ios how to change an image at specific time - objective-c

Question

I have an image that i want to display as a sun during daytime i.e. from 6am to 6pm, and moon from 6pm to 6am.
I have successfully implemented that but the problem is the image would not change when it reaches the specified time unless re-run the apps before the image change itself.
I don't want to use NSTimer to check the time, like every second. The only possible solution i think of is using NSLocalNotification but I'm a newbiew to it. any help? =)
-(void) dayOrNight
{
NSDate* date = [NSDate date];
NSDateFormatter* dateFormat = [[NSDateFormatter alloc]init];
[dateFormat setDateFormat:#"HHmm"];
NSString* dateString = [dateFormat stringFromDate:date];
NSNumber* currentTime = [NSNumber numberWithInt:[dateString intValue]];
NSNumber* daytime = [NSNumber numberWithInt:600];
NSNumber* nightime = [NSNumber numberWithInt:1800];
NSLog(#"current time: %#",dateString);
dayNight = [[UIImageView alloc] initWithFrame:CGRectMake(265, 10, 50, 50)];
if ( [currentTime doubleValue] >= [daytime doubleValue] && [currentTime doubleValue] <= [nightime doubleValue] )
{
dayNight.image = [UIImage imageNamed:#"Sun.png"];
}
else
{
dayNight.image = [UIImage imageNamed:#"moon.png"];
}
[self.view addSubview:dayNight];
}

Answer 1

Local notification should be fine, I guess.
Here you can get all needed code snippets to implement execution of dayOrNight method at needed time. Also, you shouldn't add new view every time you change the picture.

Answer 2

I think it is impossible to do without NSTimer. U can set refreshTime by yourself (for example 1 min/ if u don`t want to do it every second)))
Or u can call this method in other methods, which are working in your class every time...
maybe u have some object, which u use during your class is working...
-(IBAction)myButtonWhichIPressDuringIworkHere {
///some actions
[self dayOrNight];
}
In other case you should to use NSTimer

Answer 3

you don't need to check the time at every second.
this is one of the possible solutions. it has been tested on real device only.
your UIYourViewController.m
- (void)viewWillAppear:(BOOL)animated {
NSDate *_currentDate = [NSDate date];
NSDateFormatter *_dateFormatter = [[NSDateFormatter alloc] init];
[_dateFormatter setDateFormat:#"yyyy-MM-dd' 06:00AM +0000'"]; // set the morning date here
NSString *_morningDateString = [_dateFormatter stringFromDate:_currentDate];
[_dateFormatter setDateFormat:#"yyyy-MM-dd' 06:00PM +0000'"]; // set the evening date here
NSString *_eveningDateString = [_dateFormatter stringFromDate:_currentDate];
[_dateFormatter setDateFormat:#"yyyy-MM-dd hh:mma zzz"];
NSDate *_morningDate = [_dateFormatter dateFromString:_morningDateString];
NSDate *_eveningDate = [_dateFormatter dateFromString:_eveningDateString];
NSTimeInterval _intervalToMorningDate = [_morningDate timeIntervalSinceDate:_currentDate];
NSTimeInterval _intervalToEveningDate = [_eveningDate timeIntervalSinceDate:_currentDate];
if (_intervalToMorningDate > 0) {
// now it is night
dayNight.image = [UIImage imageNamed:#"moon.png"];
[self performSelector:#selector(replaceTheBackgoundForMorning) withObject:nil afterDelay:_intervalToMorningDate];
} else {
// now it is daytime
dayNight.image = [UIImage imageNamed:#"Sun.png"];
[self performSelector:#selector(replaceTheBackgoundForEvening) withObject:nil afterDelay:_intervalToEveningDate];
}
}
- (void)viewDidDisappear:(BOOL)animated {
[NSObject cancelPreviousPerformRequestsWithTarget:self];
}
and finally you should add them to your same .m file:
-(void)replaceTheBackgoundForMorning {
// reaplce the backgound here
dayNight.image = [UIImage imageNamed:#"Sun.png"];
}
- (void)replaceTheBackgoundForEvening {
// reaplce the backgoung here
dayNight.image = [UIImage imageNamed:#"moon.png"];
}