How to update a UILabel once per day - ios

Question

I have a UILabel that randomly will show text from a list I have provided.
I want the UILabel to show one item per day.
What's the best way to handle this?
Should I use an NSTimer or is there a different method?
I'm not worried about a specific time of the day, just that the UILabel updates once per day.
Thank you!

Answer 1

One option would be to save the current date into NSUserDefaults when you show the label.
When your view controller is loaded you get that date from NSUserDefaults. If the difference between the saved date and "now" is more than 24 hours you update the label (and save the new date), otherwise show the current label.
You probably also want the view controller to listen for the "will enter foreground" notification. Each time your app returns to the foreground you will want to do the same check.

Answer 2

Store the date in preferences, and compare when the app comes into the foreground. Your appDelegate would look something like this:
- (void)applicationDidEnterBackground:(UIApplication *)application
{
NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
[prefs setObject:[NSDate date] forKey:#"savedDate"];
[prefs synchronize];
}
- (void)applicationDidBecomeActive:(UIApplication *)application
{
NSDate *savedDate = [[NSUserDefaults standardUserDefaults] objectForKey:#"savedDate"];
NSDateComponents *dateComponents = [[NSCalendar currentCalendar] components:NSCalendarUnitDay fromDate:savedDate toDate:[NSDate date] options:0];
if ([dateComponents day] >= 1) {
[[NSNotificationCenter defaultCenter] postNotificationName:#"updateLabel" object:nil];
}
}
Then in your view controller, listen for the notification:
-(void) viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(updateLabel) name:#"updateLabel" object:nil];
}
-(void) viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated];
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
-(void) updateLabel {
//update your label here
}
For updating at midnight, check out UIApplicationSignificantTimeChangeNotification. There is a relevant answer here: https://stackoverflow.com/a/15537806/1144632