Check network connection in background and upload data - ios

Question

I get a requirement to be able to check if there is data with fail status and upload them via webservice.
The flow is gonna be:
User try to upload data but fail because of no internet connection
User stops using app, so the app goes background
Apps start to identify whether internet connection is available
If available, it directly calls web service to upload data
If not available, it will return to #3
Back to my last development on < iOS 7, previously background time was 10 minutes but becomes 3 minutes.
Background Fetch:
When this method is called, your app has up to 30 seconds of
wall-clock time to perform the download operation and call the
specified completion handler block. In practice, your app should call
the completion handler block as soon as possible after downloading the
needed data. If you do not call the completion handler in time, your
app is terminated.
Also that these are the only apps allowed to do background:
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 (Background Fetch)
Apps that receive regular updates from external accessories
Isn't there any way I can do background in iOS yet or at least I can get the network status in background?
Note: My app is for internal distribution only, no need to worry with rejection.

Answer 1

What you need to do is using NSURLSession instead of NSURLConnection (in case you are still using it)
Difference between NSURLSession and NSURLConnection
NSURLConnection: if we have an open connection with NSURLConnection and the system interrupt our App, when our App goes to background mode, everything we have received or sent were lost.
NSURLSession: solve this problem and also give us out of process downloads. It manage the connection process even when we don't have access. You will need to use application:handleEventsForBackgroundURLSession:completionHandler in your AppDelegate
So with the use of NSURLSession, you don't need to manage or to check
your internet connection because OS does it for you.
Extra: How to check internet connection in my iOS app
Disclaimer: I'm not sure that the following Framework can run in background mode
You can use framework Rechability to check if your device have internet connection.
https://github.com/tonymillion/Reachability
It is a drop-in replacement for Apple's Reachability class and it supports blocks to perform action when you receive the NSNotification of reachability changed.
You can check the README.md at his repo but it is very simple to use.
Using NSNotification
1
In your AppDelegate you have to call
[Reachability reachabilityWithHostname:#"www.google.com"];
Also, you will need to declare a property to store that value
#property (strong, nonatomic) Reachability *reach;
so now you will have to put the following code inside your application:didFinishLaunchingWithOptions:
_reach = [Reachability reachabilityWithHostname:#"www.google.com"];
2
In the Controller you need to check if reachability state, you must subscribe to that notification
[[NSNotificationCenter defaultCenter] addObserver:_sharedInstance selector:#selector(reachabilityDidChange:) name:#"kReachabilityChanged" object:nil];
3
Now you can implement the selector reachabilityDidChange: where you check if now are connected or not. Put it in the same Controller.
- (void)reachabilityDidChange:(NSNotification *)note
{
Reachability * reach = (Reachability *)[note object];
if (self.appDelegate.wasConnected != [reach isReachable]){
if ([reach isReachable]){
NSLog(#"Notification Says Reachable");
[[NSNotificationCenter defaultCenter] postNotificationName:#"ConnectionIsReachable" object:nil];
[self sendPendingOperations];
}else{
[[NSNotificationCenter defaultCenter] postNotificationName:#"ConnectionIsUnreachable" object:nil];
NSLog(#"Notification Says Unreachable");
}
self.appDelegate.wasConnected = [reach isReachable];
}
}
As you can see, we store the last connection state also in a AppDelegate property
`#property BOOL wasConnected;`
4
Now you have to subscribe to those new notifications (ConnectionIsReachable, ConnectionIsUnreachable) and perform the action you need to do.
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(showNoConnectionAlert) name:#"ConnectionIsUnreachable" object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(hideNoConnectionAlert) name:#"ConnectionIsReachable" object:nil];
Using blocks
I have not test it that feature but I copy to you the official documentation
// Allocate a reachability object
Reachability* reach = [Reachability reachabilityWithHostname:#"www.google.com"];
// Set the blocks
reach.reachableBlock = ^(Reachability*reach)
{
// keep in mind this is called on a background thread
// and if you are updating the UI it needs to happen
// on the main thread, like this:
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(#"REACHABLE!");
});
};
reach.unreachableBlock = ^(Reachability*reach)
{
NSLog(#"UNREACHABLE!");
};
// Start the notifier, which will cause the reachability object to retain itself!
[reach startNotifier];