How to get the Next and Previous piece of data from the Firestore Database using Kotlin in Android Studio?

Question

I am trying to iterate through the database documents and have the fields update with the click of the next button and previous button. As of right now, it's only happening with one and then it stops. I don't know why it only does it once and stops. Any reason as to why? Here is a snapshot of what I got right now.

This image is hardcoded in there with the code that is below here.

[![private lateinit var locationTextView: TextView
    private lateinit var descriptionTextView: TextView
    private lateinit var previousArrow: Button
    private lateinit var nextArrow: Button
    private lateinit var usersImage: ImageView][2]][2]

val db = FirebaseFirestore.getInstance()
db.collection("Post").orderBy("timestamp")
    val docRef = db.collection("Post").document("Puppy")
    docRef.get()
        .addOnSuccessListener { document ->
            if (document != null) {
                Log.d("Exists", "DocumentSnapshot data: ${document.data}")

               // locationTextView.text = document.getString("locationTitle")
                locationTextView.setText(document.getString("Name"))
                descriptionTextView.setText(document.getString("description"))
                val imageName = "Puppy"
                val storageRef = FirebaseStorage.getInstance().reference.child("Images/$imageName")

                val localFile = File.createTempFile("tempImage", "jpeg")
                storageRef.getFile(localFile).addOnSuccessListener {

                    val bitmap = BitmapFactory.decodeFile(localFile.absolutePath)
                    usersImage.setImageBitmap(bitmap)
                }
            }
            else {
                Log.d("noExist", "No Such Document")
            }
        }

However, I want to be able to implement these two buttons, so I can get rid of the code above and have it just pull from the database and navigate through each Post with the click of the buttons. I added this onto my next button and it is able to iterate only once. Is there a way that I can iterate through the size of the documents, that way I can go through all of them and not just once?

 nextArrow.setOnClickListener {


val first = db.collection("Post").orderBy("timestamp").limit(1)
            first.get()
                .addOnSuccessListener { documentSnapshots ->

                    val lastVisible = documentSnapshots.documents[documentSnapshots.size() - 1]
                    val next = db.collection("Post").orderBy("timestamp").startAfter(lastVisible).limit(2)
                        next.get().addOnSuccessListener { documents ->
                            for (document in documents) {
                                Log.d(TAG, "${document.id} => $${document.data}")
                                locationTextView.setText(document.getString("Name"))
                                descriptionTextView.setText(document.getString("description"))
                            }
                        }
                    val imageName = "Puppy"
                    val storageRef = FirebaseStorage.getInstance().reference.child("Images/$imageName")

                    val localFile = File.createTempFile("tempImage", "jpeg")
                    storageRef.getFile(localFile).addOnSuccessListener {
                        val bitmap = BitmapFactory.decodeFile(localFile.absolutePath)
                        usersImage.setImageBitmap(bitmap)
                    }
                }
    }
    previousArrow.setOnClickListener { 
        
    }

Here is a snapshot of my database.

Again, to clarify, I am trying to iterate through my database with the Posts with the click of those buttons. Also, the images are stored in a firebase storage database since it's too large for firestore.

Sounds like you're looking to paginate the data, which in Firestore works based on so-called cursors as explained here: https://firebase.google.com/docs/firestore/query-data/query-cursors — Frank van Puffelen, Dec 16 '21 at 01:03
@FrankvanPuffelen I've encountered that page numerous of times before asking this question. It provides some information, but not exactly on the task that I am trying to perform with my buttons. — Adan Vivero, Dec 16 '21 at 21:38

score 1 · Accepted Answer · edited Dec 18 '21 at 08:03

1

As also @FrankvanPuffelen mentioned in his comment, what you are looking for is a pagination algorithm. Since all your images are represented by a documents inside the "Post" collection, it means that you can create a query to load a single image and then load all subsequent images one at a time.

I have answered a similar question a few years ago, where the OP wanted to load more results on a button click:

Is there a way to paginate queries by combining query cursors using FirestoreRecyclerAdapter?

