iOS app runs for only 1 second in background - ios

Question

I have 2 classes, ViewController class, and Worker. All the code that I need to run in the background is in the Worker class.
My ViewController looks something like this:
- (void)viewDidLoad {
//create an instance of 'Worker'
}
- buttonClick {
//call the 'manager' method in the worker instance that was just created (do this method as a background thread)
}
My Worker class looks something like this:
- (void)manager {
//call 'repeat' method as a background thread
}
- (void)repeat {
//call 'innerWorker' method as a background thread
}
- (void)innerWorker {
//do work
}
The repeat method needs to get run every second.
I've tried the 2 following ways to make the repeat method run every second.
Method 1 :
timerObj = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:#selector(repeatMethod) userInfo:nil repeats:YES];
Method 2:
Putting this code at the end of repeat:
dispatch_queue_t q_background = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);
double delayInSeconds = 1.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
dispatch_after(popTime, q_background, ^(void){
[self repeatMethod];
});
Both of these 2 methods work fine as long as the app is in the foreground but the moment I press the home button, the repeat method runs one last time, but does not call the innerWorker method and then the app is suspended. I know this by using NSLogs all over the place.
I realize Method 2 is a bit of a hack but that's fine as this is an internal app that I wont be publishing.
All the methods are called as background threads using this code: eg:
dispatch_queue_t q_background = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);
dispatch_async(q_background, ^{
[self repeatMethod];
});
I'm new to iOS so maybe I'm missing something small here. I just want my app to keep running in the background. Please help me.

Answer 1

First of all: the dispatch_queue priority has nothing to do with running in background ... it is the priority in the queue.
Here are the info:
DISPATCH_QUEUE_PRIORITY_HIGH Items dispatched to the queue will run at high priority, i.e. the queue will be scheduled for execution before any default priority or low priority queue.
DISPATCH_QUEUE_PRIORITY_DEFAULT Items dispatched to the queue will run at the default priority, i.e. the queue will be scheduled for execution after all high priority queues have been scheduled, but before any low priority queues have been scheduled.
DISPATCH_QUEUE_PRIORITY_LOW Items dispatched to the queue will run at low priority, i.e. the queue will be scheduled for execution after all default priority and high priority queues have been scheduled.
DISPATCH_QUEUE_PRIORITY_BACKGROUND Items dispatched to the queue will run at background priority, i.e. the queue will be scheduled for execution after all higher priority queues have been scheduled and the system will run items on this queue on a thread with background status as per setpriority(2) (i.e. disk I/O is throttled and the thread's scheduling priority is set to lowest value).
For "real" background operations check this:
https://developer.apple.com/library/ios/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/BackgroundExecution/BackgroundExecution.html
The answer to your question depends on what you want to do.

Answer 2

Only the following types of apps, with the appropriate plist flag set, can execute a background process while the app is still in the foreground:
Apps that play audible content to the user while in the background,
such as a music player app
Apps that record audio content while in the background
Apps that keep users informed of their location at all times, such
as a navigation app
Apps that support Voice over Internet Protocol (VoIP)
Apps that need to download and process new content regularly
Apps that receive regular updates from external accessories
If your app falls outside of one of those categories, and will go through app store approval, you will need to devise another strategy for doing the background work you desire to preform.
More info can be found here:
https://developer.apple.com/library/ios/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/BackgroundExecution/BackgroundExecution.html#//apple_ref/doc/uid/TP40007072-CH4-SW3