dateByAddingTimeInterval參數語法

Question

如果我發送方法dateByAddingTimeInterval：到NSDate的，象下面這樣：

NSDate *today = [NSDate date]; 
NSDate *tomorrow = [now dateByAddingTimeInterval:24.0]; 
NSDate *yesterday = [now dateByAddingTimeInterval:-24.0]; 

NSArray *dates = [NSArray arrayWithObjects: today, tomorrow, yesterday, nil]; 

NSLog(@"today's date is %@", [dates objectAtIndex:0]); 
NSLog(@"yesterday's date was %@", [dates objectAtIndex:2]); 

我得到這樣的輸出：

...The first date is 2012-08-30 02:14:19 +0000 
...The third date is 2012-08-30 02:13:55 +0000 

這很奇怪，因爲第三日期應該是2012- 08-29

但是...如果我將NSDate消息更改爲：

NSDate *today = [NSDate date]; 
NSDate *tomorrow = [now dateByAddingTimeInterval:24.0 * 60.0 * 60.0]; 
NSDate *yesterday = [now dateByAddingTimeInterval:-24.0 * 60.0 * 60.0]; 

爲什麼加入* 60.0 ...

...The first date is 2012-08-30 02:15:25 +0000 
...The third date is 2012-08-29 02:15:25 +0000 

使輸出是否正確？

謝謝。

Answer 1

NSDate按秒計算時間。