Display NSDates in terms of week - ios

Question

Scenario:
I have an expense tracking iOS Application and I am storing expenses from a expense detail view controller into a table view (with fetched results controller) that shows the list of expenses along with the category and amount and date. I do have a date attribute in my entity "Money" which is a parent entity for either an expense or an income.
Question:
What I want is to basically categorize my expenses for a given week, a month, or year and display it as the section header title for example : (Oct 1- Oct 7, 2012) and it shows expenses amount and related stuff according to that particular week. Two buttons are provided in that view, if I would press the right button, it will increment the week by a week (Oct 1- Oct 7, 2012 now shows Oct8 - Oct 15, 2012) and similarly the left button would decrement the week by a week.
How would I accomplish that? I am trying the following code - doesn't work.
- (void)weekCalculation
{
NSDate *today = [NSDate date]; // present date (current date)
NSCalendar* calendar = [NSCalendar currentCalendar];
NSDateComponents* comps = [calendar components:NSYearForWeekOfYearCalendarUnit |NSYearCalendarUnit|NSMonthCalendarUnit|NSWeekCalendarUnit|NSWeekdayCalendarUnit fromDate:today];
[comps setWeekday:1]; // 1: Sunday
firstDateOfTheWeek = [[calendar dateFromComponents:comps] retain];
[comps setWeekday:7]; // 7: Saturday
lastDateOfTheWeek = [[calendar dateFromComponents:comps] retain];
NSLog(#" first date of week =%#", firstDateOfTheWeek);
NSLog(#" last date of week =%#", lastDateOfTheWeek);
firstDateOfWeek = [dateFormatter stringFromDate:firstDateOfTheWeek];
lastDateOfWeek = [dateFormatter stringFromDate:lastDateOfTheWeek];
}
Code for incrementing date -
- (IBAction)showNextDates:(id)sender
{
int addDaysCount = 7;
NSDateComponents *dateComponents = [[[NSDateComponents alloc] init] autorelease];
[dateComponents setDay:addDaysCount];
NSDate *newDate1 = [[NSCalendar currentCalendar]
dateByAddingComponents:dateComponents
toDate:firstDateOfTheWeek options:0];
NSDate *newDate2 = [[NSCalendar currentCalendar]
dateByAddingComponents:dateComponents
toDate:lastDateOfTheWeek options:0];
NSLog(#" new dates =%# %#", newDate1, newDate2);
}
Suppose the week shows like this (Nov4, 2012 - Nov10, 2012) and I press the increment button, I see in the console, date changes to Nov11,2012 and Nov.17, 2012 which is right but if I press the increment button again, it shows the same date again (Nov 11, 2012 and Nov.17, 2012).
Please help me out here.

Answer 1

Declare currentDate as an #property in your class. And try this.
#property(nonatomic, retain) NSDate *currentDate;
Initially set
self.currentDate = [NSDate date];
before calling this method.
- (void)weekCalculation
{
NSCalendar* calendar = [NSCalendar currentCalendar];
NSDateComponents* comps = [calendar components:NSYearForWeekOfYearCalendarUnit |NSYearCalendarUnit|NSMonthCalendarUnit|NSWeekCalendarUnit|NSWeekdayCalendarUnit fromDate:self.currentDate];
[comps setWeekday:1]; // 1: Sunday
firstDateOfTheWeek = [[calendar dateFromComponents:comps] retain];
[comps setWeekday:7]; // 7: Saturday
lastDateOfTheWeek = [[calendar dateFromComponents:comps] retain];
NSLog(#" first date of week =%#", firstDateOfTheWeek);
NSLog(#" last date of week =%#", lastDateOfTheWeek);
firstDateOfWeek = [dateFormatter stringFromDate:firstDateOfTheWeek];
lastDateOfWeek = [dateFormatter stringFromDate:lastDateOfTheWeek];
}
Once the view is loaded self.currentDate value should be updated from showNextDates. Make sure it is not getting reset anywhere else.
- (IBAction)showNextDates:(id)sender
{
int addDaysCount = 7;
NSDateComponents *dateComponents = [[[NSDateComponents alloc] init] autorelease];
[dateComponents setDay:addDaysCount];
NSDate *newDate1 = [[NSCalendar currentCalendar]
dateByAddingComponents:dateComponents
toDate:firstDateOfTheWeek options:0];
NSDate *newDate2 = [[NSCalendar currentCalendar]
dateByAddingComponents:dateComponents
toDate:lastDateOfTheWeek options:0];
NSLog(#" new dates =%# %#", newDate1, newDate2);
self.currentDate = newDate1;
}

Answer 2

I had needed similar thing in one of my old projects and achieved it via the code below. It sets this weeks date to an NSDate variable and adds/removes 7 days from day component in each button click. Here is the code:
NSCalendar *calendar = [NSCalendar currentCalendar];
[calendar setTimeZone:[NSTimeZone timeZoneWithAbbreviation:#"GMT"]];
NSDate *date = [NSDate date];
NSDateComponents *components = [calendar components:(NSYearCalendarUnit|NSWeekdayCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit) fromDate:date ];
//
[components setDay:([components day] - ([components weekday] )+2)];
self.currentDate = [calendar dateFromComponents:components];
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
formatter.dateFormat = #"dd.MM.yyyy HH:mm:ss";
self.datelabel.text = [formatter stringFromDate:self.currentDate];
The code above calculates this week start and sets it to currentDate variable. I Have two UIButtons with UIActions named prevClick and nextClick which calls the method that sets the next or previous weekstart:
- (IBAction)prevClick:(id)sender {
[self addRemoveWeek:NO];
}
-(void)addRemoveWeek:(BOOL)add{
NSCalendar *calendar = [NSCalendar currentCalendar];
[calendar setTimeZone:[NSTimeZone timeZoneWithAbbreviation:#"GMT"]];
NSDateComponents *components = [calendar components:(NSYearCalendarUnit|NSWeekdayCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit) fromDate:self.currentDate ];
components.day = add?components.day+7:components.day-7;
self.currentDate = [calendar dateFromComponents:components];
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
formatter.dateFormat = #"dd.MM.yyyy HH:mm:ss";
self.datelabel.text = [formatter stringFromDate:self.currentDate];
}
- (IBAction)nextClk:(id)sender {
[self addRemoveWeek: YES];
}