iOS 7 provides multitasking API to fetch/download the content regularly in background. Using iOS background fetch API, your App can register with the system and get callback to download the content in background.
Prerequisites:
1). You need add UIBackgroundModes key with the fetch value in your app’s Info.plist file
Info.plist source contains:
<key>UIBackgroundModes</key> <array> <string>fetch</string> </array>
2). You need to implement application:performFetchWithCompletionHandler in app delegate
-(void)application:(UIApplication *)application performFetchWithCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler
{
//Tell the system that you ar done.
completionHandler(UIBackgroundFetchResultNewData);
}
How to initialize:
[[UIApplication sharedApplication] setMinimumBackgroundFetchInterval:minimumBackgroundFetchInterval];
If minimumBackgroundFetchInterval is UIApplicationBackgroundFetchIntervalMinimum, then system will decide when to call performFetchWithCompletionHandler method.
If minimumBackgroundFetchInterval is UIApplicationBackgroundFetchIntervalNever, then system will never call callback handler.
This API is not like a timer task, system will decide when to call the handler depending on many constraints.so if you set timeInterval to 2.00f( 2secs), handler is called for every 2+(minimum 2)secs.
Restrictions:
When performFetchWithCompletionHandler method is called, app has up to 30 seconds of time to perform the download operation and call the specified completion handler block. If the completion handler is not called in time, then your app will be suspended.
Example:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
[[UIApplication sharedApplication] setMinimumBackgroundFetchInterval:UIApplicationBackgroundFetchIntervalMinimum];
return YES;
}
-(void)application:(UIApplication *)application performFetchWithCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler
{
NSLog(@"########### Received Background Fetch ###########");
//Download the Content .
//Cleanup
completionHandler(UIBackgroundFetchResultNewData);
}
Testing Background fetch in Simulator?
You can test background fech in two methods.
1). Run your app in simulator. In XCode Menu, Go to “Debug” => “Simulate Background Fetch”.
after this performFetchWithCompletionHandler() is called.
2). In XCode Menu, Go to “Product” => “Scheme” => “Edit Scheme”
enable the option “Background Fetch“. Rebuild and Run you app. performFetchWithCompletionHandler() is called while launching the app
