CLLocationManager位置监视无法正常工作

Question

I have an app that will notify the user every time he approaches to one of my client's stores. There are more than 20 stores, so I have a function that takes the user's location and finds the 20 nearest stores to him and start monitoring the location of these stores, every time the user moves, the app finds the 20 nearest stores again, removes the previous stores from monitoring and start monitoring the new ones.

For some reason, it doesn't work, I'll be happy if one of you (or more :)) will help me to find the problem, Thanks!!

myCode (scroll to see the full code):

Note: the CLLocationManager created on the AppDelegate.m and it's delegate is this class ( UIViewController ).

-(void)sortClosestStores
{
    [self.allStores sortUsingComparator:^NSComparisonResult(id  _Nonnull obj1, id  _Nonnull obj2) {
        CLLocation *location1=[[CLLocation alloc] initWithLatitude:((Store*)obj1).geoPoint.latitude longitude:((Store*)obj1).geoPoint.longitude];
        CLLocation *location2=[[CLLocation alloc] initWithLatitude:((Store*)obj2).geoPoint.latitude longitude:((Store*)obj2).geoPoint.longitude];

    float dist1 =[location1 distanceFromLocation:self.locationManager.location];
    float dist2 = [location2 distanceFromLocation:self.locationManager.location];
    if (dist1 == dist2) {
        return NSOrderedSame;
    }
    else if (dist1 < dist2) {
        return NSOrderedAscending;
    }
    else {
        return NSOrderedDescending;
    }
}];

if (self.twentyClosestStores==nil) {
    self.twentyClosestStores=[NSMutableArray array];
}

if (self.previousTwentyStores==nil) {
    self.previousTwentyStores=[NSMutableArray array];
}
self.previousTwentyStores=self.twentyClosestStores;
self.twentyClosestStores=[NSMutableArray array];

for (int i = 0; i < 20; i++) {
    [self.twentyClosestStores addObject:[self.allStores objectAtIndex:i]];
    }
}

-(void)startMonitoringClosestStores
{
    if (![CLLocationManager isMonitoringAvailableForClass:[CLCircularRegion class]]) {
        NSLog(@"Monitoring is not available for CLCircularRegion class");
    }

    for (Store *currentStore in self.twentyClosestStores) {
        CLCircularRegion *region=[currentStore createCircularRegion];
         [self.locationManager startMonitoringForRegion:region];
    }
}
-(void)stopMonitoringStores
{
    for (Store *currentStore in self.previousTwentyStores) {
        CLCircularRegion *region=[currentStore createCircularRegion];
        [self.locationManager stopMonitoringForRegion:region];
    }
}

-(void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray<CLLocation *> *)locations
{
    if (self.allStores!=nil) {
        [self sortClosestStores];
        [self stopMonitoringStores];
        [self startMonitoringClosestStores];
    }
}


-(void)locationManager:(CLLocationManager *)manager didEnterRegion:(CLRegion *)region
{
    NSLog(@"Entered"); //Not called even when the user enters one of the regions.
}

Can you please help me? Thanks!

Answer 1

I'm pretty new at CoreLocation myself but I would think that it is not a good idea to call stopMonitoringForRegions and startMonitoringForRegions in didUpdateLocations.

Since you're monitoring regions, the didEnterRegion delegate is what you will be interested in. That will give you the 'hey, I arrived at the X store' event, and in there is where you would probably want to call the code that you currently have in your didUpdateLocations.

You will want to setup CoreLocation probably in your AppDelegate, so you might have something like (sorry about it being Swift, that's what I'm working in right now):

locationManager.delegate = self
// auths:
locationManager.requestAlwaysAuthorization()
locationManager.requestWhenInUseAuthorization()
// config:
locationManager.distanceFilter = kCLDistanceFilterNone
locationManager.desiredAccuracy = kCLLocationAccuracyBest
locationManager.pausesLocationUpdatesAutomatically = true
locationManager.allowsBackgroundLocationUpdates = true
locationManager.activityType = CLActivityType.AutomotiveNavigation

// start:
locationManager.startMonitoringSignificantLocationChanges()

Then you would have your code:

if (self.allStores!=nil) {
    [self sortClosestStores];
    [self stopMonitoringStores];
    [self startMonitoringClosestStores];
}

Note: I don't think it matters if you call startMonitoringSignificantLocationChanges before or after adding monitored regions, I haven't gotten quite that far in my code yet.

didUpdateLocations is more for when you want to track location eg tracking a bicycle ride or jogging session.

Additional explanation: OK, I think I understand the issue now. There are two aspects to what you want to accomplish:

• being notified when the user enters a store's region
• dynamically recalculating the nearest N stores as the device moves

My previous answer was geared towards the first issue. Regarding the second issue, dynamically recalulating nearest N, the code in your didUpdateLocations will not be called unless you tell the location manager to startUpdatingLocation. Just off the top of my head:

// configure the location manager in AppDelegate:
// You will need to experiment with these two properties,
// you probably don't want to use kCLLocationAccuracyBestForNavigation. 
// Maybe kCLLocationAccuracyKilometer would be sufficient.
locmgr.distanceFilter = n
locmgr.desiredAccuracy = m
locmgr.pausesLocationUpdatesAutomatically = true
locmgr.startUpdatingLocation()



// this is the delegate that will receive the events due to locmgr.startUpdatingLocation
locationManager:didUpdateLocation {
    // Unless you have a specific need for it, I would refactor so that
    // you don't need self.PreviousTwentyStores:
    [self stopMonitoringStores];
    [self sortClosestStores];
    [self startMonitoringClosestStores];
}


locationManager:didEnterRegion {
    // you are in the region surrounding one of the stores.
}

Alternately, consider just setting a timer and waking the app every N seconds or minutes to recalculate the nearest stores.

As I understand the various aspects of CoreLocation

startUpdatingLocation -> didUpdateLocations -> stopUpdatingLocation

is (in one sense) entirely separate from:

startMonitoringForRegion -> didEnterRegion | didExitRegion -> stopMonitoringForRegion

Additionally, startUpdatingLocation was never called so your didUpdateLocation was never called.