kotlin 协程抛出 java.lang.IllegalStateException：已经恢复，但得到了值位置

Question

总的来说，我对 Kotlin 协程和 Android 开发很陌生。在尝试了解它是如何工作的时，我遇到了一个似乎无法解决的错误。

从基本活动中，我尝试连接到 googleApiClient。权限没问题。我希望使用 kotlin 协程以直接方式从 LocationManager 获取位置更新，以便稍后使用此 Location 对象。我第一次在模拟器中改变我的位置时它工作正常，第二次我改变我的位置时，它崩溃了，异常如下：

FATAL EXCEPTION: main
    Process: com.link_value.eventlv, PID: 32404
    java.lang.IllegalStateException: Already resumed, but got value Location[gps 48.783000,2.516180 acc=20 et=+59m16s372ms alt=0.0 {Bundle[mParcelledData.dataSize=40]}]
    at kotlinx.coroutines.experimental.AbstractContinuation.resumeImpl(AbstractContinuation.kt:79)
    at kotlinx.coroutines.experimental.AbstractContinuation.resume(AbstractContinuation.kt:72)
    at com.link_value.eventlv.View.Create.NewEventLvActivity$await$2$1.onLocationChanged(NewEventLvActivity.kt:100)
    at android.location.LocationManager$ListenerTransport._handleMessage(LocationManager.java:297)
    at android.location.LocationManager$ListenerTransport.-wrap0(LocationManager.java)
    at android.location.LocationManager$ListenerTransport$1.handleMessage(LocationManager.java:242)
     at android.os.Handler.dispatchMessage(Handler.java:102)
     at android.os.Looper.loop(Looper.java:154)
     at android.app.ActivityThread.main(ActivityThread.java:6077)
     at java.lang.reflect.Method.invoke(Native Method)
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)



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

    askForUserLocation()
    val locationManager = this.getSystemService(Context.LOCATION_SERVICE) as LocationManager
    val presenter = CreateEventPresenterImpl(this@NewEventLvActivity)

    googleApiClient = GoogleApiClient.Builder(this@NewEventLvActivity)
            .enableAutoManage(this /* FragmentActivity */,
                    this /* OnConnectionFailedListener */)
            .addApi(Places.GEO_DATA_API)
            .addConnectionCallbacks(this)
            .build()
}
override fun onConnected(p0: Bundle?) {
    val locationManager = this.getSystemService(Context.LOCATION_SERVICE) as LocationManager
    input_address.addTextChangedListener(object: TextWatcher{
        override fun afterTextChanged(p0: Editable?) {
        }

        override fun beforeTextChanged(p0: CharSequence?, p1: Int, p2: Int, p3: Int) {
        }

        override fun onTextChanged(query: CharSequence?, p1: Int, p2: Int, p3: Int) {
            if (query.toString().length >= 4) {
                launch(UI) {
                    val locationUpdated = locationManager.await(LocationManager.GPS_PROVIDER)
                    input_name.text = Editable.Factory.getInstance().newEditable(locationUpdated.toString())
                }
            }
        }
    })
}

private suspend fun LocationManager.await(locationProvider: String): Location? = suspendCoroutine { cont ->
    try {
        requestLocationUpdates(locationProvider, 0, 0.toFloat(), object : LocationListener {
            override fun onStatusChanged(p0: String?, p1: Int, p2: Bundle?) {
            }

            override fun onProviderEnabled(p0: String?) {
            }

            override fun onProviderDisabled(p0: String?) {
                cont.resumeWithException(UnknownLocationException())
            }

            override fun onLocationChanged(location: Location?) {
                cont.resume(location)
            }
        })
    } catch (ex: SecurityException) {
        cont.resumeWithException(ex)
    }
}

就好像 Kotlin 使用相同的 Continuation。我不知道我做错了什么以及为什么它第二次崩溃。有人可以启发我。提前谢谢。

Answer 1

根据文档，可以仅恢复一次 Continuation。第二份简历将抛出IllegalStateException“已经恢复，但收到 $proposedUpdate”消息。您可以添加额外的检查continuation.isActive以防止出现此异常。最好将 Channels 用于多个回调，例如位置更新。

Answer 2

您可以使用此功能来防止此异常。

import kotlinx.coroutines.CancellableContinuation
import kotlin.coroutines.Continuation
import kotlin.coroutines.resume

inline fun <T> Continuation<T>.safeResume(value: T, onExceptionCalled: () -> Unit) {
    if (this is CancellableContinuation) {
      if (isActive)
        resume(value)
      else
        onExceptionCalled()
    } else throw Exception("Must use suspendCancellableCoroutine instead of suspendCoroutine")
}

suspendCoroutine请注意，如果您使用而不是 ，我将引发异常suspendCancellableCoroutine。

用法：

suspend fun getId() : Result<String> = suspendCancellableCoroutine { continuation ->

   ...

   continuation.safeResume(Result.success(adjustID)) { Timber.e("Job has already done") }
}

Answer 3

我最近在我们的项目中使用的第 3 方 API 之一遇到了这个问题。问题仅在 API 方面，因为在底层实现中unsubscribe多次调用回调，并且方法没有立即从 API 中删除回调。

所以，我选择的方法只是简单地添加一个布尔标志。虽然，它可以用 KotlinFlow.mapLatest/collectLatest左右以更优雅的方式解决。

suspend fun singularContentUpdate(): Data =
    suspendCancellableCoroutine { continuation ->
        var resumed = false

        val callback = object : Callback {
            override fun onDataReady(d: Data) {
                api.unsubscribe(this)

                if (!resumed) {
                    continuation.resume(d)
                    resumed = true
                }
            }
        }

        continuation.invokeOnCancellation {
            api.unsubscribe(callback)
        }

        api.subscribe(subscriber)

        api.refresh()
    }