In this article, you will learn how to change Firebase Realtime Database/Cloud Firestore queries without changing the whole adapter of a RecyclerView in Android by using the FirebaseUI-Android library.

Let’s say you need to populate a list using RecyclerView to show data loaded from Firebase Realtime Database or Cloud Firestore and you have implemented a custom RecyclerView.Adapter to hold data or you used FirebaseUI-Android which is an official open-source library developed by the Firebase team. In this article, we’re going to use the FirebaseUI-Android library.

We’ll load data from Firebase Realtime Database/Cloud Firestore and populate a RecyclerView (Simple + Paginated) using the adapter. After that, we’ll change/filter the query based on some user interaction at runtime without changing whole adapter.

In the end, you will see app like this 👇. After clicking on one of the buttons, data in RecyclerView will be replaced by new data.

Demo output after changing the query.

🔥 About FirebaseUI 😃

• FirebaseUI is an open-source library for Android that allows you to quickly connect common UI elements to Firebase APIs. (see here)

• It makes it easy to bind data from Firebase Realtime Database or Cloud Firestore to your app’s UI 🎨.

FirebaseUI-Android provides a number of adapters, such as:

• FirebaseRecyclerAdapter — or binding Firebase Realtime Database

• FirebaseRecyclerPagingAdapter — for binding Firebase Realtime Database with pagination support

• FirestoreRecyclerAdapter — for binding Cloud Firestore

• FirestorePagingAdapter — for binding Cloud Firestore with pagination support

⚡️ Getting Started

Let’s write some code!

Open Android Studio and create a new project. Alternatively, you can simply clone this repository. This is a very simple app for showing a list of posts.

Gradle Setup

In the app module of build.gradle, include following dependencies.

dependencies {
    // Firebase SDKs
    implementation 'com.google.firebase:firebase-firestore:21.4.1'
    implementation 'com.google.firebase:firebase-database:19.2.1'

    // FirebaseUI for Real-time database
    implementation 'com.firebaseui:firebase-ui-database:6.2.0'

    // FirebaseUI for Cloud Firestore
    implementation 'com.firebaseui:firebase-ui-firestore:6.2.0'

    // Paging Library (For Pagination Only)
    implementation 'android.arch.paging:runtime:1.0.1'
}

If you’re unsure how to use FirebaseUI 🔥, check out the official source here. Or, take a look at the official sample👇.

⚡️How to Change the Query 🤔

In the adapter classes of FirebaseUI library, there’s a method updateOptions() which initialises an adapter with new options. Whenever this is invoked, the respective RecyclerView is populated with new data.

💻 Let’s Change the Queries 🔥

#1 — Firebase Realtime Database

Here mAdapter is an instance of FirebaseReyclerAdapter. The new instance of FirebaseRecyclerOptions is created with a query: newQuery. Finally, we call updateOptions() . After this, you can observe the change in RecyclerView. 😃

    fun changeQuery() {
        val newQuery = mBaseQuery
            .orderByChild("timestamp")
            .limitToLast(100)

        // Make new options
        val newOptions = FirebaseRecyclerOptions.Builder<Post>()
            .setQuery(newQuery, Post::class.java)
            .build()

        // Change options of adapter.
        mAdapter.updateOptions(newOptions)
    }

The same can be done in a paging adapter i.e. FirebaseRecyclerPagingAdapter. Just a small change is there while making options is we have to pass PagedList.Config as a parameter along with query in setQuery() .

#2 — Firebase Cloud Firestore

Same as above, here mAdapter is an instance of FirestoreReyclerAdapter.

    fun changeQuery() {
        val newQuery = mCollectionReference
            .orderBy("timestamp")
            .whereEqualTo("seen", false)
            .limitToLast(100)

        // Make new options
        val newOptions = FirestoreRecyclerOptions.Builder<Post>()
            .setQuery(newQuery, Post::class.java)
            .build()

        // Change options of adapter.
        mAdapter.updateOptions(newOptions)
    }

Again, the same can be done in a paging adapter i.e. FirestorePagingAdapter.

We have successfully changed queries at runtime using the FirebaseUI library😃.

The source code for this article is available in this GitHub repo.

Thank You! 😃

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