BindViewPropertyDelegate.kt

class BindView<V: View>(@IdRes val id: Int): ReadOnlyProperty<Any, V> {

  private var view: V? = null

  override fun getValue(thisRef: Any, property: KProperty<*>): V {
    return view ?: getViewInitial(thisRef)
  }

  private fun getViewInitial(thisRef: Any): V {
    val foundView: V = when (thisRef) {
      is AppCompatActivity -> thisRef.findViewById(id) ?: throw Exception("view not found")
      is Fragment -> {
        val fragmentView = thisRef.view ?: throw Exception("fragment view is currently null.")
        fragmentView.findViewById(id) ?: throw Exception("view not found")
      }
      is ViewGroup -> thisRef.findViewById(id) ?: throw Exception("view not found")
      is RecyclerView.ViewHolder -> thisRef.itemView.findViewById(id) ?: throw Exception("view not found")
      else -> throw Exception("bind view property delegate used in unsupported class ${thisRef.javaClass.simpleName}")
    }
    view = foundView
    return foundView
  }

}

class BindNullableView<V: View>(@IdRes val id: Int): ReadOnlyProperty<Any, V?> {

  private var view: V? = null
  private var checkedForView = false

  override fun getValue(thisRef: Any, property: KProperty<*>): V? {
    return when (checkedForView) {
      true -> view
      else -> getViewInitial(thisRef)
    }
  }

  private fun getViewInitial(thisRef: Any): V? {
    val foundView: V = when (thisRef) {
      is AppCompatActivity -> thisRef.findViewById(id)
      is Fragment -> {
        val fragmentView = thisRef.view ?: throw Exception("fragment view is currently null.")
        fragmentView.findViewById(id)
      }
      is ViewGroup -> thisRef.findViewById(id)
      is RecyclerView.ViewHolder -> thisRef.itemView.findViewById(id)
      else -> throw Exception("bind view property delegate used in unsupported class ${thisRef.javaClass.simpleName}")
    }
    view = foundView
    checkedForView = true
    return foundView
  }

}

//Examples in use

class SomeFragment: Fragment() {

  val someButton by BindView<Button>(R.id.nextButton)
  val someTextView by BindNullableView<TextView>(R.id.text_accepted_offer_from)


}

class SomeViewHolder(itemView): RecyclerView.ViewHolder(itemView) {
  
  val someCoolView by BindView<View>(R.id.view_empty)
  val someOtherViewWhichMightBeNull by BindNullableView<LinearLayout>(R.id.vehicle_headline)
  
}