Background fetch not updating UI - objective-c

Question

I'm new to ios7 background fetch. Here is how I'm doing it.
This is what is going on in appDelegate:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
NSURL *url = [[NSURL alloc] initWithString:#"http://sample.com/api/home/lastnews"];
OldJson = [NSString stringWithContentsOfURL:url encoding:NSUTF8StringEncoding error:nil];
}
Note that here I'm storing the whole JSON file in a string so i can use to check for new content.
- (void)application:(UIApplication *)application performFetchWithCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler
{
//HomepageView is the view controller that is supposed to be updated
HomepageView *homepage = [[HomepageView alloc] init];
NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfiguration];
NSURL *url = [[NSURL alloc] initWithString:#"http://sample.com/api/home/lastnews"];
NewJson = [NSString stringWithContentsOfURL:url encoding:NSUTF8StringEncoding error:nil];
NSURLSessionDataTask *task = [session dataTaskWithURL:url
completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
if (error) {
completionHandler(UIBackgroundFetchResultFailed);
return;
}
if (![NewJson isEqualToString:OldJson])
{
completionHandler(UIBackgroundFetchResultNewData);
NSLog(#"New Data : %#",NewJson);
}
else
{
completionHandler(UIBackgroundFetchResultNoData);
NSLog(#"Old Json : %#",OldJson);
}
}];
// Start the task
[task resume];
}
Now to test the whole process, i simply run the application. Then i send it to background and then when i have new content in the JSON file, i use the Simulate Background Fetch operation from the Debug menu. Then i open the application but nothing has changed.

Answer 1

First store your newJson in NSUserDefaults as seen below
if (![NewJson isEqualToString:OldJson])
{
completionHandler(UIBackgroundFetchResultNewData);
NSLog(#"New Data : %#",NewJson);
NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
[defaults setObject:NewJson forKey:#"newJson"];
}
Second in your View Controller add this in the ViewDidLoad
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(refresh:) name: UIApplicationWillEnterForegroundNotification object:nil];
Add this to your viewWillAppear
-(void)viewWillAppear:(BOOL)animated{
[self loadData];
}
Create the loadData
- (void)loadData {
// contains information the ViewController makes use of
NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
textView.text = [defaults objectForKey:#"newJson"];
}
Finally add your action
-(IBAction)refresh:(id) sender {
NSLog(#"I ran");
[self loadData];
}
I tested this and it works.

Answer 2

Three problems:
There's no guarantee that JSON data comes in UTF-8 format. Use [NSData dataWithContensOfURL:...]
Never, ever access a URL from the main thread. If the server doesn't respond, your app will be hanging.
Really bad: In your background fetch handler, you actually load the URL synchronously. And then you create a task to load it again. So you load it actually twice.