Kotlin 等待与协程的异步

Question

I would like to open a new activity when phoneViewModel and ScanViewModel are instantiated. They are instantiated by calling an async function InitialRead(). I'm logging each step, atm they are logged as done3 => done2 => done1

I would like to have them in this order: done1 => done2 => done3

I have following code:

class MainBusinessActivity : AppCompatActivity() {

private lateinit var scanViewModel: ScanViewModel
private lateinit var phoneViewModel: PhoneViewModel

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

private fun startEntitySetListActivity() = GlobalScope.async {
    val sapServiceManager = (application as SAPWizardApplication).sapServiceManager
    sapServiceManager?.openODataStore {
        phoneViewModel =  ViewModelProvider(this@MainBusinessActivity).get(PhoneViewModel::class.java).also {it.initialRead{Log.e("done", "done1")}}
        scanViewModel = ViewModelProvider(this@MainBusinessActivity).get(ScanViewModel::class.java).also {it.initialRead{Log.e("done", "done2")}}
    }
}

override fun onResume() {
    super.onResume()
    //startEntitySetListActivity()
    runBlocking {
        startEntitySetListActivity().await()
        val intent = Intent(this@MainBusinessActivity, HomeActivity::class.java)
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_CLEAR_TASK)
        Log.e("done", "done3")
        startActivity(intent)
    }
}

}

What am I doing wrong? Can someone correct my code?

Answer 1

Never use runBlocking in an Android app. runBlocking completely defeats the purpose of using coroutines, and can lead to an ANR. You also probably should never use GlobalScope , which leads to UI leaks. You might possibly need it for some kind of long-running task that doesn't make sense to put in a service but doesn't have dependency on any UI components, but I can't think of any examples

You also shouldn't be instantiating your ViewModels in the background. That should be done in onCreate() .

Make this function a suspend function, and it can break down the two tasks in the background simultaneously before returning.

Start your coroutine with lifecycleScope .

Assuming sapServiceManager?.openODataStore is an asynchronous task that takes a callback, you will need to wrap it in suspendCoroutine .

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main_business)
    phoneViewModel = ViewModelProvider(this@MainBusinessActivity).get(PhoneViewModel::class.java)
    scanViewModel = ViewModelProvider(this@MainBusinessActivity).get(ScanViewModel::class.java)
}

private suspend fun startEntitySetListActivity() = coroutineScope {
    val sapServiceManager = (application as SAPWizardApplication).sapServiceManager
    sapServiceManager ?: return
    suspendCoroutine<Unit> { continuation ->
        sapServiceManager.openODataStore { continuation.resume(Unit) }
    }
    listOf(
        launch {
            phoneViewModel.initialRead{Log.e("done", "done1")}
        },
        launch {
            scanViewModel.initialRead{Log.e("done", "done2")}
        }
    ).joinAll()
}

override fun onResume() {
    super.onResume()
    lifecycleScope.launch {
        startEntitySetListActivity()
        val intent = Intent(this@MainBusinessActivity, HomeActivity::class.java)
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_CLEAR_TASK)
        Log.e("done", "done3")
        startActivity(intent)
    }
}