Kotlin Flow: A Comprehensive Guide

Halil Özel
2 min readJun 9, 2024

Kotlin Flow is a powerful asynchronous programming library introduced in Kotlin 1.3. It is built on top of Kotlin coroutines and provides a reactive way to handle streams of data. Flow simplifies asynchronous programming by making it easier to write code that is declarative, composable, and resilient.

Kotlin Flow

What is Flow? ⛓️

A Flow is a stream of data that emits values over time. It is similar to a reactive stream, but it is specifically designed to work with Kotlin coroutines. This means that you can use Flow to write asynchronous code that is non-blocking and easy to understand.

Benefits of Using Flow 🔋

There are many benefits to using Flow, including:

  • Declarative: Flow code is declarative, which means that you can describe what you want to happen without having to worry about how it is implemented. This makes Flow code easier to read and write.
  • Composable: Flow operators can be composed together to create complex data streams. This makes Flow a powerful tool for data processing.
  • Resilient: Flow can handle errors and backpressure gracefully. This makes Flow code more reliable and easier to maintain.

Getting Started with Flow 🎛️

To get started with Flow, you first need to add the Kotlin coroutines and Flow libraries to your project. You can do this by adding the following dependencies to your build.gradle file:

dependencies {
implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:1.8.1"
implementation "org.jetbrains.kotlinx:kotlinx-coroutines-flow:1.8.1"
}

Once you have added the dependencies, you can start using Flow by creating a flow. You can create a flow using the flowfunction or by using a builder function.

Here is an example of how to create a flow using the flow function:

val numbersFlow = flow {
emit(1)
emit(2)
emit(3)
}

Flow Operators 💡

Flow operators are functions that can be used to transform and manipulate flows. There are a wide variety of flow operators available, including:

  • map: Maps each value in the flow to a new value.
  • filter: Filters the values in the flow based on a predicate.
  • combine: Combines two or more flows into a single flow.
  • buffer: Buffers the values in the flow.
  • collect: Collects the values in the flow into a collection.

Using Flow with Coroutines 🔌

Flow can be used with coroutines to write asynchronous code. You can use the collect operator to collect the values in a flow and then process them in a coroutine.

Here is an example of how to collect the values in a flow and print them to the console:

numbersFlow.collect { value ->
println(value)
}

Conclusion 🎀

Kotlin Flow is a powerful asynchronous programming library that can be used to write declarative, composable, and resilient code. If you are writing asynchronous code in Kotlin, I encourage you to learn more about Flow.

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