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 OnClickListenerInterface {   fun onClick() } 

It is CircleShape( it is View in my xml) and listener in my View. I want to implement OnClick in my Activity.

 var listener: OnClickListenerInterface? = null   mCircleShape.setOnClickListener(View.OnClickListener {       if (listener == null) return@OnClickListener       listener!!.onClick()     }) 

I know , that in Kotlin getters and setters generic automatics, but how I can set listener if it private. It is code from my Activity, but It doesn't work

CircleShape.listener  = object :OnClickListenerInterface{       override fun onClick() {         ToastUtils.showSuccessMessage(getContext(),"pressed")       }     } 

How I should to use Callback, onClickListenere in Kotlin?

Answer 1

A more simpler solution by using lambda.

Inside CircleShape.kt, declare a lambda function.

var listener: (()->Unit)? = null ... // When you want to invoke the listener listener?.invoke() 

Inside your Activity

mCircleShape.listener = {     // Do something when you observed a call } 

Answer 2

define a function like this:

  fun performWork(param1: String, myCallback: (result: String?) -> Unit) {     // perform some network work      // on network finished     myCallback.invoke("result from network")   } 

use like this:

  performWork("http://..."){ result ->   //use result   }