FusedLocationProviderClient 与 Kotlin 协程

Question

我正在尝试使用 FusedLocationProviderClient 和 Kotlin Coroutines 请求新位置。这是我目前的设置：

class LocationProviderImpl(context: Context) : LocationProvider, CoroutineScope {

    private val TAG = this::class.java.simpleName

    private val job = Job()
    override val coroutineContext: CoroutineContext
        get() = job + Dispatchers.IO

    private val fusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(context)
    private val locationRequest = LocationRequest().apply {
        numUpdates = 1
        priority = LocationRequest.PRIORITY_HIGH_ACCURACY
    }

    override suspend fun getLocation(): LatLng = suspendCoroutine {
        val locationCallback = object : LocationCallback() {
            override fun onLocationResult(result: LocationResult) {
                result.lastLocation.run {
                    val latLng = latitude at longitude
                    it.resume(latLng)
                }

                fusedLocationProviderClient.removeLocationUpdates(this)
            }
        }

        try {
            fusedLocationProviderClient.requestLocationUpdates(locationRequest, locationCallback, Looper.myLooper())
        } catch (e: SecurityException) {
            throw NoLocationPermissionException()
        }
    }
}

但在尝试请求新位置时，出现以下异常：

java.lang.IllegalStateException: Can't create handler inside thread that has not called Looper.prepare()

但是，如果我调用 Looper.prepare() （最终调用 Looper.quit() ）是不是意味着我只能调用该函数一次？

感谢任何帮助。

Answer 1

您的coroutineContext 设置错误。你应该有

override val coroutineContext = Dispatchers.MAIN + job

如果您需要 IO 调度程序，请明确要求：

withContext(Dispatchers.IO) { ... blocking IO code ... }

要暂停协程，请调用suspendCancellableCoroutine，否则您将无法从结构化并发中获得任何好处。

另外一个细节，不要在suspendCancellableCoroutine块的it.resume之后写任何代码。如果调度程序选择立即恢复协程，在 resume 调用中，该代码将不会执行，直到协程的所有代码都已运行（或至少直到下一个暂停点）。

override fun onLocationResult(result: LocationResult) {
    fusedLocationProviderClient.removeLocationUpdates(this)
    it.resume(result.lastLocation.run { latitude at longitude })
}

Answer 2

private val locationRequestGPS by lazy {
    LocationRequest.create()
            .setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY)
            .setNumUpdates(1)
            .setExpirationDuration(1000)
}

private val locationRequestNETWORK by lazy {
    LocationRequest.create()
            .setPriority(LocationRequest.PRIORITY_LOW_POWER)
            .setNumUpdates(1)
            .setExpirationDuration(1000)
}



suspend fun getLocation(context: Context, offsetMinutes: Int = 15): Location? = suspendCoroutine { task ->
    val ctx = context.applicationContext
    if (!ctx.isPermissionValid(Manifest.permission.ACCESS_COARSE_LOCATION)
            && !ctx.isPermissionValid(Manifest.permission.ACCESS_FINE_LOCATION)) {
        task.resume(null)
    } else {
        val manager = ctx.getSystemService(Context.LOCATION_SERVICE) as LocationManager
        if (!LocationManagerCompat.isLocationEnabled(manager)) {
            task.resume(null)
        } else {
            val service = LocationServices.getFusedLocationProviderClient(ctx)
            service.lastLocation
                    .addOnCompleteListener { locTask ->
                        if (locTask.result == null || System.currentTimeMillis() - locTask.result!!.time > offsetMinutes.minute) {
                            GlobalScope.launch(Dispatchers.Main) {
                                task.resume(locationRequest(manager, service))
                            }
                        } else {
                            task.resume(locTask.result)
                        }

                    }
        }
    }
}

suspend fun getLocationLast(context: Context): Location? = suspendCoroutine { task ->
    val ctx = context.applicationContext
    if (!ctx.isPermissionValid(Manifest.permission.ACCESS_COARSE_LOCATION)
            && !ctx.isPermissionValid(Manifest.permission.ACCESS_FINE_LOCATION)) {
        task.resume(null)
    } else {
        if (!LocationManagerCompat.isLocationEnabled(ctx.getSystemService(Context.LOCATION_SERVICE) as LocationManager)) {
            task.resume(null)
        } else {
            LocationServices.getFusedLocationProviderClient(ctx)
                    .lastLocation
                    .addOnCompleteListener { locTask ->
                        task.resume(locTask.result)
                    }
        }

    }
}

suspend fun locationRequest(locationManager: LocationManager, service: FusedLocationProviderClient): Location? = suspendCoroutine { task ->
    val callback = object : LocationCallback() {
        override fun onLocationResult(p0: LocationResult?) {
            service.removeLocationUpdates(this)
            task.resume(p0?.lastLocation)
        }
    }

    when {
        locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER) -> {
            service.requestLocationUpdates(locationRequestGPS, callback, Looper.getMainLooper())
        }
        locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER) -> {
            service.requestLocationUpdates(locationRequestNETWORK, callback, Looper.getMainLooper())
        }
        else -> {
            task.resume(null)
        }
    }
}

Answer 3

通过使用suspendCoroutine，您可以在运行时调用挂起函数的调度程序上调用提供的代码。由于大多数调度程序不在 Looper 线程上运行（几乎只有 Dispatchers.MAIN 运行），所以对 Looper.myLooper() 的调用失败。

文档说您可以将 Looper.myLooper() 替换为 null 以在未指定的线程上调用回调。然后，内置的协程调度程序将确保将其路由到正确的线程以恢复执行。

编辑：您可能需要调用it.intercepted().resume(latLng) 以确保将结果分派到正确的线程。我不完全确定 suspendCoroutine 延续是否默认被拦截。

此外，您无需调用fusedLocationProviderClient.removeLocationUpdates(this)，因为您已经将LocationRequest 中的更新次数设置为1。