GalleryActivity.kt

private fun addUploadRecordToDb(uri: String){
    val db = FirebaseFirestore.getInstance()

    val data = HashMap<String, Any>()
    data["imageUrl"] = uri

    db.collection("posts")
        .add(data)
        .addOnSuccessListener { documentReference ->
            Toast.makeText(this, "Saved to DB", Toast.LENGTH_LONG).show()
        }
        .addOnFailureListener { e ->
            Toast.makeText(this, "Error saving to DB", Toast.LENGTH_LONG).show()
        }
}