Question

我有一个应用程序，可以在核心数据managedObjectContext中存储兴趣点（POI）。我的目标是，如果currentLocation在managedObjectContext的POI的指定范围内，则会发出警报。在阅读CLRegion时，似乎可以监控的区域数量上限为20。

为了解决区域监控上限问题，我的游戏计划是浏览我的managedObjectContext的纬度/经度坐标，并在每次我的位置管理员didUpdateLocations在我的应用中触发时计算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。在这种情况下，我没有显示任何内容 - 相反，当MOC触发时，我正在浏览didUpdateLocations中的对象，拉出坐标并计算距离。任何想法如何实现这一目标？

Answer 1

我打电话给我的班级LocationManager，这是一个单身人士班。在标题中，我为NSManagedObjectContext添加了一个属性。

.h

@property (nonatomic, weak) NSManagedObjectContext *managedObjectContext;

我的核心数据堆栈在我的AppDelegate中，因此我调整了LocationManager实现的init方法以“看到”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;
}

再往下，当didUpdateLocations方法触发时，我添加了对[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);
    }
}

位置警报使用Core Data来绕过CLRegion 20区域上限

1 个答案: