Kotlin Flow and Flow Builders

In this series of articles , we will discuss about Kotlin flows and in this article we will discuss about Flows and Flow Builders

Code gist can be found in https://gist.github.com/vprabhu/cf5f6407516f0bc97d764c7a9961e3cd

Whats is Flow ?

Already we know that suspend function asynchronously returns a single value .

Flows can return multiple asynchronously computed values

Flow Builders

we can build a flow using one of the following ways

<T> flowOf(value : T)

Creates a flow from fixed set of any values which is it can emit both a single type value and multiple data type values as follows

/**
 * flowOf() -> Create a flow from fixed set of values
 */
val singleValueFlow = flowOf<Int>(578943).collect { value ->
    println("Emitted Value : $value") // output : 578943
}

/*
 * flowOf() -> creating a flow with multiple data types
 */
val multiValueFlows = flowOf<Any>(23, 2.90, false, "Android 1.0", 09.2008)

multiValueFlows.collect { value ->
    println("multiValueFlows ->  Emitted Value : $value")
    //output :
    //multiValueFlows ->  Emitted Value : 23
    //multiValueFlows ->  Emitted Value : 2.9
    //multiValueFlows ->  Emitted Value : false
    //multiValueFlows ->  Emitted Value : Android 1.0
    //multiValueFlows ->  Emitted Value : 9.2008
}

2.<T> Iterable<T>.asFlow()

Extension function for various types of iterators to convert them into flows and it cal also emit multiple data type values

/**
 * asFlow() -> extension function on various types to convert them into Flows
 */
listOf("A", "B", "C", 4, true, 90.89).asFlow().collect { value ->
    println("AsFlow Emitted Value : $value")
    //output :
    //AsFlow Emitted Value : A
    //AsFlow Emitted Value : B
    //AsFlow Emitted Value : C
    //AsFlow Emitted Value : 4
    //AsFlow Emitted Value : true
    //AsFlow Emitted Value : 90.89
}

3.<T> flow(block: suspend <T>.() -> Unit)

Creates a flow from suspendable code block given

/**
 * flow {..} -> creates a flow from the suspendable block given
 */
flow {
    kotlinx.coroutines.delay(2000)
    emit(890)
    emit(returnSomething())
}.collect { value ->
    println("flow {} Emitted Value : $value")
    // output :
    // flow {} Emitted Value : 890
    // flow {} Emitted Value : 340
}

fun returnSomething(): Int {
    return 340
}

Important Considerations:

Simply put

collect{ .. } -> Terminal flow operator that collects the given flow

emit() -> Collects the value emitted by the upstream.

we will discuss this is further articles

Please leave your comments to improve.

Happy and Enjoy coding

Vignesh Prabhu