兩個NSDate之間的小時差異

Question

在這里，我試圖計算兩個日期之間的小時數。 當我運行應用程序時，它崩潰了。 你能告訴我這段代碼中的錯誤嗎？

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

參考這個大致相似的問題的答案，更好和Apple認可的方式是使用這樣的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;
}

如果您的目標是iOS 8或更高版本，請使用NSCalendarIdentifierGregorian而不是棄用的NSGregorianCalendar 。

Answer 2

我認為差異應該是int值...

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

希望這個能對您有所幫助..

Answer 3

無法使用NSInteger顯示

NSLog(@"%@", hoursBetweenDates);

改為使用：

NSLog(@"%d", hoursBetweenDates); 

如果不確定使用Apple Developer Docs中的內容： http ： //developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/Strings/Articles/formatSpecifiers.html#//apple_ref/doc/uid/TP40004265