长时间网络操作后使用主线程 [英] Use main thread after long network operation

问题描述

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

In my android app I has long network operation. After operation is finished I need to update my ui.

因此，需要在后台线程中执行较长的操作.

So as result long operation need to execute in background thread.

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

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?

I need to update my ui in main thread. So how I can fix this?

推荐答案

您可以像withContext(Dispatchers.Main)一样切换到主线程 当您用启动程序启动协程时，将在Dispatchers.Default上启动.最好是这样指定它:

You can switch to main thread like with the withContext(Dispatchers.Main) When you fire a coroutine with launch will start on the Dispatchers.Default. The best is to specify it like this:

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)
            }
        }

或者您可以只使用.postValue()而不是.value或.setValue()并忘记withContext().

Or you can just use .postValue() instead of .value or .setValue() and forget about withContext().

这篇关于长时间网络操作后使用主线程的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！