確定給定日期（加或減DST班次小時數）的小時數

Question

給定NSDate和NSCalendar，如何確定指定日期之後當天的小時數。取決於下一天是進入夏令時（23），正常（24）還是現在的夏令時（25），這將是23,24或25。

Answer 1

你可以問日曆中的任意單元有多長（和單位開始時）與rangeOfUnit:startDate:interval:forDate:。

// Test date (the day DST begins) 
NSDateComponents *components = [[NSDateComponents alloc] init]; 
components.year = 2012; 
components.month = 3; 
components.day = 11; 

NSCalendar *calendar = [NSCalendar currentCalendar]; 
NSDate *date = [calendar dateFromComponents:components]; 
NSTimeInterval dayLength; 
[calendar rangeOfUnit:NSDayCalendarUnit startDate:NULL interval:&dayLength forDate:date]; 
NSLog(@"%f seconds", dayLength); 

注意rangeOfUnit:...可以techincally失敗並返回NO，但如果控制不應該是能夠發生的輸入。

Answer 2

// Test input 
NSDateFormatter *formatter = [[NSDateFormatter alloc] init]; 
formatter.dateFormat = @"yyyy MM dd HH:mm:ss"; 
NSDate *referenceDate = [formatter dateFromString:@"2012 03 24 13:14:14"]; 

// Get reference date with day precision 
NSCalendar *calendar = [NSCalendar currentCalendar]; 
unsigned unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit; 
NSDateComponents *components = [calendar components:unitFlags fromDate:referenceDate]; 

NSDate *today = [calendar dateFromComponents:components]; 

// Set components to add 1 day 
components = [[NSDateComponents alloc] init]; 
components.day = 1; 

// The day after the reference date 
NSDate *tomorrow = [calendar dateByAddingComponents:components toDate:today options:0]; 

// The day after that 
NSDate *afterTomorrow = [calendar dateByAddingComponents:components toDate:tomorrow options:0]; 

// Difference in hours: 23, 24 or 25 
NSUInteger hours = [afterTomorrow timeIntervalSinceDate:tomorrow]/3600;