獲取本月每個NSDate作爲NSString

Question

在我的應用程序中，我需要爲每個月的每一天存儲一個URL。從今天開始倒退。我會怎麼做？

到目前爲止沒有問題得到今天的NSDate作爲的NSString：

NSDate* date = [NSDate date]; 
NSDateFormatter* format = [[[NSDateFormatter alloc]init]autorelease]; 
[format setDateFormat:@"yyyyMdd"]; 

NSString* str = [format stringFromDate:date]; 

所以我怎麼會去，例如，如果我想在一個字符串的日期，可以說，17天前？

PS。我想要使​​用這些日期並將它們存儲在一個字符串中，以獲取過去一個月中每天的網址，例如www.myurl.com/pictureYEAR-MONTH-DAY.jpg

Answer 1

這與Alex的答案，但它看起來像他只得到天從本月開始到哪一天這是今天。這裏是你如何能在本月拿到所有的日子：

NSDate *today = [NSDate date]; 
NSCalendar *cal = [NSCalendar currentCalendar]; 

NSMutableArray *datesThisMonth = [NSMutableArray array]; 
NSRange rangeOfDaysThisMonth = [cal rangeOfUnit:NSDayCalendarUnit inUnit:NSMonthCalendarUnit forDate:today]; 

NSDateComponents *components = [cal components:(NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit | NSEraCalendarUnit) fromDate:today]; 
[components setHour:0]; 
[components setMinute:0]; 
[components setSecond:0]; 

for (NSInteger i = rangeOfDaysThisMonth.location; i < NSMaxRange(rangeOfDaysThisMonth); ++i) { 
    [components setDay:i]; 
    NSDate *dayInMonth = [cal dateFromComponents:components]; 
    [datesThisMonth addObject:dayInMonth]; 
} 

這將留下與NSDates的NSArray，並在當月每天一個日期。

---

如果你想這是「11天以前」的日期，你可以做到這一點很容易得：

NSCalendar *cal = [NSCalendar currentCalendar]; 
NSDate *today = [NSDate date]; 
NSDateComponents *diff = [[NSDateComponents alloc] init]; 
[diff setDay:-17]; 

NSDate *seventeenDaysAgo = [cal dateByAddingComponents:diff toDate:today]; 

---

一旦你有一個NSDate，這是很簡單的把它變成一串：

NSDateFormatter *formatter = [[NSDateFormatter alloc] init]; 
[formatter setDateFormat:@"yyyy-MM-dd"]; 

NSDate *date = ...; 
NSString *string = [formatter stringFromDate:date]; 

Answer 2

只需獲取當前日期的NSDateComponents ，然後從中提取一天，然後寫一個for循環，直到你達到1，每次從組件中創建一個新的日期，並將其存儲爲一個字符串。

代碼大概可以說以上的話那麼在這裏你去（測試）：

NSMutableArray *dates = [[NSMutableArray alloc] init]; 
NSDateFormatter *fmt = [[NSDateFormatter alloc] init]; 
[fmt setDateFormat:@"yyyy-MM-dd"]; // you can set this to whatever you like 
NSDate *today = [NSDate date]; // get todays date 
NSCalendar *cal = [NSCalendar currentCalendar]; // needed to work with components 
NSDateComponents *components = [cal components:(NSDayCalendarUnit|NSMonthCalendarUnit|NSYearCalendarUnit) fromDate:today]; 
NSUInteger day = [components day]; 
for (NSUInteger i=day; i>0; i--) { 
    // loop through all days till down to 1 
    [components setDay:i]; // update the day in the components 
    NSDate *date = [cal dateFromComponents:components]; 
    [dates addObject:[fmt stringFromDate:date]]; // add the new date 
} 

for (NSString *date in dates) { 
    NSString *str = [NSString stringWithFormat:@"www.myurl.com/picture/%@",date]; 
    NSLog(@"%@",str); // voila, your URL. 
} 

[fmt release]; 
[dates release];