Flow context preservation in Kotlin - Mini Project: Build & Apply

Flow context preservation

📖 Scenario: You are building a simple Kotlin program that uses Flow to emit numbers. You want to understand how the context (like the dispatcher) is preserved when collecting the flow.

🎯 Goal: Create a Flow that emits numbers, configure a coroutine context variable, collect the flow preserving the context, and print the results.

📋 What You'll Learn

Create a Flow that emits numbers 1 to 3

Create a coroutine context variable using Dispatchers.Default

Collect the flow using flowOn to preserve the context

Print each emitted number inside the collector

💡 Why This Matters

🌍 Real World

Flows are used in Kotlin to handle streams of data asynchronously, such as user inputs, network responses, or sensor data.

💼 Career

Understanding flow context preservation is important for writing efficient and correct asynchronous Kotlin applications, especially in Android development and backend services.

1

Create a Flow emitting numbers 1 to 3

Create a Flow called numberFlow that emits the numbers 1, 2, and 3 using flow builder and emit.

Kotlin

# Create a Flow called numberFlow that emits 1, 2, and 3
// Your code here

Need a hint?

Use val numberFlow: Flow = flow { emit(1); emit(2); emit(3) } to create the flow.

2

Create a coroutine context variable

Create a variable called context and set it to Dispatchers.Default.

Kotlin

import kotlinx.coroutines.Dispatchers

// Create a variable called context and set it to Dispatchers.Default
// Your code here

Need a hint?

Use val context = Dispatchers.Default to create the context variable.

3

Collect the flow preserving the context

Use flowOn(context) on numberFlow and collect it inside a runBlocking block. Use collect with a lambda that takes value and prints it with println.

Kotlin

import kotlinx.coroutines.flow.collect
import kotlinx.coroutines.flow.flowOn
import kotlinx.coroutines.runBlocking

// Collect numberFlow with flowOn(context) inside runBlocking and print each value
// Your code here

Need a hint?

Use runBlocking { numberFlow.flowOn(context).collect { value -> println(value) } } to collect and print.

4

Print the collected values

Run the program and print the output of collecting numberFlow with flowOn(context). The output should be the numbers 1, 2, and 3 each on its own line.

Kotlin

// Run the program to print the collected values
// Your code here

Need a hint?

Run the program. You should see 1, 2, and 3 printed each on its own line.