Swift区域监控：自定义形状的进入事件触发方案问询

Great question! The built-in CLCircularRegion works perfectly for simple circular geofences, but when dealing with custom polygonal shapes (your CLLocationCoordinate2D array), you'll need to implement a point-in-polygon check or leverage existing SDK functionality. Here's how to solve this:

Option 1: Implement a Point-in-Polygon Algorithm (Core Location Only) #

If you want to avoid relying on Google Maps SDK for the geofence logic, you can use the ray casting algorithm to check if the user's current location falls inside your custom polygon. This works by counting how many times a horizontal ray from the user's point crosses the polygon edges—an odd count means the point is inside.

Here's a Swift implementation you can drop into your code:

func isCoordinate(_ coordinate: CLLocationCoordinate2D, insidePolygon polygon: [CLLocationCoordinate2D]) -> Bool {
    var intersectionCount = 0
    let polygonVertexCount = polygon.count
    
    for i in 0..<polygonVertexCount {
        let currentVertex = polygon[i]
        let nextVertex = polygon[(i + 1) % polygonVertexCount]
        
        // Check if the user's latitude is within the vertical range of the edge
        let isLatitudeInRange = (currentVertex.latitude > coordinate.latitude) != (nextVertex.latitude > coordinate.latitude)
        guard isLatitudeInRange else { continue }
        
        // Calculate where the horizontal ray from the user's point intersects the edge
        let longitudeIntersection = ((coordinate.latitude - currentVertex.latitude) * (nextVertex.longitude - currentVertex.longitude) / (nextVertex.latitude - currentVertex.latitude)) + currentVertex.longitude
        
        // If the user's longitude is left of the intersection, increment the count
        if coordinate.longitude < longitudeIntersection {
            intersectionCount += 1
        }
    }
    
    // Odd count = point is inside the polygon
    return intersectionCount % 2 == 1
}

To use this:

• Set up CLLocationManager to receive location updates
• On each update, fetch the user's current CLLocationCoordinate2D
• Track the user's previous "inside/outside" state, and trigger your event when the state changes from outside to inside

Option 2: Use Google Maps SDK's Built-in Polygon Check #

Since you're already using Google Maps to draw the shape, you can leverage the GMSPolygon class's built-in containsCoordinate(_:) method—this handles the point-in-polygon logic for you, no need to roll your own.

1. First, keep a reference to your drawn polygon:

// Assume your custom coordinates are stored in `customShapeCoordinates`
let polygonPath = GMSPath(coordinates: customShapeCoordinates, count: customShapeCoordinates.count)
let customPolygon = GMSPolygon(path: polygonPath)
customPolygon.map = yourMapView // Add the polygon to your map

2. Then, in your location update handler, check if the user is inside:

var wasInsidePolygon = false

func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
    guard let userCoordinate = locations.last?.coordinate else { return }
    
    let isInsideNow = customPolygon.containsCoordinate(userCoordinate)
    
    // Trigger enter event if state changed from outside to inside
    if !wasInsidePolygon && isInsideNow {
        print("User entered the custom shape!")
        // Add your event handling logic here (e.g., show alert, send notification)
    }
    
    wasInsidePolygon = isInsideNow
}

Key Considerations #

• Battery Efficiency: Don't set desiredAccuracy to the highest level unless absolutely necessary. kCLLocationAccuracyHundredMeters is usually enough for geofencing to balance precision and battery life.
• Background Monitoring: If you need to detect entry while the app is in the background, enable the "Location updates" background mode in your project settings. Note that iOS may throttle background location updates to save battery—consider using significant location changes if your use case allows.
• Large Polygons: For very large or globe-spanning polygons, planar point-in-polygon checks may have minor inaccuracies due to the Earth's curvature. For these cases, you'd need a spherical polygon check using great-circle calculations, but this is rarely needed for most consumer apps.

内容的提问来源于stack exchange，提问作者Dick Thunder