A sample of DiffUtil written in Kotlin.

1. Subscribe to state changes. (MainActivity.onStart)
2. When notified state changes, set new state to adapter. (MainActivity.onStart)
3. Transform new state to item list and set to items. (MainAdapter.state)
4. Calculate item list differences and dispatch updates to adapter. (MainAdapter.items)

Diffable is an interface for simplify use DiffUtil.Callback.

Diffable.isTheSame returns true if this and other has same id. Default implementation returns equals. data class should override this.

like this:

override fun isTheSame(other: Diffable) = (id == (other as? Repo)?.id)

Diffable.isContentsTheSame returns true if this equals to other. Default implementation returns equals.