How do you display a Toast using Kotlin on Android?

Issue

In different Kotlin examples for Android I see toast("Some message...") or toastLong("Some long message"). For example:

view.setOnClickListener { toast("Click") }

As I understand, it is an Extension Function for Activity.

How and where do you define this toast() function so that you are able to use it throughout the project?

Solution

It can be an extension function for Context:

fun Context.toast(message: CharSequence) = 
    Toast.makeText(this, message, Toast.LENGTH_SHORT).show()

You can place this anywhere in your project, where exactly is up to you. For example, you can define a file mypackage.util.ContextExtensions.kt and put it there as a top level function.

Whenever you have access to a Context instance, you can import this function and use it:

import mypackage.util.ContextExtensions.toast

fun myFun(context: Context) {
    context.toast("Hello world!")
}

Answered By - nhaarman