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):

containerLay         


        

Answer 1

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
}

Answer 2

Another solution is to implement and use self-reference:

class SelfReference<T>(val initializer: SelfReference<T>.() -> T) {
    val self: T by lazy {
        inner ?: throw IllegalStateException()
    }

    private val inner = initializer()
}

fun <T> selfReference(initializer: SelfReference<T>.() -> T): T {
    return SelfReference(initializer).self
}

Then the usage would be

containerLayout.viewTreeObserver.addOnGlobalLayoutListener(selfReference { 
    OnGlobalLayoutListener {
        containerLayout.viewTreeObserver.removeOnGlobalLayoutListener(self)
        // ...
    }
}

Instead of this, self property is used.

Answer 3

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
    }
})