Flattening Flow: FlatMapConcat or FlattenConcat
When there is a flow of flows and we want the value from the inner flow, We can use the flattenConcat operator
Also the flatMapConcat is a combination of map + flattenConcat
Observe it uses a same co-routine to run synchronously one after another
Output
kotlinx.coroutines.flow.SafeFlow@2836a3c
kotlinx.coroutines.flow.SafeFlow@2bab3c5
kotlinx.coroutines.flow.SafeFlow@ba2c11a
kotlinx.coroutines.flow.SafeFlow@f3e544b
kotlinx.coroutines.flow.SafeFlow@83aee28Code
class FlattenFlowsDemoVm @Inject constructor(
@ApplicationContext private val context: Context,
) : ViewModel() {
private val rootScope = CoroutineScope(context = Dispatchers.IO)
/**
* Flow of integers
*/
fun generateIntegers() = flow {
repeat(100){
delay(1000)
emit(it)
}
}
/**
* Generate a flow of strings
*/
fun generateFlowOfStrings(value : Int) = flow {
val content = "Current string no -->$value"
println("<Emitted> -->$value")
emit(content)
}
fun flatMapConcatDemo() = rootScope.launch(CoroutineName("FlatMapConcatDemo")){
val result : Flow<Flow<String>> = generateIntegers()
.take(5)
.map {
generateFlowOfStrings(it)
}
result.collect{
println(it)
}
}
}Output
<Emitted> -->0
Current string no -->0 at the threadDefaultDispatcher-worker-1
<Emitted> -->1
Current string no -->1 at the threadDefaultDispatcher-worker-1
<Emitted> -->2
Current string no -->2 at the threadDefaultDispatcher-worker-1
<Emitted> -->3
Current string no -->3 at the threadDefaultDispatcher-worker-1
<Emitted> -->4
Current string no -->4 at the threadDefaultDispatcher-worker-1Code
class FlattenFlowsDemoVm @Inject constructor(
@ApplicationContext private val context: Context,
) : ViewModel() {
private val rootScope = CoroutineScope(context = Dispatchers.IO)
/**
* Flow of integers
*/
fun generateIntegers() = flow {
repeat(100){
delay(1000)
emit(it)
}
}
/**
* Generate a flow of strings
*/
fun generateFlowOfStrings(value : Int) = flow {
val content = "Current string no -->$value at the thread${Thread.currentThread().name}"
println("<Emitted> -->$value")
emit(content)
}
fun flatMapConcat() = rootScope.launch(CoroutineName("FlatMapConcatDemo")){
// Way-1
/* val result : Flow<Flow<String>> = generateIntegers()
.take(5)
.map {
generateFlowOfStrings(it)
}
result.flattenConcat().collect{
println(it)
}*/
//Way-2
generateIntegers()
.take(5)
.flatMapConcat {
generateFlowOfStrings(it)
}.collect{
println(it)
}
}
}