewed];
double secondsInAnHour = 3600;
NSInteger hoursBetweenDates = distanceBetweenDates / secondsInAnHour;

NSLog(@"hoursBetweenDates: %@", hoursBetweenDates);

Answer 1

参考这个大致相似的问题的答案,更好和Apple认可的方式是使用这样的NSCalendar方法:

- (NSInteger)hoursBetween:(NSDate *)firstDate and:(NSDate *)secondDate {
   NSUInteger unitFlags = NSCalendarUnitHour;
   NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
   NSDateComponents *components = [calendar components:unitFlags fromDate:firstDate toDate:secondDate options:0];
   return [components hour]+1;
}

如果您使用NSCalendarIdentifierGregorian的是iOS 8或更高版本,请使用而不是弃用NSGregorianCalendar.

Answer 2

我认为差异应该是int值...

NSLog(@"hoursBetweenDates: %d", hoursBetweenDates);

希望对你有帮助..