name: 'Android Basics: Introduction to Room and Flow issue template' about: 'Cannot access database on the main thread.' title: 'Android Basics: Introduction to Room and Flow' labels: '' assignees: ''

URL of codelab https://developer.android.com/codelabs/basic-android-kotlin-training-intro-room-flow?continue=https%3A%2F%2Fdeveloper.android.com%2Fcourses%2Fpathways%2Fandroid-basics-kotlin-unit-5-pathway-1%23codelab-https%3A%2F%2Fdeveloper.android.com%2Fcodelabs%2Fbasic-android-kotlin-training-intro-room-flow#7

In which task and step of the codelab can this issue be found? 8 - 4. (really 9, also bad numbers on indexes)Finally, to update a list view, call submitList(), passing in the list of bus stops from the view model 8- 11 Then configure the recycler view in onCreate(). This time you just need to pass in an empty block (function) with {}. You don't actually want anything to happen when rows on this screen are tapped.

Describe the problem these lines code busStopAdapter.submitList(viewModel.scheduleForStopName()) busStopAdapter.submitList(viewModel.fullSchedule()) java.lang.IllegalStateException: Cannot access database on the main thread since it may potentially lock the UI for a long period of time. no sure but need to run it on corouitines? (only that way i make it work) also the onCreate() of 8 - 11 (onViewCreated)

Steps to reproduce? complete the codelabs to the poit 8 inclusive 6/12 inclusive

Versions _Android Studio version:_4.2.1 API version of the emulator: 28

Additional information

In the instructions for changing the FullScheduleFragment it says:

Replace the line.

busStopAdapter.submitList(viewModel.fullSchedule())

With this code that uses the flow returned from fullSchedule().

lifecycle.coroutineScope.launch {
   viewModel.fullSchedule().collect() {
       busStopAdapter.submitList(it)
   }
}

When it should say to replace the entire GlobalScope function. The same goes for the StopScheduleFragment section

Inside onCreate() in the StopScheduleFragment, busStopAdapter.submitList(viewModel.scheduleByStopName()) should be called instead as : busStopAdapter.submitList(viewModel.scheduleByStopName(stopName)) I am not sure but most probably this is correct!

Create list adapter at the end "Now that you've set up the adapter, you're done integrating Room into the Bus Schedule app. Take a moment to run the app and you should see a list of arrival times. Tapping on a row should navigate to the detail screen." Got error

FATAL EXCEPTION: main
    Process: com.example.busschedule, PID: 22917
    java.lang.IllegalStateException: Cannot access database on the main thread since it may potentially lock the UI for a long period of time.

in main branch

        lifecycle.coroutineScope.launch {
            viewModel.fullSchedule().collect() {
                busStopAdapter.submitList(it)
            }
        }

But in course there is none

        recyclerView.adapter = busStopAdapter
        busStopAdapter.submitList(viewModel.fullSchedule())

soz you have to use something like this:

        lifecycleScope.launch {
            busStopAdapter.submitList(viewModel.fullSchedule())
        }

and in viewModel sort of:

    suspend fun fullSchedule(): List<Schedule> = withContext(Dispatchers.IO) {
        scheduleDao.getAll()
    }

Whenever you try to download the starter app in GitHub, the main branch is downloaded instead. All the changes are already done for the codelab. The only way I could get around it was to copy and change the URL to say "starter" rather than "main."

This example would be improved with more explanation for each new section of code, especially on Step 8, to say why each step is needed. Currently it's just saying effectively "write this code, then write this code, then this, etc.." and the application may work at the end but without enough clarity to really explain what is happening. This is based on having worked through the previous tutorials on view models etc.

In the "Define the ViewModel" step, there is a sentence that reads "As the ViewModel class BusScheduleViewModel needs from is meant to be lifecycle aware, it should be instantiated by an object that can respond to lifecycle events."

Should this instead be? "As the ViewModel class BusScheduleViewModel is meant to be lifecycle aware, it should be instantiated by an object that can respond to lifecycle events."

It seems as if there's a typo in step 6 of the "Introduction to Room and Flow" Codelab.

"As the ViewModel class BusScheduleViewModel needs from is meant to be lifecycle aware, it should be instantiated by an object that can respond to lifecycle events."

Followed instructions as provided. App crashes while testing the result of Step 8.

I compared my code to the main code and apart from the Flow introductions in Step 9 is the same.

