maui-geolocation（毛伊岛地理定位）

.NET MAUI Geolocation

Critical: Always Pass a CancellationToken

GetLocationAsync can hang indefinitely if GPS is off, the device is indoors, or permissions are in a pending state. Always set a timeout.

// ❌ Hangs forever if no GPS fix is available
var location = await Geolocation.Default.GetLocationAsync(
    new GeolocationRequest(GeolocationAccuracy.High));

// ✅ Times out after 30 seconds
using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(30));
var location = await Geolocation.Default.GetLocationAsync(
    new GeolocationRequest(GeolocationAccuracy.High), cts.Token);

Accuracy vs. Battery Trade-off

Use the lowest accuracy that satisfies your feature. Higher accuracy drains battery significantly faster — especially on Android.

Platform Gotchas

iOS 14 reduced accuracy

Users can grant "approximate" location (accuracy > 1 km). Your app receives a location, but it may be useless for precision features.

• Check location.Accuracy — values > 100 m likely indicate reduced precision.
• Use GeolocationRequest.RequestFullAccuracy with a key matching NSLocationTemporaryUsageDescriptionDictionary in Info.plist to prompt for full accuracy.

Android: mock locations in security-sensitive flows

// ⚠️ Always check in security-sensitive flows (e.g., geofence, check-in)
if (location.IsFromMockProvider)
{
    // Reject — user is spoofing location
}

Android: Altitude 0.0 is not sea level

Some Android devices return 0.0 for Altitude when the GPS has no barometric sensor. Treat 0.0 as "unknown", not sea level.

Android 10+: background location requires separate permission

ACCESS_BACKGROUND_LOCATION must be requested separately from foreground permissions and triggers a distinct system dialog. Requesting it together with foreground permissions causes both to be denied on some devices.

GetLastKnownLocationAsync returns null

This is expected on first boot or after a location-data reset. Always fall back to GetLocationAsync:

// ✅ Cache-first with fresh fallback
var location = await geolocation.GetLastKnownLocationAsync();
if (location is null || location.Timestamp < DateTimeOffset.UtcNow.AddMinutes(-5))
{
    location = await geolocation.GetLocationAsync(
        new GeolocationRequest(GeolocationAccuracy.Medium, TimeSpan.FromSeconds(10)), ct);
}

Permissions must be requested before any geolocation call

Call Permissions.RequestAsync<Permissions.LocationWhenInUse>() first, or catch PermissionException. Calling GetLocationAsync without permission throws on some platforms and returns null on others — inconsistent behaviour across platforms.

Continuous Listening: Don't Forget to Unsubscribe

Failing to remove the LocationChanged handler when stopping causes continued GPS usage and battery drain.

// ❌ Forgetting to unsubscribe — GPS stays active
public void StopTracking()
{
    Geolocation.Default.StopListeningForeground();
    // LocationChanged handler still fires!
}

// ✅ Always remove the event handler
public void StopTracking()
{
    Geolocation.Default.StopListeningForeground();
    Geolocation.Default.LocationChanged -= OnLocationChanged;
}

Checklist

• CancellationToken passed to every GetLocationAsync call
• Accuracy level matched to feature need (not blindly set to Best)
• GetLastKnownLocationAsync null-check with GetLocationAsync fallback
• Runtime permissions requested before first geolocation call
• LocationChanged handler removed when stopping continuous listening
• Android: ACCESS_BACKGROUND_LOCATION requested separately (if needed)
• iOS: NSLocationTemporaryUsageDescriptionDictionary added for full-accuracy prompt
• Android: IsFromMockProvider checked in security-sensitive flows