How change UIImageView in external screen on background mode - ios

Question

I need show changes in external screen with UIImageView when my ios app is on background mode.
I use this code to change the UIImageView
campaingTimer = [NSTimer scheduledTimerWithTimeInterval:timeFirstAd target:self selector:#selector(changeImage) userInfo:nil repeats:NO];
This works when my app is active, but when in background, enters the changeImage method, but not change the picture.

Answer 1

NSTimer selectors are not guaranteed to fire off in the background. Unless you're registering for specific permissions, such as playing music in the background, and whatever you're actually doing in the background is directly related to the permission you asked for, you should work under the assumption you will not be able to execute code while the app is backgrounded, as that'll set you up to succeed much better than trying to find workarounds.
In this scenario, it seems like you want to change the image after so much time passes. That NSTimer you have (assuming your methods are written correctly) will work while the app is in the foreground, but to deal with background I recommend listening for the appDidEnterBackground and appWillEnterForeground and posting notifications (see sample code below).
AppDelegate.m
================
- (void)applicationDidEnterBackground:(UIApplication *)application
{
self.currentTime = [NSDate date];
}
- (void)applicationWillEnterForeground:(UIApplication *)application
{
[[NSNotificationCenter defaultCenter] postNotificationName:kNotificationNameForBecameActive object:nil userInfo:#{kUserInfoForBecameActive: self.currentTime}];
}
================
ViewController.m
================
- (void)viewDidLoad
{
[super viewDidLoad];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(didBecomeActive:) name:kNotificationNameForBecameActive object:nil];
}
- (void)didBecomeActive:(NSNotification *)notification
{
NSDate *sleepDate = notification.userInfo[kUserInfoForBecameActive];
NSTimeInterval secondsPassed = [[NSDate date] timeIntervalSinceDate:sleepDate];
if (secondsPassed >= timeFirstAd)
{
[self changeImage];
}
// reinitialize NSTimer
}
================
Alternatively, you could post notifications for both appDidEnterBackground and appWillEnterForeground and save the time there, along with invalidating your NSTimer and restarting it.