Question

我是协程新手，我想知道是否可以从以下代码的coroutineScope（GlobalScope）切换到UI范围。我的问题是，协程启动体内的步骤必须在辅助线程中执行，否则侦听器通知必须在ui线程中执行，以避免在我的活动代码中调用runOnUiThread。

override suspend fun startRent(name: String, bikeMode: BikeMode, listener: StartRentListener) {
        var bleDevice : RxBleDevice
        val scanFilter: ScanFilter = ScanFilter.Builder().setDeviceName(name).build()
        val scanSettings: ScanSettings = ScanSettings.Builder().build()

        val job = GlobalScope.launch {
            try {
                bleDevice = rxBleClient.scanBleDevicesExt(rxBleClient, scanSettings, scanFilter)
                val bleConnection = bleDevice.establishConnectionExt()
                // write handshake
                connectionManager.writeHandshake(bleDevice, bleConnection)
                // open lock
                openLock(bleDevice, bikeMode, bleConnection)
                // getting user position
                apiHelper.sendLockRequest(bleDevice.name, getPosition())
                bleDevice.disconnect()
                // this should be called on main thread once all the previous operations are finished
                listener.onSuccess()
            } catch (e: Exception) {
                listener.onError(e)
            }
        }
        job.join()
    }

我当前活动代码的摘录：

bikeAccessClient.startRent(bikeBLEName, BikeMode.HYBRID, object :
                    StartRentListener {
                    override fun onSuccess() {
                        runOnUiThread {
                            // UI update here
                        }
                    }

Answer 1

您可以使用withContext(Dispatchers.UI) {..}函数与另一个Coroutine Dispatcher一起执行部分代码。

kotlinx.coroutines.android包含Dispatchers.UI函数的定义，并且已与Android UI正确集成。

在您的代码中使用显式分派器非常容易出错。取而代之，我建议在设计代码时减少明确的要求。

我会这样写：

fun uiActionHandlerToStartTheProcess() {
  launch(Dispatchers.Main) {
     val result = startRent(...) // no callback here, suspend function

     //UI Update Here
   }
}
suspend fun CoroutineScope.startRent() : SomeResultOfWork {
   //that function offloads the execution to a IO (aka brackground) thread
   return withContext(Dispatchers.IO){
     //here goes your code from `startRent`
     //use `suspendCancellableCoroutine {cont -> .. }` if you need to handle callbacks from it

     SomeResultOfWork()
   }

launch(Dispatchers.Main){..}块中的代码在UI线程中执行。对startRent暂停函数的调用将在UI线程中暂停执行。 startRent准备好了（来自后台线程）的回复后，它将继续执行（由Dispatchers.Main完成并等效于runOnUiThread {...}），并从右螺纹

在协程中切换到UI上下文

1 个答案: