Kotlin flows are a feature of Coroutines. It serves as a reactive programming framework. Flows were designed to handle an asynchronous stream of data. It is similar to Sequences in Kotlin and also has the benefit of reactive programming. So, in this tutorial, you will learn about Kotlin Flows.

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What Is Kotlin Flows?

You can define a flow in Kotlin as a coroutine that has multiple asynchronously computed values. It is a stream of data that can be computed asynchronously and is used to send multiple values in sequence. 

The data emitted must be of the same type and is also emitted in a sequential manner. A flow uses suspended functions to consume and produce in an asynchronous manner.

Now, go ahead and understand why you need Kotlin Flows.

Why Do You Need Kotlin Flows?

To make an application responsive and boost its performance, asynchronous programming plays a very important role. To make applications, asynchronous RxJava can be used, which is a Java-based extension of ReactiveX.  

In Kotlin, the same functionality is given in the form of Kotlin Flow API. Not only does it have all the operators and functionalities required, but it also supports suspending functions, which helps to perform asynchronous tasks in a sequential manner.

Now, understand how Kotlin flows work.

How Does Kotlin Flow Work?

When data is requested from the server, and asynchronous programming is used to handle that data, then the Flow manages that data in the background thread asynchronously because there might be a chance that some process might run longer to fetch data. Once the data is received and collected in the collector, then it is displayed using the recycler view.

Kotlin_Flows_1

A Flow is a sequence of values that uses suspend functions to produce and consume values asynchronously.  

A flow consists of three entities:

  • Producer

  • Intermediary

  • Consumer

Kotlin_Flows_2.

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Producer: A producer is used to emit the data, which is added to the stream.

Intermediary: It can modify the value which is emitted into the stream.

Consumer: A consumer receives the value from the stream.

Now that you have understood How Kotlin Flows work, let’s go ahead and create a Kotlin Flow.

Creating a Kotlin Flow

To create a Flow, first, you need to create a producer.

Producer

A producer is the one that is used to emit the data. So to create one, open the Main.kt, and instead of the main, write suspend fun (name of the function) main. It is named suspended because it will call other suspending functions, and only a suspending function can do that.

/Kotlin_Flows_3.

After that, you will create a flow builder to create a flow producer. The flow will emit integer values one by one from 0 to 9 and a delay of 2000 milliseconds or 2 seconds to create a long-running task.

The emit() will help in sending values to the consumer.

Before moving on to the Consumer, you will understand the cold stream and hot stream.

The Cold stream doesn’t produce any value until or unless the Consumer is there to collect them, whereas the Hot stream produces the values even if there is no consumer.

Now Flow is an example of a cold stream, so we will create a Consumer to collect the values.

Consumer

In Consumer, first, you will launch a coroutine because we have to use a flow builder function, which is the collect function that needs to be kept inside the coroutine. The collect is used to collect the values emitted by it.

Kotlin_Flows_4.

Here, the delay is used because there can be a condition of backpressure. The backpressure occurs when the Consumer is not done consuming the data, and the Producer is producing it, which can result in data loss.

So to avoid such a case, you use delay() inside the collect function. The delay (3000) will add a delay of 3 seconds.

Now, you can run the main function and check for the displayed values. That is how the Flow is created.

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Conclusion

In this tutorial on Kotlin Flows, you understand why you need Kotlin Flows and learned what Kotlin Flows are. You also explored how Kotlin flows work and understood how to create a Kotlin flow. You also learned about the Producer, Consumer, and backpressure.

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Do you have any questions regarding this tutorial on Kotlin Flows? If you do, then put them in the comments section. We’ll help you solve your queries. 

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