It look like what I thought was going to be something simple, has
turned out to be less so and fraught with danger programatically.
I was just thinking though, would it be easier just to covert the
weekday value into seconds (weekday * 60 * 60 * 24) and subtract that
from the current date? This would save you from the issue of year and
month boundaries. Following code is untested (written in Mail):
NSDateComponents *components = [[NSDateComponents alloc] init];
NSDate *startOfTheWeek;
NSDate *now = [NSDate date];
components = [calendar components:NSWeekdayCalendarUnit fromDate:now];
startOfTheWeek = [now addTimeInterval:-([components weekday] * 60 *
60 * 24)];
NSLog(@"The start of the week is %@", startOfTheWeek);
JJ
On 02/07/2008, at 4:37 AM, mmalc crawford wrote:
On Jul 1, 2008, at 10:44 AM, Chris Kane wrote:
My apologies; I did do some testing and found that the resultant
date was always correct.
Could you elaborate on what circumstances this might not be correct?
Did you try starting with a starting date of Jan 1, 2009? The
Weekday would be 5, the Day 1.
Rats, no; I tried the dates at the beginning of 2008, 2003, and
1999...
The previous Sunday is December 28, 2008.
... although, hmm, yes, that's the result I get(*). Nevertheless...
Passing a Year, Month, Day of (2009, 1, -3) (-3 == 1 - (5 - 1) in
your original computation) is passing an out-of-bounds value with
dateWithComponents:, with who-knows-what effect. It might be well-
defined, it might not be. The result might change between OS
releases. In other words, it seems a bit ambiguous, so best to
just avoid it.
... point taken. I'll update the documentation accordingly.
mmalc
(*)
NSDateComponents *components = [[NSDateComponents alloc] init];
[components setYear:2009];
[components setMonth:1];
[components setDay:1];
NSDate *testDate = [gregorian dateFromComponents:comps];
[components release];
NSDateComponents *components = [gregorian
components:NSWeekdayCalendarUnit | NSYearCalendarUnit |
NSMonthCalendarUnit | NSDayCalendarUnit fromDate:testDate];
NSLog(@"day: %d, weekDay: %d, delta: %d", [components day],
[components weekday], [components day] - [components weekday]);
// day: 1, weekDay: 5, delta: -4
[components setDay:([components day] - ([components weekday] -
1))];
[components setWeekday:NSUndefinedDateComponent];
NSDate *beginningOfWeek = [gregorian
dateFromComponents:components];
NSLog(@"beginningOfWeek: %@", beginningOfWeek);
// beginningOfWeek: 2008-12-28 00:00:00 -0800
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