Kotlin Flow — Combine, Merge and Zip

Exploring the Power of Kotlin Flow: Combining, Merging, and Zipping Streams

This is part of the asynchronous flow series:

• Part 1 — Exploring Android LiveData Usages and Behaviors
• Part 2 — Introduction to Kotlin Flows and Channels
• Part 3 — Exploring Different Ways to Collect Kotlin Flow
• Part 4 — Convert Flow to SharedFlow and StateFlow
• Part 5 — Flow, SharedFlow, StateFlow Class Diagram
• Part 6 — Kotlin Flow — Combine, Merge and Zip

I have 2 flows here.

Flow1 emits int starting from 1 -> 1000 every 1 second.

private val flow1: Flow<Int> = flow {
    repeat(10000) { value ->
        delay(1000)
        Log.d(tag, "[Flow1]: emitting $value")
        emit(value)
    }
}

Flow 2 emits char from A to Z every 2 seconds.

private val flow2: Flow<Char> = flow {
    var value = 'A'
    while(true) {
        delay(2000)
        Log.d(tag, "[Flow2]: emitting $value")
        emit(value)
        if (value == 'Z') {
            value = 'A'
        } else {
            value += 1
        }
    }
}

Combine Flow

This combines flow1 and flow2 into combineFlow using the Flow.combine() extension function flow operator.

val combineFlow = flow1.combine(flow2) { flow1Value,flow2Value  ->
    "${flow1Value}_${flow2Value}"
}

The limitation of this Flow.combine() extension function is it is limited to combining 2 flows. To combine more than 2 flows, you can use combine() function directly which supports up to 5 flows.

val combineFlow = combine(flow1, flow2) { flow1Value, flow2Value ->
    "${flow1Value}_${flow2Value}"
}

To collect the flow, I use the LaunchedEffect() side effect for this demonstration purpose. The recommended way is either using collectAsStateWithLifeCylce()or repeatOnLifecycle(Lifecycle.State.STARTED), see here.

LaunchedEffect(true) {…