Error given by the debugger is:

E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.busschedule, PID: 26884 java.lang.IllegalStateException: Cannot access database on the main thread since it may potentially lock the UI for a long period of time. at androidx.room.RoomDatabase.assertNotMainThread(RoomDatabase.java:385) at androidx.room.RoomDatabase.query(RoomDatabase.java:441) at androidx.room.util.DBUtil.query(DBUtil.java:83) at com.example.busschedule.database.schedule.ScheduleDao_Impl.getAll(ScheduleDao_Impl.java:29) at com.example.busschedule.viewmodel.BusScheduleViewModel.fullSchedule(BusScheduleViewModel.kt:10) at com.example.busschedule.FullScheduleFragment$onViewCreated$1.invokeSuspend(FullScheduleFragment.kt:77) at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33) at kotlinx.coroutines.internal.DispatchedContinuationKt.resumeCancellableWith(DispatchedContinuation.kt:342) at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable(Cancellable.kt:30) at kotlinx.coroutines.intrinsics.CancellableKt.startCoroutineCancellable$default(Cancellable.kt:27) at kotlinx.coroutines.CoroutineStart.invoke(CoroutineStart.kt:109) at kotlinx.coroutines.AbstractCoroutine.start(AbstractCoroutine.kt:158) at kotlinx.coroutines.BuildersKt__Builders_commonKt.launch(Builders.common.kt:56) at kotlinx.coroutines.BuildersKt.launch(Unknown Source:1) at kotlinx.coroutines.BuildersKt__Builders_commonKt.launch$default(Builders.common.kt:49) at kotlinx.coroutines.BuildersKt.launch$default(Unknown Source:1) at com.example.busschedule.FullScheduleFragment.onViewCreated(FullScheduleFragment.kt:76) at androidx.fragment.app.Fragment.performViewCreated(Fragment.java:2987) at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:546) at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:282) at androidx.fragment.app.FragmentStore.moveToExpectedState(FragmentStore.java:112) at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1647) at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:3128) at androidx.fragment.app.FragmentManager.dispatchViewCreated(FragmentManager.java:3065) at androidx.fragment.app.Fragment.performViewCreated(Fragment.java:2988) at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:546) at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:282) at androidx.fragment.app.FragmentStore.moveToExpectedState(FragmentStore.java:112) at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1647) at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:3128) at androidx.fragment.app.FragmentManager.dispatchActivityCreated(FragmentManager.java:3072) at androidx.fragment.app.FragmentController.dispatchActivityCreated(FragmentController.java:251) at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:501) at androidx.appcompat.app.AppCompatActivity.onStart(AppCompatActivity.java:246) at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1425) at android.app.Activity.performStart(Activity.java:7825) at android.app.ActivityThread.handleStartActivity(ActivityThread.java:3294) at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:221) at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:201) at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:173) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:97) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) at android.os.Handler.dispatchMessage(Handler.java:107) at android.os.Looper.loop(Looper.java:214) at android.app.ActivityThread.main(ActivityThread.java:7356) at java.lang.reflect.Method.invoke(Native Method) E/AndroidRuntime: at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

Just letting you know that the package database.schedule doesn't exist in this project. There is only a database package located in the assets directory and no subdirectory or package named schedule within it. Should we just create a directory within database called schedule or create a new package altogether within java called database.schdule?

These are the instructions I'm referring to:

"Note that the SQL types used in the database are actually INTEGER for Int and TEXT for String. When working with Room, however, you should only be concerned with the Kotlin types when defining your model classes. Mapping the data types in your model class to the ones used in the database is handled automatically.

To create an entity for the "schedule" table, in the database.schedule package, create a new file called Schedule.ktand define a data class called Schedule."

In section 4: Create an Entitiy, it is stated, "To create an entity for the "schedule" table, in the database.schedule package, create a new file called Schedule.kt and define a data class called Schedule."

There is not a "database.schedule" package within the Project Manager. My assumption is that it is referencing "assets/database", but this needs to be clarified.

I downloaded the project from the "main" branch, I open it and try to compile it without changing anything - it says that there is an error in ActivityMain, R.id.nav_host_fragment is highlighted.

This whole Kotlin thing went from 0 to a 100 real quick. Every lesson until now was understandable, even if I didn't understand something that I wrote, a quick Googleing job would help, but things happening in here are high above my knowledge, knowledge that I gained from previous classes. Description of steps is very poor, the only thing I can do is a lot of retyping and almost no understanding of what I'm doing.

"FullScheduleFragmentDirections" showing error as Unresolved reference

and " .navigate(action)" as Overload resolution ambiguity

But the project builds successfully.

private val viewModel: BusScheduleViewModel by activityViewModels { BusScheduleViewModelFactory( (activity?.application as BusScheduleApplication).database.scheduleDao() ) }

Missing from starter code. No mention in the tutorial. Would be nice to get an explanation, that would complete this tutorial for me. 


nevermind, found it here https://developer.android.com/codelabs/basic-android-kotlin-training-intro-room-flow?continue=https%3A%2F%2Fdeveloper.android.com%2Fcourses%2Fpathways%2Fandroid-basics-kotlin-unit-5-pathway-1%23codelab-https%3A%2F%2Fdeveloper.android.com%2Fcodelabs%2Fbasic-android-kotlin-training-intro-room-flow#7