Hello everyone, almost all of us have seen code like or in Kotlin, and when you click on it to see the source code it will show you the Java OnClickListener interface. But have you asked yourself what is this syntax? Is it a Kotlin extension? and how can you call your custom listener like this? In this small article, you will know the answer to all of those questions, so let's start 😋. view.setOnClickListener { } view.setOnLongClickListener { } This syntax is not an extension but SAM conversion, but what does SAM stand for? SAM stands for Single Abstract Method interface and it’s called also Functional interface which is an interface with only one non-default method and any number of default methods, for examples In the JDK we have Runnable class which has only one method called run and in Android SDK we have OnClickListener, OnLongClickListener …etc. How Can We Create a Custom Functional Interface? To declare a Functional interface in Java is easy. You just create a normal interface with one method for example. public interface FunInterface {
    void method();
} And in Kotlin starting from Version 1.4 you need to declare it as a fun interface not only interface for example. fun interface FunInterface {
    fun method()
} In Kotlin you can use Java or Kotlin Functional interfaces as a Lambda expression for example. fun learnFunInterface(fi : FunInterface) { ... } To you this function you can pass FunInterface as an anonymous object for example. learnFunInterface(object : FunInterface { 
    override fun method() {
        println("Hello") 
    } 
}) But because it Functional Interface you can pass it as lambda { } and this is what is called SAM conversion. learnFunInterface ({ println("Hello") }) also in Kotlin if your last parameter is a functional interface you can move your lambda out the brackets ( ) for example. learnFunInterface {
    println("Hello")
} Now you can see that is just because this method takes functional interface which is the as a parameter. setOnClickListener { } OnClickListener Note that the same syntax will work on Kotlin also if your functional interface is written in Java like . OnClickListener Extra Resources: https://kotlinlang.org/docs/fun-interfaces.html https://kotlinlang.org/docs/java-interop.html#sam-conversions https://jorgecastillo.dev/kotlin-sam-conversions You can find me on: , , . GitHub LinkedIn Twitter Enjoy Programming 😋. This article was first published . here

Twitter

The Easy Way to Create Adapters for Your Next Android Project

Regex Refresher: Named Groups and Backreferences

Read My Stories

Hire Me

Portfolio

Nominated for 2022 - Android Advocate of the Year

Nominated for 2022 - HackerNoon Contributor of the Year - Kotlin

Too Long; Didn't Read

Make resilience your competitive advantage

The Interconnection of Functional Interfaces in Java and Kotlin

The Interconnection of Functional Interfaces in Java and Kotlin

About Author

Comments

TOPICS

THIS ARTICLE WAS FEATURED IN

Related Stories

Untitled Story

A Beginners Guide to Creating a Dialogue with Lottie Animation in Android

104 Stories To Learn About Go

105 Stories To Learn About Functional Programming

100+ Free Pluralsight Courses to learn Python, Java, and Spring Boot

10 Websites to Learn JavaScript for Beginners

A Beginners Guide to Creating a Dialogue with Lottie Animation in Android

104 Stories To Learn About Go

105 Stories To Learn About Functional Programming

100+ Free Pluralsight Courses to learn Python, Java, and Spring Boot

10 Websites to Learn JavaScript for Beginners

Light-Mode

Classic

Newspaper

Dark-Mode

Neon Noir

Minty

HN StartUps