I want to calculate directions to a destination when my app is in the background every time it receives a location update.
However, the [MKDirections calculateDirectionsWithCompletionHandler] is an asynchronous call, and my question is therefore: will my app be terminated if this takes more than 5 seconds to complete after my app has received a location update? What would be your recommendations to make sure this request has enough time to finish?
In order to request extra time for your app to run in the background to complete its tasks (asynchronous or not), you can use beginBackgroundTaskWithExpirationHandler:.
For example:
- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation {
// If the application is in the background...
if([[UIApplication sharedApplication] applicationState] != UIApplicationStateActive) {
// Create the beginBackgroundTaskWithExpirationHandler
// which will execute once your task is complete
bgTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
// Clean up any unfinished task business by marking where you
// stopped or ending the task outright.
[application endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}];
// Start the long-running task and return immediately.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
[dict setObject:application forKey:#"application"];
// Start a timer to keep the program alive for 180 seconds max
// (less if that's all that's necessary)
[NSTimer scheduledTimerWithTimeInterval:180 target:self selector:#selector(delayMethod:) userInfo:nil repeats:NO];
});
}
// ... the rest of your didUpdateToLocation: code ...
}
- (void)delayMethod:(NSTimer*)timer {
// End the background task you created with beginBackgroundTaskWithExpirationHandler
[[[timer userInfo] objectForKey:#"application"] endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}
Related
I have some NSOperations that are started regularly in my application. They should complete even when the the application is put to background. For this, I'm using the beginBackgroundTaskWithExpirationHandler method.
Am I supposed to use the beginBackgroundTaskWithExpirationHandler/ endBackgroundTask: every time I start my task even if the app is not going to background? Or am I supposed the call the begin/end methods only when I detected a UIApplicationDidEnterBackgroundNotification?
Option 1: Use background task every time
/**
* This method is called regularly from a NSTimer
*/
- (void)processData
{
__block UIBackgroundTaskIdentifier operationBackgroundId = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
[[UIApplication sharedApplication] endBackgroundTask:operationBackgroundId];
operationBackgroundId = UIBackgroundTaskInvalid;
}];
NSOperation *operation = ...
[self.queue addOperation:operation];
operation.completionBlock = ^{
[[UIApplication sharedApplication] endBackgroundTask:operationBackgroundId];
operationBackgroundId = UIBackgroundTaskInvalid;
};
}
Option 2: Use background task only when the application is about to go to background
/**
* This method is called regularly from a NSTimer
*/
- (void)processData
{
NSOperation *operation = ...
[self.queue addOperation:operation];
}
- (void)applicationDidEnterBackground:(NSNotification *)notification
{
__block UIBackgroundTaskIdentifier operationBackgroundId = [[UIApplication sharedApplication] beginBackgroundTaskWithName:#"EnterBackgroundFlushTask" expirationHandler:^{
[[UIApplication sharedApplication] endBackgroundTask:operationBackgroundId];
operationBackgroundId = UIBackgroundTaskInvalid;
}];
// wait for all operations to complete and then
// let UIApplication know that we are done
[[UIApplication sharedApplication] endBackgroundTask:operationBackgroundId];
}
Answering my own question. From the Apple Docs:
You do not need to wait until your app moves to the background to
designate background tasks. A more useful design is to call the
beginBackgroundTaskWithName:expirationHandler: or
beginBackgroundTaskWithExpirationHandler: method before starting a
task and call the endBackgroundTask: method as soon as you finish. You
can even follow this pattern while your app is executing in the
foreground.
Other Apple API reference:
You should call this method at times where leaving a task unfinished might be detrimental to your app’s user experience.
You can call this method at any point in your app’s execution.
Option2 is correct option.Here is code from Apple document for your reference.
- (void)applicationDidEnterBackground:(UIApplication *)application
{
bgTask = [application beginBackgroundTaskWithName:#"MyTask" expirationHandler:^{
// Clean up any unfinished task business by marking where you
// stopped or ending the task outright.
[application endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}];
// Start the long-running task and return immediately.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// Do the work associated with the task, preferably in chunks.
[self processData];
[application endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
});
}
Apple developer Guide
I have a app that fetch some content from server via REST api after every 5 mins in background using the UIBackgroundTaskIdentifier. My problem is that this works fine for 1,2 hours and then after it is expired it never re starts the background task. The code I am using is given below,
In AppDelegate.m
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
UIApplication* app = [UIApplication sharedApplication];
self.expirationHandler = ^{
[app endBackgroundTask:self.bgTask];
self.bgTask = UIBackgroundTaskInvalid;
// self.bgTask = [app beginBackgroundTaskWithExpirationHandler:expirationHandler];
NSLog(#"Expired");
self.jobExpired = YES;
while(self.jobExpired) {
// spin while we wait for the task to actually end.
[NSThread sleepForTimeInterval:1];
}
self.bgTask = [app beginBackgroundTaskWithExpirationHandler:expirationHandler];
// Restart the background task so we can run forever.
