How I can use callback in Kotlin?

Question

I have View and one CircleShape , which should show toast in this View. And I use it in main Activity. This is my interface

interface OnClickListenerInterfa         


        

Answer 1

On CircleShape.kt.

private listener OnClickListenerInterface? = null
...
fun setOnClickListener(listener: OnClickListenerInterface){
    this.listener = listener
}

On your Activity

mCircleShape.setOnClickListener(object: CircleShape.OnClickListenerInterface {
    override fun onClick(){ // Do something here
    }
}

If you're gonna use lambda expression, you can use a Function Type. Here how it looks like on CirclesShapt.kt

fun setOnClickListener(listener: () -> Unit){
   listener() // or you could use optional if the lister is nullable "listener?.invoke()"
}

So in activity looks like.

mCircleShape.setOnClickListener {
  // Do something here
}