Question

在我的android应用中，我的网络操作时间很长。操作完成后，我需要更新我的用户界面。

因此，需要在后台线程中执行较长的操作。

摘要：

private val isShowProgressLiveData = MutableLiveData<Boolean>()

  // launch a new coroutine in background and continue
GlobalScope.launch() {
            try {
                val executeOperations = OperationFactory.createExecuteTraderOperation(Trader.Operation.CREATE, base, quote)
                val response: Response<Void> = executeOperations.await()
                if (response.isSuccessful) { 
                    isShowProgressLiveData.value = false
                    isForwardToTradersLiveData.value = true
                } else {
                    Debug.w(TAG, "doClickStart_error")
                }
            } catch (e: Throwable) {
                Debug.e(TAG, "doClickStart_network error: $e.message", e)
            }
        }

但我在

上遇到错误

isShowProgressLiveData.value = false

错误消息：

java.lang.IllegalStateException: Cannot invoke setValue on a background thread
    at androidx.lifecycle.LiveData.assertMainThread(LiveData.java:461)
    at androidx.lifecycle.LiveData.setValue(LiveData.java:304)
    at androidx.lifecycle.MutableLiveData.setValue(MutableLiveData.java:50)
    at com.myoperation.AddTraderViewModel$doClickStart$3.invokeSuspend(AddTraderViewModel.kt:55)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(Dispatched.kt:238)
    at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:594)
    at kotlinx.coroutines.scheduling.CoroutineScheduler.access$runSafely(CoroutineScheduler.kt:60)
    at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:742)

我需要在主线程中更新ui。那我该如何解决呢？

Answer 1

您可以像withContext(Dispatchers.Main)那样切换到主线程当您启动协同程序时，将在Dispatchers.Default上启动。最好是这样指定它：

GlobalScope.launch(Dispatchers.IO) {
            try {
                val executeOperations = OperationFactory.createExecuteTraderOperation(Trader.Operation.CREATE, base, quote)
                val response: Response<Void> = executeOperations.await()
                if (response.isSuccessful) { 
                  withContext(Dispatchers.Main){ //switched to Main thread
                    isShowProgressLiveData.value = false
                    isForwardToTradersLiveData.value = true
                 }
                } else {
                    Debug.w(TAG, "doClickStart_error")
                }
            } catch (e: Throwable) {
                Debug.e(TAG, "doClickStart_network error: $e.message", e)
            }
        }

Answer 2

当您尝试执行

时，您仍处于后台线程中

isShowProgressLiveData.value = false

您可以执行以下操作：

GlobalScope.launch() {
        try {
            val executeOperations = OperationFactory.createExecuteTraderOperation(Trader.Operation.CREATE, base, quote)
            val response: Response<Void> = executeOperations.await()
            if (response.isSuccessful) { 


                YourActivity.runOnUiThread(object:Runnable() {

                override fun run() {
                isShowProgressLiveData.value = false
                isForwardToTradersLiveData.value = true
                    }


             }
            } else {
                Debug.w(TAG, "doClickStart_error")
            }
        } catch (e: Throwable) {
            Debug.e(TAG, "doClickStart_network error: $e.message", e)
        }
    }

长时间网络操作后使用主线程

2 个答案: