BooleanPreference.kt

class BooleanPreference(
        private val name: String,
        private val default: Boolean = false
) {

    operator fun getValue(thisRef: LocalStorage, property: KProperty<*>): Boolean =
            thisRef.prefs.getBoolean(name, default)

    operator fun setValue(thisRef: LocalStorage, property: KProperty<*>, value: Boolean) =
            thisRef.prefs.edit().putBoolean(name, value).apply()
}

MutableLiveDataProperty.kt

class MutableLiveDataProperty<T>(
        val p: KMutableProperty0<T>
) : MutableLiveData<T>() {
    init {
        postValue(p.get())
        observeForever {
            p.set(it)
        }
    }
}

MutablePropertyDelegate.kt

class MutablePropertyDelegate<T>(
        val p: KMutableProperty0<T>
) {
    operator fun getValue(thisRef: Any, property: KProperty<*>): T = p.get()

    operator fun setValue(thisRef: Any, property: KProperty<*>, value: T) = p.set(value)
}

Sample.kt

// Sample
class LocalStorage(ctx: Context) {
  var showUsername by BooleanPreference("showUsername", true)
}

class DashboardModel(
  private val s: LocalStorage
) {
  var showUsername: Boolean by MutablePropertyDelegate(s::showUsername)
}

class DashboardViewModel(
  private val m: DashboardModel
) {
  val showUsername = MutableLiveDataProperty(m::showUsername)
  
  fun toggleShowUsername() {
    showUsername.postValue(!showUsername.value!!)
  }
}

/*
<TextView text='@{vm.showUsername vm.username ? "..."}' onClick="@{() -> vm.toggleShowUsername()}"
*/