計算2個時間間隔之間的時間差 - 邏輯問題

Question

我有一個字符串，時間如下;

NSString *time = "06.45 pm"; 

我需要假設這個時間是今天的日期，然後得到當前系統時間，並計算兩者之間的時間差。

我該怎麼做？

注：以上時間不指定date，（只有時間給出）

Answer 1

NSString *time = @"06.45 pm"; 

NSDate *date1; 
NSDate *date2; 
{ 
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init]; 
    [formatter setDateFormat:@"hh.mm a"]; 
    date1 = [formatter dateFromString:time]; 
    date2 = [formatter dateFromString:[formatter stringFromDate:[NSDate date]]]; 
    [formatter release]; 
} 
NSTimeInterval interval = [date1 timeIntervalSinceDate: date2];//[date1 timeIntervalSince1970] - [date2 timeIntervalSince1970]; 
int hour = interval/3600; 
int minute = (int)interval % 3600/60; 

NSLog(@"%@ %dh %dm", interval<0?@"-":@"+", ABS(hour), ABS(minute)); 

Answer 2

確保當你這樣做，你使用的是日曆的操作，使得考慮到時間更改（夏時制，閏秒等）：

NSString *time = @"06.45 pm"; 
NSCalendar *cal = [NSCalendar currentCalendar]; 
NSDate  *today = [NSDate date]; 

NSDateFormatter *formatter = [[NSDateFormatter alloc] init]; 
[formatter setDateFormat:@"hh.mm a"]; 

// Convert time to a NSDate and break it down into hours, minutes, and seconds: 
NSDate   *timeAsDate = [formatter dateFromString:time]; 
NSDateComponents *timeComps = [cal components:NSHourCalendarUnit | 
               NSMinuteCalendarUnit | 
               NSSecondCalendarUnit 
             fromDate:timeAsDate]; 

// Take today's date and add "time" to it: 
NSDateComponents *comps = [cal components:NSYearCalendarUnit | 
              NSMonthCalendarUnit | 
              NSDayCalendarUnit 
            fromDate:today]; 
comps.hour    = timeComps.hour; 
comps.minute    = timeComps.minute; 
comps.second    = timeComps.second; 
NSDate *timeOnTodaysDate = [cal dateFromComponents:comps]; 

// Now calculate the difference: 
NSTimeInterval difference = [today timeIntervalSinceDate:timeOnTodaysDate];