[self startBackgroundTask];
};
self.bgTask = [app beginBackgroundTaskWithExpirationHandler:expirationHandler];
[self monitorBatteryStateInBackground];
}
- (void)monitorBatteryStateInBackground
{
NSLog(#"Monitoring update");
self.background = YES;
[self startBackgroundTask];
}
- (void)startBackgroundTask
{
NSLog(#"Restarting task");
// Start the long-running task.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// When the job expires it still keeps running since we never exited it. Thus have the expiration handler
// set a flag that the job expired and use that to exit the while loop and end the task.
while(self.background && !self.jobExpired)
{
[self uploadPhotostoServer];
[NSThread sleepForTimeInterval:240.0];
}
self.jobExpired = NO;
});
}
In expired section it do come but never calls the method [self startBackgroundTask]
Any help will be much appreciated.
How to remain getting the location continuously in the background in iOS8 and you must try your best to save electricity? Can anybody give me some advice?
In your project setting, Select Target and go to Capabilities, turn ON the background mode and tick the location updates and background fetch.
This will add background mode in your project plist.
Now, to get continuous location updates even in background, add this code in AppDelegate's applicationDidEnterBackground: method. This code will kill the background task every time and restart it. So, even when app is in background, you'll receive background location updates.
- (void)applicationDidEnterBackground:(UIApplication *)application {
if ([[UIDevice currentDevice] respondsToSelector:#selector(isMultitaskingSupported)]) { //Check if our iOS version supports multitasking I.E iOS 4
if ([[UIDevice currentDevice] isMultitaskingSupported]) { //Check if device supports mulitasking
UIApplication *application = [UIApplication sharedApplication]; //Get the shared application instance
__block UIBackgroundTaskIdentifier background_task; //Create a task object
background_task = [application beginBackgroundTaskWithExpirationHandler: ^{
[application endBackgroundTask:background_task]; //Tell the system that we are done with the tasks
background_task = UIBackgroundTaskInvalid; //Set the task to be invalid
//System will be shutting down the app at any point in time now
}];
}
}
}
Now to extend device battery life, you can use locationManager:didUpdateLocations: method as it is only called when location changes according to desired accuracy.
- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{
CLLocation *location = [locations lastObject];
if (location != nil) {
strLatitude = [NSString stringWithFormat:#"%f", location.coordinate.latitude];
strLongitude = [NSString stringWithFormat:#"%f", location.coordinate.longitude];
}
}
Found some Solution here
Study the example from Ray Wenderlich. The sample code works perfectly.
You can add timer to it by using this code snippet this may reduce battery consumption a bit :
-(void)applicationDidEnterBackground {
[self.locationManager stopUpdatingLocation];
UIApplication* app = [UIApplication sharedApplication];
bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
[app endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}];
self.timer = [NSTimer scheduledTimerWithTimeInterval:intervalBackgroundUpdate
target:self.locationManager
selector:#selector(startUpdatingLocation)
userInfo:nil
repeats:YES];
}
In my app , I am triggering many GET/POST request and handling the response. But just after initiating the request if I lock the device then on resuming the app after some seconds the response doesn`t come.Is there any way to let the request active even in the background or on the device locked state till the response comes. I went through the Background Execution Docs in iOS but that seems to be used if want to download or do something in background.Not fulfilling my scenario.
If you register a background task for each request, your app will keep running even when the device is locked, as long as a request is still active. The system only allows a maximum of 4 minutes though, so your requests mustn't take too long.
When you start a GET/POST request, do this:
__block UIBackgroundTaskIdentifier bgTask = 0;
bgTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
[[UIApplication sharedApplication] endBackgroundTask:bgTask];
}];
Then, store bgTask somewhere associated with your GET/POST request. Then when your request is complete, do this:
[[UIApplication sharedApplication] endBackgroundTask:bgTask];
Wen app is closed applicationDidEnterBackground was called so put this background task code. put timer or cal the function what ever u want.
- (void)applicationDidEnterBackground:(UIApplication *)application
{
bgTask = [application beginBackgroundTaskWithName:#"MyTask" expirationHandler:^{
[application endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,
0),
^{
[application endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
});
//// just u call the method want ever u want example
[self notification];
// (or) timer
timer = [NSTimer scheduledTimerWithTimeInterval:1.0
target:self
selector:#selector(notification:)
userInfo:nil
repeats:YES];
}
i think is help ful to u
I am a new bee in iOS apps development. I want to create a background service in iOS. I also want to mention a particular time of the day and interval (every 2 hours) to call the service (kind of an Alarm to invoke service). When the service runs, some task should get performed independent of the state of app i.e. app can be in active or inactive state. Any example of it or a code snippet of implementation will help me implement this functionality.
Use this Code
- (void)applicationWillEnterForeground:(UIApplication *)application
{
[Timer invalidate];
Timer = nil;
}
- (void)applicationDidEnterBackground:(UIApplication *)application
{
NSLog(#"Background process is Start(EnterBackground)!");
__block UIBackgroundTaskIdentifier bgTask ;
UIApplication *app = [UIApplication sharedApplication];
bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
[app endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}];
Timer = [NSTimer scheduledTimerWithTimeInterval:120.0f target:self selector:#selector(process) userInfo:nil repeats:YES];
}