使用核心数据获取CLRegion 20区域上限的位置警报

Question

我有一个在核心数据managedObjectContext中存储感兴趣点(POI)的应用程序。我的目标是，如果currentLocation在managedObjectContext中POI的指定范围内，就会发出警报。在阅读有关CLRegion的文章时，可以监视的区域的数量似乎限制在20个。

为了绕过区域监控帽，我的游戏计划是在每次我的位置管理器的managedObjectContext在我的应用程序中触发时，浏览我的didUpdateLocations中的纬度/经度坐标，并计算POI之间的距离：

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations {
    CLLocation *location = [locations lastObject];
    NSLog(@"LocationManager Latitude %+.6f, Longitude %+.6f\n",
          location.coordinate.latitude,
          location.coordinate.longitude);
    // TODO: compute distances between objects in managedObjectContext
    [self calculateDistances];
    self.currentLocation = location;
}

// method to compute distances
- (void) calculateDistances {

    // for POI in managedObjectContext, do the following
    CLLocation *locA = [[CLLocation alloc] initWithLatitude:self.currentLocation.coordinate.latitude longitude:self.currentLocation.coordinate.longitude];

    CLLocation *locB = [[CLLocation alloc] initWithLatitude:POIlatitude longitude:POIlongitude];

    CLLocationDistance distance = [locA distanceFromLocation:locB];

    if (distance < 1000) {
        // popup alert
    }

}

我只使用managedObjectContext来显示数据。在本例中，我没有显示任何内容--而是在运行我的MOC中的对象时，didUpdateLocations触发、提取坐标和计算距离。有什么办法做到这一点吗？

Answer 1

我调用了我的类LocationManager，这是一个单例类。在标头中，我为NSManagedObjectContext添加了一个属性。

.h

@property (nonatomic, weak) NSManagedObjectContext *managedObjectContext;

我的核心数据堆栈位于我的AppDelegate中，因此我调整了LocationManager实现的init方法，以“查看”它：

.m

- (id)init {
    self = [super init];
    if (!self.locationManager) {
        // This is so I can get a reference to the managedObjectContext
        AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
        self.managedObjectContext = appDelegate.managedObjectContext;

        self.locationManager = [[CLLocationManager alloc]init];

        if ([self.locationManager respondsToSelector:@selector(requestAlwaysAuthorization)]) {
            [self.locationManager requestAlwaysAuthorization];
        }

        self.locationManager.desiredAccuracy = kCLLocationAccuracyHundredMeters;
        self.locationManager.distanceFilter = 100; // meters
        self.locationManager.delegate = self;
    }
    return self;
}

接下来，当didUpdateLocations方法触发时，我添加了一个对[self calculateDistances]的调用，如下所示：

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations {
    CLLocation *location = [locations lastObject];
    NSLog(@"LocationManager Latitude %+.6f, Longitude %+.6f\n",
          location.coordinate.latitude,
          location.coordinate.longitude);
    [self calculateDistances];
    self.currentLocation = location;
}

// method to compute distances
- (void) calculateDistances {

    NSError *error;
    NSFetchRequest *coordinateRetrieval = [[NSFetchRequest alloc]initWithEntityName:@"PointOfInterest"];
    NSArray *pois = [self.managedObjectContext executeFetchRequest:coordinateRetrieval error:&error];

    for (PointOfInterest *venue in poi) {
        CLLocation *locA = self.currentLocation;
        CLLocation *locB = [[CLLocation alloc]initWithLatitude:[venue.latitude doubleValue] longitude:[venue.longitude doubleValue]];
        CLLocationDistance distance = [locA distanceFromLocation:locB];

        if (distance < 1000) {
            // popup alert
        }
        NSLog(@"The distance from currentLocation to venue is %lf meters", distance);
    }
}