Help with NSUserDefaults and Dates

Question

Hi,
In my application I have an NSDatePicker that shows all adjustment of only time, the picker is bound to an NSUserDefaults key named 'time'.
How do I go about parsing the the time from the user defaults and comparing it to the current time and returning true if they are the same (to minutes not seconds) and false if they are not the same?
I have searched through the code of a few open applications and can't determine what code I need to make it work. I'm guessing I need to make use of 'objectForKey:' and the NSDate class but I need some help getting started.
Thanks,
Alex

Answer 1

First, you need to get the time object from the NSUserDefaults.
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NSDate *d_time = (NSDate *) [[NSUserDefaults standardUserDefaults] objectForKey:@"time"];
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Next, you need the current date.
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NSDate *d_now = [NSDate date];
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Finally, to compare the two. NSDate's isEqualToDate: message is not good enough if you need to compare dates to the second, as it compares to the millisecond (which would result in NO a lot of times). compare: compares pointers; it won't work. You use the timeIntervalSinceDate: function, which returns NSTimeInterval, a typedef to double that is exact to the second. We compare the result to zero to see if they are the same time.
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if (![d_time timeIntervalSinceDate:d_now])
do_something();
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We use the ! operator so that the zero value of NSTimeInterval (no seconds in between) is interpreted as TRUE.
Here is a message that does it all:
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- (BOOL)timeIsNow
NSDate *d_then;
d_then = (NSDate *) [[NSUserDefaults sharedUserDefaults] objectForKey:@"time";
return ![d_then timeIntervalSinceDate:[NSDate date]];
===
Message was edited by: andlabs
Message was edited by: andlabs