In your case, the first query would be:

val db = FirebaseFirestore.getInstance()
val firstQuery = db.collection("Post").orderBy("timestamp").limit(1)

To construct the second query, inside the first callback you have to get the last visible item using:

val lastVisible = queryDocumentSnapshots.documents[queryDocumentSnapshots.size() - indexFam]

And perform the query:

val next = db.collection("Post").orderBy("timestamp").startAfter(lastVisible).limit(1)

inside this function:

private fun getNext(first: Query, db: FirebaseFirestore, indexFam: Int) {
        first.get().addOnSuccessListener { queryDocumentSnapshots ->
            val lastVisible = queryDocumentSnapshots.documents[queryDocumentSnapshots.size() - indexFam]
            val next = db.collection("Post").orderBy("timestamp").startAfter(lastVisible).limit(1)
            next.get().addOnSuccessListener { documents ->
                for (document in documents) {
                    Log.d(TAG, "${document.id} => $${document.data}")
                    // Whatever you want to iterate right here. 
                }
            }
        }
    }

edited Dec 18 '21 at 08:03

Adan Vivero

422
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answered Dec 16 '21 at 08:25

Alex Mamo

130,605
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What is "task" declared to be? Is lastVisible going inside the addOnSuccessListener? – Adan Vivero Dec 16 '21 at 20:30
The "task" is the argument from onComplete. Please check the [linked answer](https://stackoverflow.com/questions/50592325/is-there-a-way-to-paginate-queries-by-combining-query-cursors-using-firestorerec/50692959). Give it a try and tell me if it works. – Alex Mamo Dec 16 '21 at 21:04
That's in Java... – Adan Vivero Dec 16 '21 at 21:05
You can simply convert Java code into Kotlin code. – Alex Mamo Dec 16 '21 at 21:09
Is there a tool in Android Studio to do that? I'm still fairly new to Kotlin and I'm still learning. It's not as easy to just look at Java code and fluently write it in Kotlin. – Adan Vivero Dec 16 '21 at 21:09
Right now it's only iterating once. I don't know why it doesn't keep going? – Adan Vivero Dec 16 '21 at 23:42
Have you tried to use something like this `lastVisible = task.result.documents.get(task.result.size() - 1)`? – Alex Mamo Dec 17 '21 at 07:41
Yes, with some errors though. How is the onComplete suppose to be implemented? Are we talking about an addOnCompleteListener? I'm getting an error with that. – Adan Vivero Dec 17 '21 at 21:10
I switched it to val lastVisible = task.result?.documents?.get((task.result?.size() ?: -1)) as it cleaned up my errors, but not really doing what I want it to do. – Adan Vivero Dec 17 '21 at 21:18
I think I found my solution. – Adan Vivero Dec 17 '21 at 23:11
1

I found my solution. I just had to keep updating the number of lastvisible to keep going down. – Adan Vivero Dec 18 '21 at 01:52
Good to hear that, Adan. – Alex Mamo Dec 18 '21 at 08:03

score 0 · Answer 2 · answered Dec 23 '21 at 21:56

Here is how I solved this using my method onto my onCreate():

private lateinit var locationTextView: TextView
private lateinit var descriptionTextView: TextView
private lateinit var previousArrow: Button
private lateinit var nextArrow: Button
private lateinit var usersImage: ImageView

val db = FirebaseFirestore.getInstance()
val first = db.collection("Post").orderBy("timestamp")
getNext(first, db, 2) // This is the original pop up

getPostSizeAsync(first) { postSize ->
  nextArrow.setOnClickListener {
           nextClicker++
      if(nextClicker == postSize) {
           nextClicker = 2
      }
      getNext(first, db, nextClicker)
      }
}


// This is for the previous button clicker
previousArrow.setOnClickListener {
        if(nextClicker > 1)
        {
            nextClicker--
            getNext(first, db, nextClicker)
        }
}

And then with the private functions:

 private fun getNext(first: Query, db: FirebaseFirestore, indexFam: Int) {
        first.get().addOnSuccessListener { queryDocumentSnapshots ->
            val lastVisible = queryDocumentSnapshots.documents[queryDocumentSnapshots.size() - indexFam]
            val next = db.collection("Post").orderBy("timestamp").startAfter(lastVisible).limit(1)
            next.get().addOnSuccessListener { documents ->
                for (document in documents) {
                    Log.d(TAG, "${document.id} => $${document.data}")
                    locationTextView.setText(document.getString("Name"))
                    descriptionTextView.setText(document.getString("description"))
                    val imageName = document.getString("Name")
                    val storageRef = FirebaseStorage.getInstance().reference.child("Images/$imageName")
                    val localFile = File.createTempFile("tempImage", "jpeg")
                    storageRef.getFile(localFile).addOnSuccessListener {
                        val bitmap = BitmapFactory.decodeFile(localFile.absolutePath)
                        usersImage.setImageBitmap(bitmap)
                    }
                }
            }
        }
    }
private fun getPostSizeAsync(first: Query, callback: (Int) -> Unit) {
        first.get().addOnSuccessListener { documents ->
            val postSize = documents.count()
            callback(postSize)
        }
    }

How to get the Next and Previous piece of data from the Firestore Database using Kotlin in Android Studio?

2 Answers2