Flow builder and collect in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Flow in Kotlin?

A Flow is a type that can emit multiple values sequentially, like a stream of data that you can collect over time.

beginner

How do you create a simple Flow using the flow builder?

You use the flow { } builder and emit values inside it using emit(value).

beginner

What does the collect function do in Kotlin Flows?

collect gathers the emitted values from a Flow and lets you handle each value as it arrives.

intermediate

Why is collect a suspending function?

Because collecting values from a Flow can take time, collect suspends the coroutine until all values are received or the flow completes.

beginner

Show a simple example of a Flow that emits numbers 1 to 3 and collects them.

import kotlinx.coroutines.flow.*
import kotlinx.coroutines.runBlocking

fun simpleFlow() = flow {
  for (i in 1..3) {
    emit(i)
  }
}

fun main() = runBlocking {
  simpleFlow().collect { value ->
    println("Received $value")
  }
}

What keyword is used to create a Flow in Kotlin?

A emit

B async

C flow

D launch

The flow builder is used to create a Flow in Kotlin.

Which function do you use to receive values from a Flow?

A collect

B emit

C launch

D runBlocking

collect is used to receive and handle values emitted by a Flow.

Why must collect be called from a coroutine or suspending function?

A Because it is a suspending function

B Because it blocks the thread

C Because it returns immediately

D Because it is a constructor

collect is suspending, so it must be called from a coroutine or another suspending function.

What does emit do inside a flow builder?

A Starts a coroutine

B Stops the Flow

C Collects values

D Sends a value to the Flow

emit sends a value to the Flow to be collected later.

Which of these is true about Kotlin Flows?

A They are synchronous streams

B They can emit multiple values asynchronously

C They emit only one value

D They do not support coroutines

Flows can emit multiple values asynchronously over time.

Explain how to create and collect values from a Kotlin Flow using the flow builder and collect function.

Think about how you start a flow, send values, and then receive them.

Describe why collecting from a Flow requires a coroutine or suspending function.

Consider what happens when data arrives over time.