Databinding with DelegatedProperties

AccountViewModel.kt

class AccountViewModel : ObservableModel by ObservableModelDelegate() {
  @get:Bindable var name by property<CharSequence>("", BR.name)
  @get:Bindable var authenticated by property(false, BR.authenticated)
  @get:Bindable var avatar by property("", BR.avatar)
}

ObservableModel.kt

import android.databinding.Observable
import android.databinding.PropertyChangeRegistry

fun ObservableModel.notifyPropertyChanged(fieldId: Int) = notifyPropertyChanged(this, fieldId)
fun ObservableModel.notifyChange() = notifyChange(this)

interface ObservableModel : Observable {
  fun notifyPropertyChanged(container: Observable, fieldId: Int)
  fun notifyChange(container: Observable)
}

class ObservableModelDelegate : ObservableModel {
  @Transient private var callbacks: PropertyChangeRegistry? = null

  @Synchronized override fun addOnPropertyChangedCallback(callback: Observable.OnPropertyChangedCallback) {
    if (callbacks == null) {
      callbacks = PropertyChangeRegistry()
    }
    callbacks!!.add(callback)
  }

  @Synchronized override fun removeOnPropertyChangedCallback(callback: Observable.OnPropertyChangedCallback) {
    callbacks?.remove(callback)
  }

  @Synchronized override fun notifyChange(container: Observable) {
    callbacks?.notifyCallbacks(container, 0, null)
  }

  @Synchronized override fun notifyPropertyChanged(container: Observable, fieldId: Int) {
    callbacks?.notifyCallbacks(container, fieldId, null)
  }
}

ObservableModelProperties.kt

import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KProperty

fun <T> ObservableModel.property(initial: T, fieldId: Int, vararg additionalFieldIds: Int): ReadWriteProperty<Any, T> {
  return ObservableModelProperty(initial, this, fieldId, additionalFieldIds)
}

internal abstract class BaseObservableModelProperty<T>(
    private val observableModel: ObservableModel,
    private val fieldId: Int,
    private val additionalFieldIds: IntArray
) : ReadWriteProperty<Any, T> {
  protected abstract var current: T

  override fun getValue(thisRef: Any, property: KProperty<*>): T {
    return current
  }

  override fun setValue(thisRef: Any, property: KProperty<*>, value: T) {
    if (current != value) {
      current = value
      observableModel.notifyPropertyChanged(fieldId)
      additionalFieldIds.forEach {
        observableModel.notifyPropertyChanged(it)
      }
    }
  }
}

internal class ObservableModelProperty<T>(
    initial: T,
    observableModel: ObservableModel,
    fieldId: Int,
    additionalFieldIds: IntArray
) : BaseObservableModelProperty<T>(observableModel, fieldId, additionalFieldIds) {
  override var current = initial
}