iOS background Location not sending http request

问题:

My app needs to track the users location in the background but it is failing to send a 'get' request. The http request gets sent immediately when the app comes to the foreground. I am using RestKit for all my network requests and I followed this tutorial to setup my background locations service. In my applicationDidEnterBackground

-(void)applicationDidEnterBackground:(UIApplication *)application
{
    self.bgLocationManager = [[CLLocationManager alloc] init];
    self.bgLocationManager.delegate = self;
    [self.bgLocationManager startMonitoringSignificantLocationChanges];
    NSLog(@"Entered Background");
}

and I stopMonitoringSignificantLocationChange in my applicationDidBecomeActive delegate

This is my locationManager delegate where I accept the new updated location and send to my server

-(void) locationManager:(CLLocationManager *)manager 
    didUpdateToLocation:(CLLocation *)newLocation 
           fromLocation:(CLLocation *)oldLocation
{
    NSLog(@"I am in the background");
    bgTask = [[UIApplication sharedApplication]
                beginBackgroundTaskWithExpirationHandler:
                ^{
                      [[UIApplication sharedApplication] endBackgroundTask:bgTask];
                 }];
                 // ANY CODE WE PUT HERE IS OUR BACKGROUND TASK

    NSString *currentLatitude = [[NSString alloc]
                                  initWithFormat:@"%g",
                                  newLocation.coordinate.latitude];
    NSString *currentLongitude = [[NSString alloc]
                                   initWithFormat:@"%g",
                                   newLocation.coordinate.longitude];
    NSString *webToken = [[NSUserDefaults standardUserDefaults] stringForKey:@"userWebToken"];
    NSLog(@"I am in the bgTask, my lat %@", currentLatitude);

    NSDictionary *queryParams;
    queryParams = [NSDictionary dictionaryWithObjectsAndKeys:webToken, @"auth_token",  currentLongitude, @"lng", currentLatitude, @"lat", nil];
    RKRequest* request = [[RKClient sharedClient] post:@"/api/locations/background_update" params:queryParams delegate:self];
    //default is RKRequestBackgroundPolicyNone
    request.backgroundPolicy = RKRequestBackgroundPolicyContinue;

    // AFTER ALL THE UPDATES, close the task

    if (bgTask != UIBackgroundTaskInvalid)
    {
        [[UIApplication sharedApplication] endBackgroundTask:bgTask];
        bgTask = UIBackgroundTaskInvalid;
    }
}

The network requests works as planned but it will not get called in the background. Is there any additional steps I need? In my info.plist I have the Required Background modes key and location-services as the value.

EDIT

I also referred to this past SO answer. I ran some tests with putting logs throughout the didUpdateToLocation call and they were all called but the 'get' request was not sent. Instead when I finally launch the app to the foreground it sent all the built of network requests (over 10).

EDIT (2) I added RKRequestBackgroundPolicyContinue to my request but it did not change my results. (As you can see here in the background upload/download for restkit). I see Restkit initialize the host but fails to send the request until the app becomes active.

ANSWER

RestKit must be doing something that is prohibited in the background. Using an NSURLRequest works perfectly.

NSMutableURLRequest * urlRequest = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"http://www.example.com/api/locations/background_update"]];
[urlRequest setValue:@"application/json" forHTTPHeaderField:@"Accept"];
[urlRequest setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];
[urlRequest setHTTPMethod:@"POST"];
[urlRequest setHTTPBody:jsonData];

NSHTTPURLResponse  *response = nil;
[NSURLConnection sendSynchronousRequest:urlRequest
                      returningResponse:&response
                                  error:&error];

It is fine to use a synchronous request since there is no UI to disrupt with background tasks

回答1:

Re-creating original suggestion as an answer

Have your try replacing your restKit calls with a stock synchronous NSURLConnection? – dklt Sep 20

回答2:

I'm using exactly the same code as you and it works for me in RestKit. The only way I could make it work is ny creating a synchronous request (it doesn't make a lot of sense to do it asynchronously in this context anyway!). Please check this code and let us know if it works:

// REMEMBER. We are running in the background if this is being executed.
// We can't assume normal network access.
// bgTask is defined as an instance variable of type UIBackgroundTaskIdentifier

// Note that the expiration handler block simply ends the task. It is important that we always
// end tasks that we have started.

_bgTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:
           ^{
               [[UIApplication sharedApplication] endBackgroundTask:_bgTask];
           }];

// ANY CODE WE PUT HERE IS OUR BACKGROUND TASK

// For example, I can do a series of SYNCHRONOUS network methods (we're in the background, there is
// no UI to block so synchronous is the correct approach here).

NSNumber *latNumber = [NSNumber numberWithDouble:location.coordinate.latitude];
NSNumber *lngNumber = [NSNumber numberWithDouble:location.coordinate.longitude];
NSNumber *accuracyNumber = [NSNumber numberWithDouble:location.horizontalAccuracy];
NSDictionary *params = [NSDictionary dictionaryWithKeysAndObjects:@"lat",latNumber,@"lng",lngNumber,@"accuracy",accuracyNumber, nil];
RKURL *URL = [RKURL URLWithBaseURL:[NSURL URLWithString:SERVER_URL] resourcePath:@"/user/location/update" queryParameters:params];
RKRequest *request = [RKRequest requestWithURL:URL];
request.method = RKRequestMethodGET;
NSLog(@"Sending location to the server");
RKResponse *response = [request sendSynchronously];
if (response.isFailure)
    NSLog(@"Unable to send background location, failure: %@", response.failureErrorDescription);
else {
    NSError *error = nil;
    NSDictionary *parsedBody = [response parsedBody:&error];
    if (YES == [[parsedBody objectForKey:@"result"] boolValue]){
        NSLog(@"Background location sent to server");
    }
    else {
        //Something went bad
        NSLog(@"Failed to send background location");
    }
}
// AFTER ALL THE UPDATES, close the task

if (_bgTask != UIBackgroundTaskInvalid)
{
    [[UIApplication sharedApplication] endBackgroundTask:_bgTask];
    _bgTask = UIBackgroundTaskInvalid;
}

I'm almost sure the new thread spawned for your RKClient request is automatically killed after invoking it.

回答3:

When you're application is running in the background you can finish a HTTP request you started before you entered the background but you cannot initiate a new request. You can only initiate certain network operations while in the background (voip, newsstand).