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Weird Race condition with Channels and ViewModel/LiveData
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ext.kotlin_version = '1.3.41' | |
dependencies { | |
implementation fileTree(dir: 'libs', include: ['*.jar']) | |
implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version" | |
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.2.2' | |
implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.2.2' | |
implementation 'androidx.core:core-ktx:1.1.0-rc02' | |
implementation 'androidx.appcompat:appcompat:1.1.0-rc01' | |
implementation 'androidx.activity:activity-ktx:1.1.0-alpha01' | |
implementation 'androidx.lifecycle:lifecycle-livedata-ktx:2.1.0-rc01' | |
implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.1.0-rc01' | |
implementation 'androidx.lifecycle:lifecycle-extensions:2.1.0-rc01' | |
} |
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class MainActivity : AppCompatActivity(R.layout.activity_main) { | |
private val viewModel by viewModels<MainViewModel>() | |
override fun onCreate(savedInstanceState: Bundle?) { | |
super.onCreate(savedInstanceState) | |
viewModel.liveData.observe(this, Observer { | |
Log.d("MAIN", "Display $it in view") | |
textView.text = it | |
}) | |
button.setOnClickListener { viewModel.onClick() } | |
} | |
} | |
class MainViewModel : ViewModel() { | |
private val chan = ConflatedBroadcastChannel(Counter(0, "loaded")) | |
val liveData = chan.toLiveData(viewModelScope) { | |
Log.d("MAIN", "sending $it to view") | |
"counter: $it" | |
} | |
init { | |
viewModelScope.launch(Dispatchers.IO) { | |
var lastCounterCount: Int? = null | |
var job: Job? = null | |
chan.consumeEach { | |
Log.d("MAIN", "New counter in worker $it") | |
if (it.counter != lastCounterCount) { | |
lastCounterCount = it.counter | |
job?.cancel() | |
Log.d("MAIN", "new count, new job") | |
job = viewModelScope.launch(Dispatchers.IO) { | |
Log.d("MAIN", "loading for ${it.counter}") | |
chan.send(chan.value.copy(state = "loading")) | |
delay(2000) | |
Log.d("MAIN", "finish loading for ${it.counter}") | |
chan.send(chan.value.copy(state = "loaded")) | |
} | |
job?.invokeOnCompletion { Log.d("MAIN", "job cancelled $it") } | |
} else { | |
Log.d("MAIN", "Same count") | |
} | |
} | |
} | |
} | |
fun onClick() { | |
viewModelScope.launch(Dispatchers.IO) { | |
val currentCounter = chan.value | |
chan.send(currentCounter.copy(counter = currentCounter.counter + 1)) | |
} | |
} | |
} | |
data class Counter(val counter: Int, val state: String) | |
fun <I, O> ConflatedBroadcastChannel<I>.toLiveData( | |
scope: CoroutineScope, | |
block: suspend (I) -> O | |
): LiveData<O> { | |
var currentSubscription: ReceiveChannel<I>? = null | |
return object : MutableLiveData<O>() { | |
override fun onActive() { | |
currentSubscription = openSubscription() | |
scope.launch(Dispatchers.IO) { | |
currentSubscription?.consumeEach { | |
postValue(block(it)) | |
} | |
}.invokeOnCompletion { currentSubscription?.cancel() } | |
} | |
override fun onInactive() { | |
currentSubscription?.cancel() | |
currentSubscription = null | |
} | |
} | |
} |
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