[messages] dynamic messages list loading

Author: capcom6

app/src/main/java/me/capcom/smsgateway/data/dao/MessagesDao.kt

@@ -38,8 +38,8 @@ interface MessagesDao {
     )
     fun getMessagesStats(): LiveData<MessagesTotals>
 
-    @Query("SELECT * FROM message ORDER BY createdAt DESC LIMIT 50")
-    fun selectLast(): LiveData<List<Message>>
+    @Query("SELECT * FROM message ORDER BY createdAt DESC LIMIT :limit")
+    fun selectLast(limit: Int): LiveData<List<Message>>
 
     /**
      * FIFO: oldest pending first (priority DESC, createdAt ASC)

app/src/main/java/me/capcom/smsgateway/modules/messages/MessagesRepository.kt

@@ -19,7 +19,7 @@ import java.util.Date
 class MessagesRepository(private val dao: MessagesDao) {
     private val gson = GsonBuilder().serializeNulls().create()
 
-    val lastMessages = dao.selectLast().distinctUntilChanged()
+    fun selectLast(limit: Int) = dao.selectLast(limit).distinctUntilChanged()
 
     val messagesTotals: LiveData<MessagesTotals> = dao.getMessagesStats().distinctUntilChanged()
 

app/src/main/java/me/capcom/smsgateway/modules/messages/vm/MessagesListViewModel.kt

@@ -1,17 +1,45 @@
 package me.capcom.smsgateway.modules.messages.vm
 
 import androidx.lifecycle.LiveData
+import androidx.lifecycle.MediatorLiveData
+import androidx.lifecycle.MutableLiveData
 import androidx.lifecycle.ViewModel
+import androidx.lifecycle.switchMap
 import me.capcom.smsgateway.data.entities.Message
 import me.capcom.smsgateway.data.entities.MessagesTotals
 import me.capcom.smsgateway.modules.messages.MessagesRepository
 
 class MessagesListViewModel(
-    messagesRepo: MessagesRepository
+    private val messagesRepo: MessagesRepository
 ) : ViewModel() {
-    val messages: LiveData<List<Message>> =
-        messagesRepo.lastMessages
-
     val totals: LiveData<MessagesTotals> =
         messagesRepo.messagesTotals
+
+    private val _limit = MutableLiveData<Int>(chunkSize)
+    private val _messages = MediatorLiveData<List<Message>>()
+    val messages: LiveData<List<Message>> = _messages
+
+    init {
+        _messages.addSource(_limit.switchMap { messagesRepo.selectLast(it) }) {
+            _messages.value = it
+            hasMore = it.size >= (_limit.value ?: chunkSize)
+            isLoading = false
+        }
+        loadMore()
+    }
+
+    private var isLoading = false
+    private var hasMore = true
+
+    fun loadMore(index: Int = 0) {
+        val currentLimit = _limit.value ?: 0
+        if (currentLimit >= index + chunkSize || isLoading || !hasMore) return
+
+        isLoading = true
+        _limit.value = currentLimit + chunkSize
+    }
+
+    companion object {
+        private const val chunkSize = 50
+    }
 }

app/src/main/java/me/capcom/smsgateway/ui/MessagesListFragment.kt

@@ -7,13 +7,16 @@ import android.view.ViewGroup
 import androidx.fragment.app.Fragment
 import androidx.fragment.app.commit
 import androidx.recyclerview.widget.DividerItemDecoration
+import androidx.recyclerview.widget.LinearLayoutManager
+import androidx.recyclerview.widget.RecyclerView
 import me.capcom.smsgateway.R
 import me.capcom.smsgateway.data.entities.Message
 import me.capcom.smsgateway.databinding.FragmentMessagesListBinding
 import me.capcom.smsgateway.modules.messages.vm.MessagesListViewModel
 import me.capcom.smsgateway.ui.adapters.MessagesAdapter
 import org.koin.androidx.viewmodel.ext.android.viewModel
 
+
 class MessagesListFragment : Fragment(), MessagesAdapter.OnItemClickListener<Message> {
 
     private val viewModel: MessagesListViewModel by viewModel()
@@ -34,6 +37,7 @@ class MessagesListFragment : Fragment(), MessagesAdapter.OnItemClickListener<Mes
         super.onViewCreated(view, savedInstanceState)
 
         binding.recyclerView.adapter = messagesAdapter
+        binding.recyclerView.addOnScrollListener(scrollListener)
         binding.recyclerView.addItemDecoration(
             DividerItemDecoration(requireContext(), DividerItemDecoration.VERTICAL)
         )
@@ -58,20 +62,32 @@ class MessagesListFragment : Fragment(), MessagesAdapter.OnItemClickListener<Mes
         }
     }
 
+    override fun onItemClick(item: Message) {
+        parentFragmentManager.commit {
+            replace(R.id.rootLayout, MessageDetailsFragment.newInstance(item.id))
+            addToBackStack(null)
+        }
+    }
+
     override fun onDestroyView() {
+        binding.recyclerView.removeOnScrollListener(scrollListener)
         super.onDestroyView()
         _binding = null
     }
 
+    private val scrollListener = object : RecyclerView.OnScrollListener() {
+        override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
+            super.onScrolled(recyclerView, dx, dy)
+
+            val linearLayoutManager = recyclerView.layoutManager as? LinearLayoutManager
+            linearLayoutManager?.findLastVisibleItemPosition()?.let {
+                if (it == messagesAdapter.itemCount - 1) viewModel.loadMore(messagesAdapter.itemCount)
+            }
+        }
+    }
+
     companion object {
         fun newInstance() =
             MessagesListFragment()
     }
-
-    override fun onItemClick(item: Message) {
-        parentFragmentManager.commit {
-            replace(R.id.rootLayout, MessageDetailsFragment.newInstance(item.id))
-            addToBackStack(null)
-        }
-    }
 }