How to reference a lambda from inside it?

Question

I am trying to get height of a view in onCreate method but I couldn't find any way to remove OnGlobalLayoutListener.

In Java (working):

containerLayout.getViewTreeObserver.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {       @Override       public void onGlobalLayout() {           containerLayout.getViewTreeObserver().removeGlobalOnLayoutListener(this);          int width  = layout.getMeasuredWidth();         int height = layout.getMeasuredHeight();       }   }); 

In Kotlin (not accepting "this"):

   containerLayout.viewTreeObserver.addOnGlobalLayoutListener {             containerLayout.viewTreeObserver.removeOnGlobalLayoutListener(this)             Toast.makeText(applicationContext, "size is "+ containerLayout.height,Toast.LENGTH_LONG).show()         } 

Is there any reference or example for this problem? Thanks.

Answer 1

Referencing a lambda from inside it is not supported.

As a workaround, you might use anonymous object instead of lambda SAM-converted to Java functional interface OnGlobalLayoutListener:

containerLayout.viewTreeObserver.addOnGlobalLayoutListener(object: OnGlobalLayoutListener {     override fun onGlobalLayout() {         // your code here. `this` should work     } }) 

Answer 2

What's about extension like this?

import android.annotation.SuppressLint import android.os.Build import android.view.View import android.view.ViewTreeObserver  inline fun View.doOnGlobalLayout(crossinline action: (view: View) -> Unit) {     val vto = viewTreeObserver     vto.addOnGlobalLayoutListener(object : ViewTreeObserver.OnGlobalLayoutListener {         @SuppressLint("ObsoleteSdkInt")         @Suppress("DEPRECATION")         override fun onGlobalLayout() {             action(this@doOnGlobalLayout)             when {                 vto.isAlive -> {                     if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {                         vto.removeOnGlobalLayoutListener(this)                     } else {                         vto.removeGlobalOnLayoutListener(this)                     }                 }                 else -> {                     if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {                         viewTreeObserver.removeOnGlobalLayoutListener(this)                     } else {                         viewTreeObserver.removeGlobalOnLayoutListener(this)                     }                 }             }         }     }) } 

Finally, you can call OnGlobalLayoutListener from View directly

val view: View = ... view.doOnGlobalLayout {   val width = view?.measuredWidth   val height = view?.measuredHeight }