FragmentViewBinder.kt

import android.view.View
import androidx.fragment.app.Fragment
import androidx.lifecycle.Lifecycle
import androidx.lifecycle.LifecycleObserver
import androidx.lifecycle.OnLifecycleEvent
import java.lang.ref.WeakReference
import kotlin.properties.ReadOnlyProperty
import kotlin.reflect.KProperty

public fun <V : View> Fragment.bindView(id: Int): ReadOnlyProperty<Fragment, V> = ViewFinderProperty(id)

private class ViewFinderProperty<V : View>(val viewId: Int) : ReadOnlyProperty<Fragment, V> {

  private var viewRef: V? = null
  private var lifecycleObserver: LifecycleObserver? = null

  override fun getValue(thisRef: Fragment, property: KProperty<*>): V {
    return viewRef?.let { it } ?: findView(thisRef, viewId)
  }

  private fun findView(fragment: Fragment, id: Int): V {
    attachLifecycleObserver(fragment)
    return fragment.view!!.findViewById(id)
  }

  private fun attachLifecycleObserver(fragment: Fragment) {
    if (lifecycleObserver == null) {
      createLifecycleObserver().also { safeObserver ->
        lifecycleObserver = safeObserver
        fragment.lifecycle.addObserver(safeObserver)
      }
    }
  }

  private fun createLifecycleObserver() = object : LifecycleObserver {
    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
    fun onDestroyView() {
      viewRef = null
    }
  }
}