能否通过Android Fused Location Provider Client获取NMEA语句？

Great question! The short answer is: No, you can't directly get raw NMEA sentences via the Fused Location Provider (FLP) Client.

Let me break down why, and what you can do instead:

Why FLP Doesn't Support NMEA #

The Fused Location Provider is built as a high-level, simplified API. It takes data from multiple sources (GPS, Wi-Fi, cell towers, sensors), processes it to deliver optimized, reliable location updates, and intentionally hides low-level details like raw NMEA strings. Its core goal is to make location access easy for developers, not to expose raw GNSS hardware data.

The Alternative: Use LocationManager #

If you need raw NMEA sentences, you’ll have to use the lower-level LocationManager API, which gives direct access to GNSS receiver data. Here’s a step-by-step guide to implement this:

1. Add Required Permissions to Manifest #

First, update your AndroidManifest.xml with permissions and a GNSS feature declaration:

<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<!-- For Android 12+, add this if you need background NMEA access -->
<uses-permission android:name="android.permission.ACCESS_BACKGROUND_LOCATION" />
<uses-feature android:name="android.hardware.location.gnss" android:required="true" />

2. Implement the NMEA Listener #

Here’s a Kotlin example (Java follows similar logic) of setting up the listener in an Activity:

import android.location.LocationManager
import android.os.Bundle
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import android.Manifest
import android.content.pm.PackageManager

class NmeaReaderActivity : AppCompatActivity() {
    private lateinit var locationManager: LocationManager

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_nmea_reader)

        locationManager = getSystemService(LOCATION_SERVICE) as LocationManager

        // Check if GPS is enabled on the device
        if (!locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER)) {
            Toast.makeText(this, "Enable GPS to receive NMEA data", Toast.LENGTH_SHORT).show()
            return
        }

        // Handle runtime location permissions (required for Android 6.0+)
        if (checkSelfPermission(Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            requestPermissions(arrayOf(Manifest.permission.ACCESS_FINE_LOCATION), 100)
            return
        }

        // Start listening for NMEA sentences
        setupNmeaListener()
    }

    private fun setupNmeaListener() {
        locationManager.addNmeaListener { nmeaSentence, timestamp ->
            // This callback receives raw NMEA strings
            println("Raw NMEA Sentence: $nmeaSentence")
            
            // Example: Filter and process specific sentence types
            when {
                nmeaSentence.startsWith("\$GPGGA") -> {
                    // Handle GGA (fix quality and location data)
                }
                nmeaSentence.startsWith("\$GPRMC") -> {
                    // Handle RMC (recommended minimum navigation data)
                }
            }
        }
    }

    override fun onRequestPermissionsResult(
        requestCode: Int,
        permissions: Array<out String>,
        grantResults: IntArray
    ) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults)
        if (requestCode == 100 && grantResults.isNotEmpty() && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
            setupNmeaListener()
        } else {
            Toast.makeText(this, "Location permission is required to access NMEA data", Toast.LENGTH_SHORT).show()
        }
    }
}

Key Notes #

• Runtime Permissions: Always check and request ACCESS_FINE_LOCATION at runtime. For background NMEA access on Android 10+, you’ll also need ACCESS_BACKGROUND_LOCATION (and comply with Google Play policy requirements).
• GNSS Availability: The listener only receives data if the device has a working GNSS receiver and GPS is enabled in system settings.
• Battery Impact: Raw GNSS access uses more battery than FLP’s optimized updates, so consider this for your app’s use case.

内容的提问来源于stack exchange，提问作者Daitarn