Kotlin wait for async with coroutine

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?

Tenfour04 · Accepted Answer · 2020-10-21 19:16:01Z

2

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)
    }
}

edited Oct 21, 2020 at 19:16

answered Oct 21, 2020 at 18:25

Tenfour04

95.1k14 gold badges125 silver badges181 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

axeldion Over a year ago

Thanks for your comment but I'm getting unresolved reference for launch and lifecycleScope. Do I need to declare them or import them?

Tenfour04 Over a year ago

Maybe you are missing the build dependency on androidx.fragment:fragment-ktx?

Tenfour04 Over a year ago

I was also missing the coroutineScope wrapper. Just fixed it above.

axeldion Over a year ago

Thanks, the only problem remaining is that my viewmodel must be instantiated inside the openODataStore{HERE}. Else I'm getting Cannot create instance of class PhoneViewModel

Tenfour04 Over a year ago

I don't understand what that class or function is, or how your ViewModel instantiation could require it when you are not passing anything to the ViewModel factory from that lambda.

|

Collectives™ on Stack Overflow

Kotlin wait for async with coroutine

1 Answer 1

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related