I've used same technique in one of my side projects, and when resuming the listening activity, sometimes ConflatedBroadcastChannel fires it's recent value, causing the execution of flatMapLatest body without any change.
I think this is happening while the system collects the garbage since I can reproduce this issue by calling System.gc() from another activity.
MainActivity.kt
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val viewModel = ViewModelProvider(this).get(MainViewModel::class.java)
val tvCount = findViewById<TextView>(R.id.tv_count)
viewModel.count.observe(this, Observer {
tvCount.text = it
Toast.makeText(this, "Incremented", Toast.LENGTH_LONG).show();
})
findViewById<Button>(R.id.b_inc).setOnClickListener {
viewModel.increment()
}
findViewById<Button>(R.id.b_detail).setOnClickListener {
startActivity(Intent(this, DetailActivity::class.java))
}
}
}
MainViewModel.kt
class MainViewModel : ViewModel() {
companion object {
val TAG = MainViewModel::class.java.simpleName
}
class IncrementRequest
private var tempCount = 0
private val requestChannel = ConflatedBroadcastChannel<IncrementRequest>()
val count = requestChannel
.asFlow()
.flatMapLatest {
tempCount++
Log.d(TAG, "Incrementing number to $tempCount")
flowOf("Number is $tempCount")
}
.conflate()
.asLiveData()
fun increment() {
requestChannel.offer(IncrementRequest())
}
}
DetailActivity.kt
class DetailActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_detail)
val button = findViewById<Button>(R.id.b_gc)
val timer = object : CountDownTimer(5000, 1000) {
override fun onFinish() {
button.isEnabled = true
button.text = "CALL SYSTEM.GC() AND CLOSE ACTIVITY"
}
override fun onTick(millisUntilFinished: Long) {
button.text = "${TimeUnit.MILLISECONDS.toSeconds(millisUntilFinished)} second(s)"
}
}
button.setOnClickListener {
System.gc()
finish()
}
timer.start()
}
}
In the advanced-coroutines-codelab sample, you've used
ConflatedBroadcastChannel
to watch thegrowZone
change.https://github.com/googlecodelabs/kotlin-coroutines/blob/b71b981f8354a92fb3ebda37eceb7461e783d0bf/advanced-coroutines-codelab/finished_code/src/main/java/com/example/android/advancedcoroutines/PlantListViewModel.kt#L91-L103
I've used same technique in one of my side projects, and when resuming the listening activity, sometimes
ConflatedBroadcastChannel
fires it's recent value, causing the execution offlatMapLatest
body without any change.I think this is happening while the system collects the garbage since I can reproduce this issue by calling
System.gc()
from another activity.MainActivity.kt
MainViewModel.kt
DetailActivity.kt
Here's the full source code : CoroutinesFlowTest.zip
Why is this happening? What am I missing?