Background and NSThread - ios

Question

I'm trying to understand how the NSThread is working when the app is going to the background. I have the following code in appdeligate:
- (void)applicationDidEnterBackground:(UIApplication *)application
{
[self backgroundHandler];
}
- (void)backgroundHandler {
NSInteger counter=0;int scontinue=true;
while(scontinue){
NSLog(#"counter:%d",counter++);
sleep(1)
}
}
When I go to the background then it prints out every 1second a value. I have kept it open for about 5min and it gave me:
counter:1
counter:2
...
counter:300
And this keeps going. However if try to get into the foreground the backgroundHandler doesn't exit the while loop and my app doesn't respond to anything.
Now I change the applicationDideEnterBackground and instead I'm using a thread, i.e.
- (void)applicationDidEnterBackground:(UIApplication *)application
{
[NSThread detachNewThreadSelector:#selector(backgroundHandler) toTarget:self withObject:nil];
}
- (void)backgroundHandler {
NSInteger counter=0;int scontinue=true;
while(scontinue){
NSLog(#"counter:%d",counter++);
//sleep(1) : I remove the sleep for the shake of the example
}
}
Although I was expecting to have the same behaviour as in the previous case the thread seems to be hold after some ms. So what I had as a result is:
counter:1
counter:2
...
counter:30
And now the thread stucks at that point without executing anything. When I go to the foreground then the thread starts running again, i.e. counter increases and it is being printed out. The application runs again normally.
The above example is a rather simplistic version of what I'm tyring to do. What I actually want is when by app goes to the background to communicate with a server as long as the user doesn't go to the foreground. When it goes any communication should be terminated. So what I actually want is a combination of the simple examples above, i.e. when go to background in while loop keep asking the server, and when I enter to the foreground my app start responding normally and terminate the the backgroundHandler for loop.
Any help?

Answer 1

The main purpose of - (void)applicationDidEnterBackground:(UIApplication *)application is to save the state of the application when the application goes into background. In this if the application starts using a lot of the CPU or RAM, OS will terminate the app based on the state of the phone.
When you want to perform background operations or services to the server enable the background fetch by calling [[UIApplication sharedApplication] setMinimumBackgroundFetchInterval:UIApplicationBackgroundFetchIntervalMinimum]; in - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions of the AppDelegate.
-(void)application:(UIApplication *)application performFetchWithCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler
{
//Add your code here
[self setBackgroundCheckInterval:UIBackgroundFetchResultNewData];
completionHandler(UIBackgroundFetchResultNewData);
}
- (void)setBackgroundCheckInterval:(NSInteger)resultCode
{
UIBackgroundRefreshStatus status = [UIApplication sharedApplication].backgroundRefreshStatus;
if (status == UIBackgroundRefreshStatusAvailable)
{
switch (resultCode)
{
case UIBackgroundFetchResultFailed :
[[UIApplication sharedApplication] setMinimumBackgroundFetchInterval:BACKGROUND_CHECK_INTERVAL_NO_NEW_DATA];
break;
case UIBackgroundFetchResultNewData :
[[UIApplication sharedApplication] setMinimumBackgroundFetchInterval:BACKGROUND_CHECK_INTERVAL_NEW_DATA];
break;
case UIBackgroundFetchResultNoData :
[[UIApplication sharedApplication] setMinimumBackgroundFetchInterval:BACKGROUND_CHECK_INTERVAL_NO_NEW_DATA];
break;
}
}
}