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Areas alarms

Estimated reading time: 3 minutes

Another powerful use case is triggering operations the moment a user enters or exits a defined geographic area.

The Magic Lane Flutter SDK includes a built-in AlarmService class, making it effortless to configure and manage all your geofence events.

Add areas to be monitored​

Define your geographic areas—RectangleGeographicArea, CircleGeographicArea, and PolygonGeographicArea—then invoke the monitorArea method on your AlarmService instance:

final RectangleGeographicArea rect = RectangleGeographicArea(
    topLeft: Coordinates(latitude: 1, longitude: 0.5),
    bottomRight: Coordinates(latitude: 0.5, longitude: 1),
);

final CircleGeographicArea circle = CircleGeographicArea(
    centerCoordinates: Coordinates(latitude: 1, longitude: 0.5),
    radius: 100,
);

final PolygonGeographicArea polygon = PolygonGeographicArea(coordinates: [
    Coordinates(latitude: 1, longitude: 0.5),
    Coordinates(latitude: 0.5, longitude: 1),
    Coordinates(latitude: 1, longitude: 1),
    Coordinates(latitude: 1, longitude: 0.5),
]);

alarmService!.monitorArea(rect, id: 'areaRect');
alarmService!.monitorArea(circle, id: 'areaCircle');
alarmService!.monitorArea(polygon, id: 'areaPolygon');

Assign a unique identifier string to each area you monitor—this lets you easily determine which specific zone a user has entered or exited.

Get a list of monitored areas​

Access your active geofences via the monitoredAreas getter, which returns a list of AlarmMonitoredArea objects, each one reflecting the parameters you provided to monitorArea.

List<AlarmMonitoredArea> monitorAreas = alarmService.monitoredAreas;

for (final monitorArea in monitorAreas){
    final GeographicArea area = monitorArea.area;
    final String id = monitorArea.id;
}
tip

When defining a PolygonGeographicArea, always “close” the shape by making the first and last coordinates identical. Otherwise, the SDK may return polygons that don’t match the one you provided.

Unmonitor an area​

To remove a monitored area, call the unmonitorArea method and pass in the same GeographicArea instance you originally supplied to monitorArea. This will unregister that zone and stop all related geofence events.

final RectangleGeographicArea rect = RectangleGeographicArea(
    topLeft: Coordinates(latitude: 1, longitude: 0.5),
    bottomRight: Coordinates(latitude: 0.5, longitude: 1),
);
alarmService!.monitorArea(rect);

alarmService!.unmonitorArea(rect);

The unmonitorAreasByIds method can be also used by passing the list of ids to be unmonitored:

alarmService.unmonitorAreasByIds(['firstIdToUnmonitor', 'secondIdToUnmonitor'])

Get notified when the user enters an area:​

Attach your AlarmListener—including the onBoundaryCrossed callback—to your AlarmService. This callback returns two arrays: one of area IDs the user has entered, and another of those they’ve exited.

AlarmListener(
    onBoundaryCrossed: (List<String> entered, List<String> exited) {
        print("ENTERED AREAS: ${entered}");
        print("EXITED AREAS: ${exited}");
    }
);

alarmService = AlarmService(alarmListener);

Get the list of areas where the user is located​

Retrieve the zones the user is currently inside by calling the insideAreas getter on your AlarmService instance:

List<AlarmMonitoredArea> insideAreas = alarmService.insideAreas;
note

For the insideAreas getter to return a non-empty list, the user must be inside at least one monitored area and must move or change position within that area.

To retrieve the zones the user has exited, call the outsideAreas getter on your AlarmService instance.