Android Load FirestoreUI FirestoreRecyclerAdapter With Empty Query (Clear RecyclerView)

April 8, 2019

EmptySnapshotArray

I am using FirestoreRecyclerAdapter to load firestore query into RecyclerView.

Why need empty query/empty recycler view?

I already loaded RecyclerView with Query data when user signin, then I need to empty/clear the RecyclerView when user signout.

I could hide the RecyclerView
Or create a Firestore Query which I am sure will not return any result.
Or I can create a blank RecyclerView.Adapter where getItemCount() return 0.
Or I can use FirestoreRecyclerOptions.Builder#setSnapshotArray (instead of setQuery) and assign an empty snapshot array.

EmptySnapshotArray

import com.firebase.ui.firestore.ObservableSnapshotArray
import com.firebase.ui.firestore.SnapshotParser
import com.google.firebase.firestore.DocumentSnapshot

class EmptySnapshotArray<T>: ObservableSnapshotArray<T>(SnapshotParser<T> {
    TODO()
}) {
    // class EmptyArray<T>(parser: SnapshotParser<T>): ObservableSnapshotArray<T>(parser) {
    override fun getSnapshots(): MutableList<DocumentSnapshot> {
        return mutableListOf()
    }
}

class MyActivity:  AppCompatActivity() {

    private lateinit var adapter: LocalAdapter

    private fun createAdapter(): LocalAdapter {
        if (::adapter.isInitialized) {
            // call this before replacing the adapter to prevent invalid snapshot
            adapter.stopListening()
            lifecycle.removeObserver(adapter)
        }

        // query=null when user not signin
        val query = ...

        // Quote is Model
        val builder = FirestoreRecyclerOptions.Builder<Quote>()
            .setLifecycleOwner(this)

        if (query != null) {
            builder.setQuery(query, object : SnapshotParser<Quote> {
                override fun parseSnapshot(snapshot: DocumentSnapshot): Quote {
                    return Quote.toObject(snapshot)!!.also {
                        it.id = snapshot.id
                    }
                }
            })
        }
        else {
            // no query, set empty
            builder.setSnapshotArray(EmptySnapshotArray())
        }

        val options = builder.build()
        return FirestoreQuoteAdapter(options, viewModel).also {
            adapter = it
        }
    }

    private fun initUi() {
        recyclerView.adapter = createAdapter()
    }
}